It is very convenient to work in any metal processing workshop if you have a welding machine at hand. With its help, you can reliably connect metal parts or structures, cut holes, or even simply cut workpieces in the right place.
You can make such a useful tool with your own hands, the main thing is to understand everything thoroughly, and the skill of making a beautiful and reliable seam will come with experience.
Variable output current
At home, in the country, in production, these are the devices most often found. Many photos of welding equipment show that it was made by hand.
The most important components for such a device are the wire for two windings and the core for them. In fact, it is a transformer for reducing voltage.
Wire sizes
The device will work quite well with an output voltage of 60 volts and a current of up to 160 amperes. Calculations show that for the primary winding you need to take a copper wire with a cross-section of 3, or better yet, 7 square millimeters. For aluminum wire, the cross-section should be 1.6 times larger.
It is necessary to use fabric insulation for the wires because the wires get very hot during operation and the plastic will simply melt.
The primary winding must be laid very carefully and carefully because it has many turns and is located in a high-voltage area. It is desirable that the wire be without breaks, but if the required length is not at hand, then the pieces must be securely connected and soldered.
Secondary winding
For the secondary winding you can use copper or aluminum. The wire can be either single-core or consisting of several conductors. Section from 10 to 24 square millimeters.
It is very convenient to wind the coil separately from the core, for example, on a wooden blank, and then assemble transformer steel plates into a finished, reliably insulated winding.
Stranded wire
How to make a stranded wire of a suitable cross-section for a welding machine? There is such a way. At a distance of 30 meters (more or less, depending on calculations), two hooks are securely attached. The required amount of thin wire is stretched between them, from which a stranded conductor will be made. Then one end is removed from the hook and inserted into an electric drill.
At low speeds, the bundle of wires is evenly twisted, its total length will decrease slightly. Strip the ends of the wire (each wire separately), tin and solder thoroughly. Then insulate the entire wire, preferably with textile-based insulating material.
Core
Homemade welding machines based on transformer steel cores show good performance. They are made from plates 0.35-0.55 millimeters thick.
It is important to choose the right size of the window in the core so that both coils fit into it, and the sectional area (its thickness) is 35-50 square centimeters. Bolts are installed at the corners of the finished core, and everything is tightened tightly with nuts.
The primary winding consists of 215 turns. To be able to regulate the welding current of the finished machine, conclusions can be drawn from winding at 165 and 190 turns.
All contacts are mounted on a plate of insulating material and labeled. The circuit is as follows: the more turns of the coil, the greater the current at the output. The secondary winding consists of 70 turns.
Inverter
You can assemble another welding device with your own hands - this is an inverter. It has a number of positive differences from the transformer. The very first thing that catches your eye is its light weight. Just a few kilograms. You can work without removing the device from your shoulder. Then, the working constant current allows you to create a more accurate seam, and the arc does not jump around as much. Easier to work for novice welders.
Parts for assembling such a device are sold in stores and on the market. You just need to know the markings. The quality of transistors requires special attention because they are located in the most stressed area of the inverter design circuit. To cool the device use forced ventilation in the form of cooling radiators and exhaust fans.
Thus, if you compile a catalog of homemade welding machines, you will get a long list of transformers of various designs, inverters, semi-automatic welding machines and automatic machines. Such devices allow you to work with cast iron and steel, aluminum and copper, stainless steel and thin sheet iron.
The reliability and durability of their operation depends on the accuracy of calculations, the availability of materials, parts, correct assembly, as well as on compliance with safety rules at all stages of the creation and operation of such devices.
Photo of a welding machine at home
Housework always requires a certain set of tools, devices, and a variety of equipment. This is felt especially acutely by owners of private houses and those engaged in various types repairs in our own workshops and garages. Purchasing expensive equipment is not always justified, since its use will not be constant, but assembling a welding machine with your own hands is within the capabilities of every craftsman.
Before starting the process, it is necessary to determine the power of the device, because its dimensions and capabilities will depend on this. To familiarize yourself with the assembly procedure, you can watch the corresponding video, which shows how you can make a practical welding machine with your own hands. Its manufacture will require some theoretical training, as well as experience in electromechanical work. Electrical equipment is assembled at home using preliminary calculations, taking into account both input and output parameters of the device.
This electric device will be useful not only to welders who perform some work at home or in the garage, but also to ordinary craftsmen who use a welding device to build various devices.
Features of homemade transformers
Self-assembled devices differ from factory-made equipment in their technical design. Do-it-yourself welding is made from available elements and assemblies, for which a welding transformer circuit is used. If the parameters of the component parts are strictly observed, the electric device will serve reliably for many years. Before making a welding transformer device with your own hands, you need to decide on the available components. The basis is a transformer consisting of a magnetic core, as well as primary and secondary windings. You can purchase it separately, adapt an existing one, or make it yourself. To make a welded electrical apparatus with your own hands, transformer iron and wire for windings will be added to the variety of tools from scrap materials. The manufactured transformer must be able to connect to a 220 V household power supply and have an output voltage of about 60-65 V for welding thick metals.
Features of homemade rectifiers
Self-made rectifiers allow you to weld thin sheet metal with high quality seam joints.
The circuit of a welding machine using electric current rectification is very simple. It contains a transformer to which a rectifier unit is connected, as well as a choke. This simplest design ensures stable combustion of the welded electric arc. A coil of copper wires wound around a core is used as a choke. The rectifying device is connected directly to the terminals of the step-down transformer winding.
Depending on your goals, you can build a mini welded electrical apparatus yourself. It will cope perfectly with metals of small thickness that do not require the use of high currents when connecting. A spotter can be made from a welded electrical apparatus, which will significantly expand the possibilities of its use.
How to make a welding machine
A hand-made electric welding device is designed to perform minor works around the house, around the house or in the garage. At the first stage, the necessary calculations are performed and assembly parts and assemblies are prepared. To assemble a welding transformer with your own hands, it is advisable to decide in advance where to assemble the device. This will streamline the manufacturing process. Next to it are assembled assembly units that allow you to assemble a simple electric welding machine with your own hands. In addition to the main voltage converter, you will need a choke, which can be used from the elements of a fluorescent lamp. In the absence of a ready-made element, it is made independently from a magnetic core from a powerful starter and a wire made of copper conductors with a cross-section of about 1 mm square. A self-made electric welding machine will differ from its counterparts not only in appearance, but also in characteristics. To decide how to make it, check out similar devices in the photo or video.
Calculation of a welding transformer
Electric welding homemade devices are made according to the simplest scheme, which does not involve the use of additional components. The power of the assembled electrical apparatus will depend on the required value of the welded electric current. Welding at the dacha electrical device assembled with your own hands will directly depend on technical characteristics own product.
When calculating the power for welding, take the strength of the required welding current and multiply this value by 25. The resulting value, when multiplied by 0.015, will show the required cross-sectional diameter of the magnetic core for welding. Before making calculations for the windings, you will have to remember other mathematical operations. To obtain the cross-section of the higher voltage winding, the power value is divided by two thousand, and then multiplied by 1.13. The calculation method for the primary and secondary windings is different.
To obtain winding values for the lowest voltage transformer, you will have to spend a little more time. The cross-sectional area of the secondary winding depends on the density of the welded electric current. For values of 200 A this will be 6 A/mm sq., with figures of 110-150 A - up to 8, and up to 100 A - 10. When determining the cross-section of the lower winding, the strength of the welded electric current is divided by the density, and then multiplied by 1.13.
The number of turns is calculated by dividing the cross-sectional area of the transformer magnetic circuit by 50. In addition, the final welding result will be influenced by the output voltage. It affects the characteristics of the process and can be increasing in current, flat or steep. This affects the oscillations of the electric arc during operation, in which minimal current changes are important when working at home.
Welding transformer circuit
The figure below shows a diagram of a welding transformer of the simplest type.
You can find electrical circuits that will be supplemented with straightening devices and other elements to improve the welded electrical apparatus. However, the main component is still a conventional transformer. The wiring diagram for connecting its wires is quite simple. The welded device is connected through an electrical switching device and fuses to a 220 V household power supply. The use of electrical protective devices is mandatory, as this will protect the network from overloads during emergency conditions.
a – network winding on both sides of the core;
b – the corresponding secondary (welding) winding, connected in counter-parallel;
c – network winding on one side of the core;
g – the corresponding secondary winding, connected in series.
Defining parameters
To make an electric welding machine, you need to understand the principle of operation. It converts the input voltage (220 V) into a reduced voltage (up to 60-80 V). During this process, the low electric current in the primary winding (about 1.5 A) increases in the secondary (up to 200 A). This direct dependence of the operation of transformers is called the voltage-current characteristic of the step-down type. The operation of the device depends on these indicators. Based on it, calculations are carried out and the design of the future apparatus is determined.
Nominal operating mode
Before welding, it is necessary to determine its future nominal use. It shows how long home-made welding equipment can be continuously cooked and how long it should cool down. This indicator is also called the duration of inclusion. For homemade electrical devices, it is located around 30%. This means that out of 10 minutes he is able to work continuously for 3 minutes and rest for 7 minutes.
Rated operating voltage
The operation of a transformer welding device is based on reducing the input voltage to the operating nominal value. When manufacturing a welding machine, you can make any value of the output parameters (30-80 V), which directly affects the range of operating electric currents. Unlike a 220 V power supply, the output value can be of the order of 1.5-2 Volts in products for spot electric welding. This is due to the need to obtain high level current
Mains voltage and number of phases
The current connection diagram for a home-made welding transformer is designed for connection to a household single-phase electrical network. For powerful welding devices, an industrial network with three phases of 380 V is used. The rest of the calculations are performed from the value of this input parameter. Do-it-yourself mini welding uses connection to the home electrical network and does not require high supply voltages.
Open circuit voltage
A household welder assembled by yourself must have a voltage level sufficient to ignite the electric arc. The higher this value, the easier it will appear. The manufacture of the device must comply with current safety regulations, which limit the output voltage to a maximum of 80 V.
Rated welding current of the transformer
Before you make an electric welding machine yourself, you need to decide on the size of the rated current. The ability to perform the work itself on metals of various thicknesses will depend on it. For household electric welding, a value of 200 A is quite sufficient, which allows you to make a fully functional device. Excess this indicator will require an increase in the power of the electrical transformer, which affects both the increase in its dimensions and weight.
Build process
The manufacture of a homemade electric welding machine begins with performing the necessary calculations. The values of the input and output voltages, as well as the required amount of electric current, are taken into account. The size of the device and the amount of materials required directly depend on this. It is not very difficult to make an electric welding machine, like other equipment, with your own hands. With proper design and use of high-quality components, it can reliably serve for decades. For the base, a wire with copper conductors is used, as well as a core made of magnetically permeable iron. The remaining components are not so essential and can be selected from those that can be easily obtained.
Where to start the preparatory stage
After completing the calculation part, materials are prepared and a workplace is equipped for assembling the structure. To build a homemade welding machine, you will need wires for the primary and secondary windings, for the core - suitable transformer iron, insulating materials (varnished fabric, textolite, glass tape, electrical cardboard). In addition, you should take care in advance about a winding machine for making windings, metal elements for frame and switching electrical apparatus. During the assembly process you will need a set of regular metalworking tools. Choose a more spacious workplace so that you can freely wind the coils and engage in the assembly process.
Assembly of the structure
Having completed the preparatory activities, they proceed directly to the manufacture of the electrical apparatus. Homemade electric welding requires quite a lot of time during assembly. It is not so difficult as it is long and painstaking, requiring precise adherence to the calculated values. The procedure begins with the manufacture of a frame for the windings. For this, textolite plates of small thickness are used. Interior boxes should fit the transformer core with a small gap.
After assembling the two frames, it is necessary to insulate them to protect the electrical wire. This is done using any heat-resistant electrical insulating material (varnished fabric, glass tape or electrical cardboard).
A wire having heat-resistant insulation is wound onto the resulting frames. This will protect the product from possible breakdown due to overheating during operation. It is necessary to accurately count the number of turns so that there is no difference with the calculated values. Each wound layer is necessarily isolated from the next one. Reinforced insulation is placed between the primary and secondary winding layers. Do not forget to perform the necessary bends on the required number of turns. After winding is completed, external insulation is performed.
At the next stage, the wound windings are mounted on the transformer core, and it is laminated (assembled into a single structure). In this case, it is undesirable to drill sheets of transformer iron during installation. Metal plates are connected to checkerboard pattern and fit well. Assembling a simple U-shaped welding machine with your own hands is not particularly difficult. At the end of the assembly procedure, the integrity of the windings is checked for possible damage. The final stage is assembling the housing and connecting the electrical switching device. Additional equipment includes a rectifier unit, as well as an electric current regulator.
Be attentive to all processes, from calculations to assembly homemade welding. The final parameters of the manufactured device will depend on this.
A welding machine is a desirable acquisition for any household. The advantages of manual electric welding are obvious and indisputable: ease of use, a wide range of applications, high productivity and reliability of connections - and all this with the ability to work almost anywhere there is an electrical network. There seem to be no problems with choosing and purchasing welding machines today. A lot of household and professional industrial welding machines have appeared on sale. All kinds of handicraft workshops and craftsmen are vying with each other to offer their products. But the prices for factory-made devices “bite”, as a rule, several times, exceeding the current average monthly earnings. Basically, it is this sad discrepancy between one’s own income and price that always forces many people to take up welding with their own hands.
In modern literature you can find a lot of material on welding. In recent years, a number of articles devoted to the improvement and calculation of elements of welding transformers (ST) have been published in Radioamator, which undoubtedly indicates the interest of readers in this topic. I propose the most important thing: how and from what to make welding transformers at home. All the welding transformer circuits described below have been practically tested and are actually suitable for manual electric welding. Some of the schemes have been developed “among the people” for decades and have become a kind of “classic” of independent “transformer construction”.
Like any transformer, CT consists of primary and secondary (possibly with taps) windings wound on a large magnetic core made of transformer iron. The operating mode of the CT differs from a conventional transformer: it operates in arc mode, i.e. at almost maximum possible power. And hence strong vibrations, intense heating, and the need to use large-section wire. The CT is powered from a single-phase network of 220-240 V. The output voltage of the secondary winding in no-load mode (no load) (when no load is connected to the output) for homemade CTs is, as a rule, in the range of 45-50 V, less often up to 70 Q. In general, the output voltages for industrial welding machines are limited (80 V for AC, 90 V for DC). Therefore, large stationary units have an output of 60-80 V.
The main power characteristic of ST is considered to be the output current of the secondary winding in arc mode (welding mode). In this case, an electric arc burns in the gap between the end of the electrode and the metal being welded. The gap size is 0.5...1.1 d (d is the diameter of the electrode), it is maintained manually. For portable structures, operating currents are 40-200 A. The welding current is determined by the power of the welding machine. The choice of the diameter of the electrodes used and the optimal thickness of the metal being welded depend on the output current of the CT.
The most common are electrodes with steel rods D3 mm ("troika"), which require currents of 90-150 A (usually 100-130 A). In skillful hands, the “troika” will burn at 75 A. At currents greater than 150 A, such electrodes can be used for cutting metal (thin sheets of iron 1-2 mm can be cut at lower currents). When working with a D3 mm electrode, a current of 20-30 A (usually about 25 A) flows through the primary winding of the ST.
If the output current is lower than required, then the electrodes begin to “stick” or “glue”, welding their tips to the metal being welded: thus, the CT begins to work with dangerous overload in short circuit mode. At currents higher than permissible, the electrodes begin to cut the material: this can ruin the entire product.
For electrodes with an iron rod D2 mm, a current of 40-80 A (usually 50-70 A) is required. They can accurately weld thin steel 1-2 mm thick. Electrodes D4 mm work well at a current of 150-200 A. Higher currents are used for less common (D5-6 mm) electrodes and metal cutting.
In addition to power, an important property of the ST is its dynamic characteristics. The dynamic characteristics of the transformer largely determine the stability of the arc, and therefore the quality of the welded joints. Among the dynamic characteristics, we can distinguish steeply dipping and gently dipping. When manual welding, inevitable vibrations of the end of the electrode occur and, accordingly, a change in the arc burning length (at the moment of ignition of the arc, when adjusting the arc length, on uneven surfaces, from hand trembling). If the dynamic characteristic of the CT is steeply falling, then when the arc length fluctuates, minor changes in the operating current occur in the secondary winding of the transformer: the arc burns stably, the weld lies flat.
With a flat or rigid characteristic of the welding machine: when the length of the arc changes, the working current also changes sharply, which changes the welding mode - as a result, the arc burns unstably, the weld is of poor quality, and it is difficult or even impossible to work with such a welding machine manually. For manual arc welding, a steeply falling dynamic characteristic of the ST is required. Flat-fall type is used for automatic welding.
In general, in real conditions, it is hardly possible to somehow measure or quantify the parameters of the current-voltage characteristics, however, like many other parameters of the CT. Therefore, in practice, welding machines can be divided into those that weld better and those that work worse. When the ST works well, welders say: “It welds softly.” This should mean high quality of the weld, no metal spattering, the arc burns stably all the time, the metal is deposited evenly. All CT designs described below are actually suitable for manual arc welding.
The operating mode of the ST can be characterized as short-term repetitive. In real conditions, after welding, as a rule, installation, assembly and other work follows. Therefore, after operating in the arc mode, the CT has some time to cool in the cold mode. In the arc mode, the ST heats up intensely, and in the cold mode. It cools, but much more slowly. The situation is worse when CT is used for cutting metal, which is very common. In order to cut thick rods, sheets, pipes, etc. with an arc, when the current of a homemade transformer is not too high, you have to overheat the CT too much.
Any industrial device is characterized by such an important parameter as the operating duration coefficient (OL), measured in %. For domestic factory portable devices weighing 40-50 kg PR usually does not exceed 20%. This means that the CT can operate in the arc mode no more than 20% of the total time, the remaining 80% it should be in the idle mode. For most home-made designs, the PR should be taken even less. We will consider the intensive mode of operation of the ST to be one when the arc burning time is of the same order as the interruption time.
Self-made CTs are made according to different schemes: on U-, PU- and W-shaped magnetic cores: toroidal, with different combinations of winding arrangements. The manufacturing scheme of the CT and the number of turns of future windings are mainly determined by the available core - the magnetic circuit. In the future, the article will consider real schemes of homemade STs and materials for them. Now we will determine what winding and insulating materials will be needed for the future ST.
Given the high powers, relatively thick wire is used for the CT windings. Developing significant currents during operation, any CT gradually heats up. The heating rate depends on a number of factors, the most important of which is the diameter or cross-sectional area of the winding wires. The thicker the wire, the better it passes current, the less it heats up and, finally, the better it dissipates heat. The main characteristic is the current density (A/mm2): the higher the current density in the wires, the more intense the heating of the heating element occurs. Winding wires can be copper or aluminum. Copper allows you to use 1.5 times higher current density and heats up less: it is better to wind the primary winding with copper wire.
In industrial devices, the current density does not exceed 5 A/mm2 for copper wire. For homemade CT options, 10 A/mm2 for copper can be considered a satisfactory result. As the current density increases, the heating of the transformer sharply accelerates. In principle, for the primary winding you can use a wire through which a current with a density of up to 20 A/mm2 will flow, but then the CT will heat up to a temperature of 60 ° C after using 2 x 3 electrodes. If you think that you will have to weld a little, slowly, and you still don’t have the best materials, then you can wind the primary winding with wire and with a strong overload. Although this, of course, will inevitably reduce the reliability of the device.
In addition to the cross-section, another important characteristic of the wire is the insulation method. The wire can be varnished, wound in one or two layers of thread or fabric, which, in turn, are impregnated with varnish. The reliability of the winding, its maximum overheating temperature, moisture resistance, and insulating qualities greatly depend on the type of insulation (see Table 1).
Table 1
Note. PEV, PEM - wires enameled with high-strength varnish (viniflex and metalvin, respectively), produced with thin (PEV-1, PEM-1) and reinforced insulating layers (PEV-2, PEM-2); PEL - wire enameled with oil-based varnish; PELR-1, PELR-2 - wires enameled with high-strength polyamide varnish, respectively, with thin and reinforced layers of insulation; PELBO, PEVLO - wires based on PEL and PEV type wires with one layer, respectively, of natural silk, cotton yarn or lavsan; PEVTL-1, PEVTL-2 - wire enameled with high-strength polyurethane enamel, heat-resistant, with thin and reinforced layers of insulation; PLD - wire insulated with two layers of lavsan; PETV - wire enameled with heat-resistant high-strength polyester varnish; PSD type wires - with insulation made of alkali-free glass fiber, applied in two layers with gluing and impregnation with heat-resistant varnish (in brand designations: T - thinned insulation, L - with a surface varnish layer, K - with gluing and impregnation with silicone varnish); PETKSOT - wire insulated with heat-resistant enamel and fiberglass; PNET-imide is a wire insulated with high-strength polyamide-based enamel. The insulation thickness in the table is the difference between the maximum wire diameter and the nominal copper diameter.
The best insulation is made of fiberglass impregnated with heat-resistant varnish, but such wire is difficult to obtain, and if you buy it, it will not be cheap. The least desirable, but most accessible materials for homemade products are ordinary wires PEL, PEV Dtion. Such wires are the most common; they can be removed from the coils of chokes and transformers of used equipment. When carefully removing old wires from the coil frames, it is necessary to monitor the condition of their coating and additionally insulate slightly damaged areas. If the coils of wire were additionally impregnated with varnish, their turns are stuck together, and when you try to disconnect, the hardened impregnation often tears off its own varnish coating wires, exposing metal. In rare cases, in the absence of other options, “homemade workers” wind the primary windings even with a mounting wire in vinyl chloride insulation. Its disadvantages: excess insulation and poor heat dissipation.
The quality of laying the primary winding of the CT should always be given the greatest attention. The primary winding contains a larger number of turns than the secondary, its winding density is higher, and it heats up more. The primary winding is under high voltage; if it is shorted between turns or the insulation breaks down, for example, through moisture, the entire coil quickly “burns out”. As a rule, it is impossible to restore it without disassembling the entire structure.
The secondary winding of the CT is wound with a single or multi-core wire, the cross-section of which provides the required current density. There are several ways to solve this problem. First, you can use a monolithic wire with a cross section of 10-24 mm2 made of copper or aluminum.
Such rectangular wires (commonly called busbar) are used for industrial CTs. However, in most home-made designs, the winding wire has to be pulled many times through the narrow windows of the magnetic circuit. Try to imagine doing this about 60 times with 16mm2 solid copper wire. In this case, it is better to give preference to aluminum wires: they are much softer and cheaper.
The second method is to wind the secondary winding with a stranded wire of a suitable cross-section in ordinary vinyl chloride insulation. It is soft, easy to fit, and reliably insulated. True, the synthetic layer takes up excess space in the windows and interferes with cooling. Sometimes for these purposes they use old stranded wires in thick rubber insulation, which are used in powerful three-phase cables. The rubber is easy to remove, and instead of it, wrap the wire with a layer of some thin insulating material. The third method is to make a secondary winding from several single-core wires approximately the same as those used to wind the primary winding. To do this, 2-5 wires D1.62.5 mm are carefully tied together with tape and used as one stranded wire. This bus of several wires takes up a small volume and is sufficiently flexible, which makes it easy to install.
If the required wire is difficult to obtain, then the secondary winding can be made from thin, most common PEV, PEL wires D0.5-0.8 mm, although this will take an hour or two. First, you need to choose a flat surface, where you will rigidly install two pegs or hooks with a distance between them equal to the length of the secondary winding wire of 2030 m. Then stretch several dozen strands of thin wire between them without bending, you will get one elongated bundle. Next, disconnect one of the ends of the beam from the support and clamp it into the chuck of an electric or hand drill. At low speeds, the entire bundle is slightly taut and twists into a single wire. After twisting, the length of the wire will decrease slightly. At the ends of the resulting stranded wire, you need to carefully burn the varnish and clean the ends of each wire separately, and then solder everything securely together. After all, it is advisable to insulate the wire by wrapping it along its entire length with a layer of, for example, adhesive tape.
To lay the windings, fasten the wire, inter-row insulation, insulate and fasten the magnetic circuit, you will need a thin, strong and heat-resistant insulating material. In the future, it will be seen that in many CT designs the volume of magnetic circuit windows, into which it is necessary to lay several windings with thick wires, is greatly limited. Therefore, in this “vital” space of the magnetic circuit, every millimeter is valuable. With small core sizes, insulating materials should occupy as little volume as possible, i.e. be as thin and elastic as possible. The common PVC iso1.6-2.4 mm in simple varnish insulating tape can be immediately excluded from use on heating areas of the heating system. Even with slight overheating, it becomes soft and gradually spreads or is pressed through by wires, and with significant overheating it melts and foams. For insulation and bandage, you can use fluoroplastic, glass... and varnished fabric keeper tapes, and regular tape between the rows.
Scotch tape can be considered one of the most convenient insulating materials. After all, having an adhesive surface, small thickness, elasticity, it is quite heat-resistant and strong. Moreover, now adhesive tape is sold almost everywhere on reels of various widths and diameters. Small-diameter coils are ideally suited for pulling compact magnetic cores through narrow windows. Two or three layers of tape between the rows of wire practically do not increase the volume of the coils.
And finally, the most important element of any ST is the magnetic circuit. As a rule, for homemade products, magnetic cores of old electrical appliances are used, which previously had nothing in common with ST, for example, large transformers, autotransformers (LATRs), electric motors. The most important parameter of the magnetic circuit is its cross-sectional area (S), through which the flux circulates magnetic field.
Magnetic cores with a cross-sectional area of 25-60 cm2 (usually 30-50 cm2) are suitable for the manufacture of CT. The larger the cross-section, the greater the flux the magnetic circuit can transmit, the greater the power reserve the transformer has, and the fewer turns its windings contain. Although the optimal cross-sectional area of the magnetic circuit, when a medium-power ST has the best characteristics, is 30 cm2.
There are standard methods for calculating the parameters of the magnetic core and windings for industrially manufactured CT circuits. However, these methods are practically not suitable for homemade products. The fact is that the calculation according to the standard methodology is carried out for a given power of the ST, and only in a single option. They calculate it separately optimal value cross-section of the magnetic circuit and number of turns. In fact, the cross-sectional area of the magnetic circuit for the same power can be within very wide limits.
There is no connection between an arbitrary section and turns in the standard formulas. For homemade CTs, any magnetic cores are usually used, and it is clear that it is almost impossible to find a core with “ideal” parameters of standard methods. In practice, it is necessary to select winding turns to match the existing magnetic circuit, thereby setting the required power.
The power of the CT depends on a number of parameters, which are impossible to fully take into account under normal conditions. However, the most important among them are the number of turns of the primary winding and the cross-sectional area of the magnetic circuit. The relationship between the area and the number of turns will determine the operating power of the ST. To calculate CT intended for D3-4 mm electrodes and operating from a single-phase network with a voltage of 220-230 V, I propose to use the following approximate formula, which I obtained based on practical data. Number of turns N=9500/S (cm2). At the same time, for ST with a large magnetic core area (more than 50 cm2) and relatively high efficiency, it can be recommended to increase the number of turns calculated by the formula by 10-20%.
For CTs manufactured on cores with a small area (less than 30 cm), on the contrary, it may be necessary to reduce the number of design turns by 10-20%. In addition, the useful power of the CT will be determined by a number of factors: efficiency, voltage of the secondary winding, supply voltage in the network... (Practice shows that the network voltage, depending on the area and time, can fluctuate between 190-250 V).
The resistance of the power line is also important. Comprising only a few ohms, it has virtually no effect on the readings of the voltmeter, which has a high resistance, but can greatly dampen the power of the CT. The influence of line resistance can be especially noticeable in places remote from transformer substations (for example, dachas, garage cooperatives, in rural areas where lines are laid with thin wires with a large number of connections). Therefore, initially it is hardly possible to accurately calculate the output current of the CT for different conditions - this can only be done approximately. When winding the primary winding, it is better to make its last part with 2-3 taps every 20-40 turns. Thus, you can adjust the power by choosing the best option for yourself, or adapt to the mains voltage. To obtain higher powers from the CT, for example, to operate a D4 mm electrode at currents greater than 150 A, it is necessary to further reduce the number of turns of the primary winding by 20-30%.
But it should be remembered that with increasing power, the current density in the wire also increases, and therefore the intensity of heating of the windings. The output current of the CT can also be slightly increased by increasing the number of turns of the secondary winding, so that the output voltage is cold. increased from the estimated 50 V to higher values (70-80 V).
Having connected the primary winding to the network, it is necessary to measure the cold current, it should not have a large knowledge (0.1-2 A). (When the CT is connected to the network, a short-term but powerful current surge occurs). In general, in terms of current x.x. it is impossible to judge the output power of a CT: it can be different even for the same types of transformers. However, having examined the current dependence curve x.x. from the CT supply voltage, one can more confidently judge the properties of the transformer.
Fig.1
To do this, the primary winding of the CT must be connected through LATR, which will allow the voltage on it to be smoothly changed from 0 to 250 V. The current-voltage characteristics of the CT in no-load mode with different numbers of turns of the primary winding are shown in Fig. 1, where 1 - the winding contains little turns; 2 - ST operates at its maximum power; 3, 4 - moderate power ST. At first, the current curve gently, almost linearly increases to a small value, then the rate of increase increases - the curve smoothly bends upward, followed by a rapid increase in current. When the current tends to infinity up to the operating voltage point of 240 V (curve 1), this means that the primary winding contains few turns, and it must be wound up (it must be taken into account that the ST, switched on at the same voltage without LATR, will consume a current of approximately 30% more). If the operating voltage point lies at the bend of the curve, then the CT will produce its maximum power (curve 2, welding current of the order of 200 A). Curves 3 and 4 correspond to the case when the transformer has a power resource and an insignificant cold current: most homemade products are focused on this case. Really currents x.x. are different for different types of CT: most lie in the range of 100-500 mA. I do not recommend installing current x.x. more than 2 A.
After getting acquainted with the general issues of manufacturing homemade welding transformers, we can move on to a detailed consideration of actually existing CT designs, the features of their manufacture and materials for them. I assembled almost all of them with my own hands or took direct part in their production.
Welding transformer on a magnetic core from LATR
A common material for the manufacture of homemade welding transformers (WT) has long been burnt LATRs (laboratory autotransformer). Those who have dealt with them know well what it is. As a rule, all LATRs have approximately the same appearance: a well-ventilated round tin body with a tin or ebonite front cover with a scale from 0 to 250 V and a rotating handle. Inside the case there is a toroidal autotransformer made on a magnetic core of large cross-section. It is this magnetic core that will be needed from LATR for the manufacture of a new ST. Usually, two identical magnetic core rings from large LATRs are required.
LATRs were produced in different types with a maximum current from 2 to 10 A. Only those STs are suitable for production, the dimensions of the magnetic cores of which allow the required number of turns to be laid. The most common among them is probably the LATR 1M autotransformer, which, depending on the winding wire, is designed for a current of 6.7-9 A, although this does not change the dimensions of the autotransformer itself. The LATR 1M magnetic core has the following dimensions: outer diameter D=127 mm; internal diameter d=70 mm; ring height h=95 mm; cross section S=27 cm2 and mass about 6 kg. From two rings from LATR 1M you can make a good ST, however, due to the small internal volume of the window, you cannot use too thick wires and you will have to save every millimeter of window space.
There are LATRs with larger magnetic conductor rings, for example RNO-250-2 and others. They are better suited for making CT, but are less common. For other autotransformers similar in parameters to LATR 1M, for example AOSN-8-220, the magnetic core has a larger outer diameter of the ring, but a smaller height and window diameter d = 65 mm. In this case, the window diameter must be expanded to 70 mm. The magnetic circuit ring consists of pieces of iron tape wound on each other, secured at the edges by spot welding.
In order to increase the internal diameter of the window, you should disconnect the end of the tape from the inside and unwind the required amount. But don't try to rewind in one go. It is better to unwind one turn at a time, cutting off the excess each time. Sometimes the windows of larger LATRs are expanded in this way, although this inevitably reduces the area of the magnetic circuit.
At the beginning of the manufacture of the CT, it is necessary to insulate both rings. Pay special attention to the corners of the edges of the rings - they are sharp and can easily cut the applied insulation and then short-circuit the winding wire. It is better to apply some kind of strong and elastic tape lengthwise to the corners, for example, a thick keeper tape or a cambric tube cut lengthwise. On top of the rings (each separately) is wrapped with a thin layer of fabric insulation.
Next, the isolated rings are connected together (Fig. 2). The rings are tightly tightened with strong tape, and fixed on the sides with wooden pegs, also then tied with electrical tape; the core magnetic circuit for the ST is ready.
The next step is the most important - laying the primary winding. The windings of this CT are wound according to the scheme (Fig. 3) - the primary is in the middle, two sections of the secondary are on the side arms. “Experts” who know this type of transformer often call it “ushastik” in a peculiar jargon because of the round “Cheburashka ears” protruding in different directions of the sections of the secondary winding.
The primary takes about 70-80 m of wire, which will have to be pulled through both windows of the magnetic circuit with each turn. In this case, there is no way to do without a simple device (Fig. 4). First, the wire is wound on a wooden reel and in this form is pulled through the windows of the rings without any problems. The winding wire can consist of pieces (even ten meters long) if you can only get one. In this case, it is wound in parts, and the ends are connected to each other. To do this, the tinned ends are connected (without twisting) and fastened with several turns of thin copper core without insulation, then finally soldered and insulated. This connection does not crack the wire and does not take up a large volume.
The diameter of the primary winding wire is 1.6-2.2 mm. For magnetic cores made up of rings with a window diameter of 70 mm, you can use a wire with a diameter of no more than 2 mm, otherwise there will be little space left for the secondary winding. The primary winding contains, as a rule, 180-200 turns at normal mains voltage.
So, let’s assume that in front of you is an assembled magnetic circuit, the wire is prepared and wound on a reel. Let's start winding. As always, we put a cambric on the end of the wire and tighten it with electrical tape to the beginning of the first layer. The surface of the magnetic circuit has a rounded shape, so the first layers will contain fewer turns than subsequent ones - to level the surface (Fig. 5).
The wire should be laid turn to turn, in no case allowing wire to overlap wire. The layers of wire must be insulated from each other. (During operation, the CT vibrates strongly. If wires in varnish insulation lie on top of each other without intermediate insulation, then as a result of vibration and friction against each other, the varnish layer may be destroyed and a short circuit will occur). To save space, the winding should be laid as compactly as possible. On a magnetic circuit made of small rings, the interlayer insulation should be used thinner.
Small rolls of adhesive tape are well suited for these purposes; they easily fit into filled windows, and the adhesive tape itself does not take up excess space. You should not try to wind the primary winding quickly and in one go. This process is slow, and after laying the hard wires, your fingers begin to hurt. It’s better to do this in 2-3 approaches - after all, quality is more important than speed.
Once the primary winding is made, most of the work is done. Let's deal with the secondary winding. Let us determine the number of turns of the secondary winding for a given voltage. To begin with, let’s connect the ready-made primary winding to the network. Current x.x. This version of the CT is small - only 70-150 mA, the hum of the transformer should be barely audible. Wind 10 turns of any wire onto one of the side arms and measure the output voltage on it.
Each of the side arms accounts for half of the magnetic flux created on the central arm, so here each turn of the secondary winding accounts for 0.6-0.7 V. Based on the result obtained, calculate the number of turns of the secondary winding, focusing on a voltage of 50 V ( about 75 turns).
The choice of secondary winding material is limited by the remaining space of the magnetic circuit windows. Moreover, each turn of a thick wire will have to be pulled along its entire length into a narrow window, and no amount of “automation” will, alas, help here. I have seen transformers made on LATR 1M rings, into which craftsmen, using a hammer and their own patience, pushed a thick monolithic copper wire with a cross-section of twenty square meters.
Another thing is that if you are new to this business, then you should not tempt fate by unwinding solid copper back as difficult as winding it. Easier to wind aluminum wire cross section 16-20 mm2. The easiest way is to wind it with ordinary 10 mm2 stranded wire in synthetic insulation - it is soft, flexible, well insulated, but will heat up during operation. You can make a secondary winding from several strands of copper wire, as described above. Wrap half the turns on one arm, half on the other (Fig. 3). If there are no wires of sufficient length, you can connect them from pieces - no problem. Having wound the windings on both arms, you need to measure the voltage on each of them, it can differ by 2-3 V - the slightly different properties of the magnetic cores of different LATRs affect it, which does not particularly affect the properties of the ST. Then the windings on the arms are connected in series, but you need to make sure that they are not in antiphase, otherwise the output voltage will be close to 0. With a network voltage of 220-230 V, the CT of this design should develop a current in arc mode of 100-130 A, at in a short circuit, the secondary circuit current is up to 180 A.
It may turn out that it was not possible to fit all the calculated turns of the secondary winding into the windows, and the output voltage turned out to be lower than required. The operating current will decrease slightly. To a greater extent, the decrease in cold voltage. affects the arc ignition process. The arc ignites easily at an idle voltage close to 50 V and above, although the arc can be ignited at lower voltages without any problems. I had the opportunity to work with ST with x.x output. 37 V AC, and the quality was quite satisfactory. So if the manufactured CT has an output voltage of 40 V, then it can be used for work. It’s another matter if you come across electrodes designed for high voltages - some brands of electrodes operate from 70-80 V.
On rings from LATRs, it is also possible to make ST according to a toroidal scheme (Fig. 6). For this you also need two rings, preferably from large LATRs. The rings are connected and insulated: one ring-magnetic core with a significant area is obtained. The primary winding contains the same number of turns, but it is wound along the length of the entire ring and, as a rule, in two layers. The problem of the lack of internal space in the magnetic circuit window of such a ST circuit is even more acute than for the previous design. Therefore, it is necessary to insulate with as thin layers and materials as possible. Thick winding wires (recommended for the primary winding D1.8 mm) should not be used. In some installations, LATRs of especially large sizes are used; only on one ring of this type can a toroidal CT be made.
The advantageous difference between the ST toroidal circuit is enough high efficiency. Each turn of the secondary winding accounts for more than 1 V of voltage, therefore, the “secondary” will have fewer turns, and the output power will be higher than in the previous circuit. However, the length of the turn on a toroidal magnetic circuit is longer, and it is unlikely that it will be possible to save on wire here. The disadvantages of this scheme include the complexity of winding, the limited volume of the window, the inability to use large-section wire, and also the high heating intensity. If in the previous version all windings were located separately and at least partially had contact with air, now the primary winding is completely under the secondary, and their heating is mutually reinforcing.
It is difficult to use rigid wires for the secondary winding. It is easier to wind it with soft stranded or multi-core wire. If you select all the wires correctly and carefully lay them out, then the required number of turns of the secondary winding will fit into the space of the magnetic circuit window, and the required voltage will be obtained at the CT output. The arc burning characteristic of the toroidal CT can be considered better than that of the previous transformer.
Sometimes a toroidal ST is made from several rings of LATRs, but they are not placed on top of each other, but the iron strips of the tape are rewound from one to another. To do this, first, the inner turns of the strips are selected from one ring to expand the window. The rings of other LATRs are completely unraveled into strips of tape, which are then wound as tightly as possible around the outer diameter of the first ring. After this, the assembled single magnetic circuit is wound very tightly with insulating tape. Thus, a ring-magnetic core is obtained with a more voluminous internal space than all previous ones. This can accommodate a wire of significant cross-section, and it is much easier to do. The required number of turns is calculated based on the cross-sectional area of the assembled ring. The disadvantages of this design include the complexity of manufacturing the magnetic circuit. Moreover, no matter how hard you try, you still won’t be able to manually wind the iron strips around each other as tightly as before. As a result, the magnetic circuit turns out to be flimsy. When the ST operates, the iron in it vibrates strongly, producing a powerful hum.
Sometimes the “original” windings of LATRs burn out only on one edge on the down conductor path or remain unharmed at all. Then there is a temptation to save yourself the extra effort and use a ready-made, perfectly laid primary winding of one ring. Practice shows that, in principle, this idea can be realized, however, the benefit from such an undertaking will be minimal. The LATR 1M winding has 265 turns of wire with a diameter of 1 mm. If you wind the secondary directly onto it, the transformer will develop excessive power, quickly heat up and fail. After all, in reality, the “native” winding of the LATR can operate at low power - only for D2 mm electrodes, which require a current of 50-60 A. Then a current of about 15 A should flow through the primary winding of the transformer.
For such power, the primary winding of a ST from one LATR should contain about 400 turns. They can be wound up by first varnishing the conductor path and insulating the original winding of the LATR. You can do it another way: do not wind the turns, but extinguish the power with a ballast resistor connected to the circuit of the primary or secondary winding. As an active resistance, you can use a battery of parallel-connected powerful wire resistors, for example PEV50...100, with a total resistance of 10-12 Ohms, connected to the primary winding circuit. During operation, resistors become very hot; to avoid this, they can be replaced with a choke (reactance). Wind the inductor on the frame of a 100-200-watt transformer with a number of turns of 200-100. Although the ST will have significantly best characteristic, if a ballast resistor (hundredths of an ohm) is connected at the output of the secondary winding. To do this, use a piece of thick, high-resistance wire wound into a spiral, the length of which should be selected experimentally.
Some devices used LATRs of especially large sizes; only on one ring of this type can a full-fledged ST be wound. In the designs described above, it was necessary to use two rings: this was done not so much because of the need to increase the area of the magnetic circuit, but to reduce the number of turns, otherwise they simply would not fit in narrow windows. In principle, a cross-sectional area and one ring are sufficient for a ST: it would have even better characteristics, since the magnetic flux density would be closer to optimal. But the problem is that smaller magnetic cores inevitably require more turns, which increases the volume of the coils and requires more window space.
Welding transformer on a magnetic core from the stator of an electric motor
From LATRs, let's move on to the next common source for obtaining good magnetic cores for ST. Often, toroidal CTs are wound on magnetic guide material taken from a failed large asynchronous three-phase electric motor, which are most common in industry. Motors with a power of close to 4 kV A or more are suitable for the manufacture of ST.
The electric motor consists of a rotor rotating on a shaft and a stationary stator pressed into a metal motor housing, which are connected by two side covers tightened together with pins. Only the stator is of interest. The stator consists of a set of iron plates - a round magnetic circuit with windings installed on it. The shape of the stator magnetic circuit is not completely circular, with inside it has longitudinal grooves into which the motor windings are placed.
Different brands of engines, even of the same power, may have stators with different geometric dimensions. For the manufacture of STs, those with a larger body diameter and correspondingly shorter length are better suited.
The most important part in the stator is the magnetic ring. The magnetic core is pressed into a cast iron or aluminum motor housing. Wires that need to be removed are tightly packed into the grooves of the magnetic circuit.
It is better to do this when the stator is still pressed into the housing. To do this, on one side of the stator, all winding outputs are cut off to the end with a sharp chisel. The wire should not be cut on the opposite side - there the windings form something like loops, through which you can pull out the remaining wires. Using a pry bar or a powerful screwdriver, pry up the bends of the wire loops and pull out several wires at a time. The end of the engine housing serves as a stop, creating a lever. The wires come out easier if you burn them first.
You can burn blowtorch, directing the jet strictly along the groove. Care must be taken not to overheat the stator iron, otherwise it will lose its electrical properties. The metal body can then be easily destroyed - a few blows from a good hammer and it will crack - the main thing is not to overdo it.
If the motor magnetic circuit ring is fastened and separated from the windings and housing, then it is tightly insulated as usual. Sometimes you can hear that the remaining grooves of the windings need to be filled with iron, supposedly to increase the area of the magnetic circuit. This must not be done under any circumstances: otherwise the properties of the transformer will deteriorate sharply, it will begin to consume an excessively large current, and its magnetic circuit will become very hot even in idle mode.
The stator ring has impressive dimensions: the internal diameter is about 150 mm, so you can install a wire of a significant cross-section without worrying about space.
The cross-sectional area of the magnetic circuit periodically changes along the length of the ring due to the grooves: inside the groove its value is much smaller. It is this smaller value that one should focus on when calculating the number of turns of the primary winding (Fig. 7).
As an example, I will give the parameters of a real-life ST made from an electric motor stator. It was used for asynchronous motor power 4.18 kVA with an internal diameter of the magnetic circuit ring of 150 mm, an external one of 240 mm and a magnetic circuit ring height of 122 mm. The effective cross-sectional area of the magnetic circuit is 29 cm2. The set of magnetic circuit plates was not initially fastened, so it had to be welded with eight longitudinal seams along the outside of the ring. Any explicit negative consequences, associated with Foucault currents, as we feared, the welds did not cause. The primary winding of the toroidal CT has 315 turns of copper wire with a diameter of 2.2 mm, the secondary is designed for a voltage of 50 V. The primary winding is wound in more than two layers, the secondary is laid 3/4 of the length of the ring. ST in arc mode develops a current of about 180-200 A at a supply voltage of 230 V.
When winding the secondary winding of a toroidal CT, it is advisable to lay it so that it does not overlap the last part of the primary, then the primary winding can always be wound or unwinded during the final adjustment of the CT.
Such a transformer can also be wound with windings spaced apart on different arms (Fig. 8). In this case, you always have access to each of them.
Welding transformer from television transformers
All the welding transformer designs described above have common disadvantages: the need to wind the wire, each time pulling the turns through the window, as well as a shortage of magnetic core material - after all, not everyone can get rings from LATR or a suitable stator from an electric motor. Therefore, I developed and manufactured a CT of my own design, which does not require scarce materials. It does not have these disadvantages and is easy to implement at home. The starting material for this design is a very common material - parts from television transformers.
Old domestic color TVs used large, heavy network transformers, for example, TS-270, TS-310, ST270. These transformers have U-shaped magnetic cores; they can be easily disassembled by unscrewing just two nuts on the tie rods, and the magnetic core splits into two halves. For older transformers TS-270, TS-310, the cross-section of the magnetic core has dimensions of 2x5 cm, S = 10 cm2, and for the newer TS-270, the cross-section of the magnetic core has dimensions of 2.5x4.5 cm. The window width of old transformers is several millimeters larger.
Older transformers are wound with copper wire; a wire with a diameter of 0.8 mm may be useful from their primary windings.
New transformers are wound with aluminum wire. Today, this stuff is migrating en masse to landfills, so problems with their acquisition are unlikely to arise. Several old or burnt-out transformers can be purchased inexpensively at any television repair shop. It is their magnetic cores (together with their frames), with minor alterations, that can be used for the manufacture of ST. For ST you will need three identical transformers from TVs, and the total area of their combined magnetic circuit will be 30-34 cm2. How to connect them together is shown in Fig. 9, where 1,2,3 are magnetic cores with frames from television transformers. Three separate U-shaped cores are connected with their ends facing each other and tightened with the same frame clamps. In this case, the parts protruding beyond the end metal frames it is necessary to trim: on the central magnetic circuit on both sides, on the side ones - only on one inner side.
The result is a single magnetic core with a large cross-section, which is easy to assemble and disassemble. When disassembling television transformers, it is necessary to immediately mark the adjacent sides of the magnetic cores so that during assembly the halves of different cores are not mixed up. They must fit in exactly the same position as they were assembled at the factory.
The volume of the window of the resulting magnetic circuit allows the use of a wire up to 1.5 mm in diameter for the primary winding, and for the secondary bus - a rectangular cross-section of 10 mm2 or a stranded wire made from a bundle of thin wires with a diameter of 0.6-0.8 mm of the same cross-section. This, of course, is not enough for a full-fledged ST; however, it justifies itself in cases of short-term work, given the low costs of manufacturing this design.
The windings are wound on cardboard frames separately from the magnetic core. A cardboard frame can be made from a pair of “original” transformer frames by removing the side cheeks from one narrow side, and instead, the wide cheeks can be glued together using additional strips of hard cardboard. When winding inside cardboard frames, be sure to tightly insert several scraps of wooden planks, but not just one, otherwise the winding will compress it and it will not come out again. The windings must be laid turn to turn as tightly as possible. On the outside, after the first layer of wire and then every two, it is necessary to insert wooden inserts (Fig. 10) to provide gaps and ventilation of the windings.
It is best to make the secondary winding from a 10 mm2 rectangular busbar, so it will take up the least volume. If you don’t have a bus, and you decide to make a secondary winding wire from a bunch of thin wires lying around, as described above, then be prepared for possible difficulties with its installation. In the case of a multi-core wire of the secondary winding, it may turn out that it does not “fit” into the required volume of the frame: mainly due to the warping of the spring coils, and it is better to tighten them, as the frame will collapse. In this case, you will have to abandon the cardboard frame altogether.
The secondary winding must be wound onto the already assembled magnetic circuit with the primary winding coil installed, pulling each turn through the window. On a rigid magnetic circuit flexible wire It will be possible to tighten it much more tightly than on a cardboard frame, and a larger number of turns will fit into the window.
When assembling the magnetic circuit special attention attention should be paid to the reliability of fastening and tight fit of the individual halves of the PU-shaped core. As already mentioned, the mating halves of the magnetic core must be from the same transformers and installed on the same sides as at the factory. Under the nuts of the tie rods, it is imperative to place large-diameter washers and washers. On my ST, the primary winding contains 250 turns of varnished wire with a diameter of 1.5 mm, the secondary winding contains 65 turns of stranded wire with a cross-section of 10 mm2, which provides an output of 55 V at a mains voltage of 230 V. With such data, the no-load current is 450 mA; current in arc mode in the secondary circuit is 60-70 A; The arc burning performance is good. It is assembled on the basis of ST-270 parts. The welding transformer is used to work with an electrode with a diameter of 2 mm; the “troika” also burns steadily but weakly on it.
The advantages of this type of ST are the ease of manufacture and the abundance of materials for it. The main disadvantage is the imperfection of the magnetic circuit, which has a compressed gap between the two halves. During factory production of transformers of this type, the gaps in the magnetic circuit are filled with a special filler. At home, they have to be pulled together “dry”, which, of course, worsens the performance and efficiency of the transformer. It is not possible to install thick wires in a small window, which greatly reduces the operating life of the CT. It should be noted that the primary winding of this ST heats up more than, for example, the winding with the same wire of a ST on LATRs - “ushastik”. This is affected, firstly, by the large number of turns of windings and, probably, by the imperfection of the magnetic system of the transformer. Nevertheless, ST can be successfully used for auxiliary purposes, especially for welding thin automotive metal. It is distinguished by its particularly compact dimensions and low weight - 14.5 kg.
Other types of welding transformers
In addition to special production, ST can be obtained by converting ready-made transformers for various purposes. Powerful transformers of a suitable type are used to create networks with a voltage of 36, 40 V, usually in places with increased fire hazard, humidity and for other needs. For these purposes they use different types transformers: different powers, connected to 220, 380 V according to a single or three-phase circuit. The most powerful of the portable types usually have a power of up to 2.5 kVA. The wire and iron of such transformers are selected according to power, based on long-term operation (current density 2-4 A/mm2), so they have large cross-sections. In arc welding mode, the transformer is capable of developing power several times higher than the rated one, and its wire fearlessly withstands short-term current overloads.
If you have a powerful single-phase transformer with terminals for 220/380 V and a 36 V output (possibly 12 V), then there are no problems with connecting it. You may have to wind up a few turns of the secondary winding to increase the output voltage. Transformers with a primary winding wire diameter of about 2 mm and a magnetic core area of up to 60 cm2 are suitable.
There are transformers with a voltage of 36 V, designed for inclusion in a three-phase network of 380 V. Transformers with a power of 2.5 kVA are well suited for conversion, and transformers with a power of 1.25 and 1.5 kVA can only be used in short-term mode, since their windings quickly overheat under significant overloads.
To use three-phase transformers from a single-phase 220 V network, their windings must be connected to each other differently. Then, with good network voltage, the power of the resulting CT will be sufficient to operate with a D4 mm electrode.
Three-phase transformers were manufactured on a W-shaped magnetic core with a cross-section of one arm of at least 25 cm2 (Fig. 11).
There are two windings wound on each arm - the primary inside and the secondary on top of it. Thus, the transformer has six windings. First you need to disconnect the windings from the previous circuit and find the beginning and end of each. In this case, the middle arm coils will not be needed; only the windings on the outer arms will work. The two primary windings from the outermost shoulders must be connected to each other in parallel. Due to the fact that the magnetic flux must circulate in the magnetic circuit in one direction, the coils on opposite arms must create fluxes in opposite directions relative to, for example, the axis of the central arm: one up, the other down. Since the coils are wound in the same way, the currents in them must flow in opposite directions. This means that they need to be connected in parallel with different ends: the beginning of the 1st should be connected to the end of the 2nd, the end of the 1st to the beginning of the 2nd (Fig. 12).
The secondary windings are connected in series with each other at ends or beginnings (Fig. 12). If the windings are connected correctly, then the output voltage is x.x. should not be much higher than 50 V.
Transformers of this type are often built into a convenient metal housing with handles and a hinged lid. Converting them into welding machines is very common.
Most industrial single-phase transformers are made according to a U-shaped circuit, the magnetic circuit of which is assembled from a set of rectangular plates of the appropriate length and width. The windings on the U-shaped magnetic core can be arranged in two options: in the first (Fig. 13, a) the transformer has a high efficiency, in the second (Fig. 13, b) the transformer is easier to manufacture, and then, if necessary, add or remove some the number of turns in an already assembled transformer. In this case, the transformer is easier to repair, since only one winding burns out, and the second usually remains intact. When using the circuit (Fig. 13, a), when one winding catches fire, the second one is always charred.
If you have suitable transformer iron plates, then it is easy to make a ST on a U-shaped magnetic circuit yourself. The windings are wound separately onto the frame, and then installed on the assembled magnetic circuit. The easiest way to see how a U-shaped magnetic circuit is assembled is by disassembling any small transformer of a similar design. In large transformers, the plates are installed not one at a time, but in packs of 3-4 pieces, this is faster.
The magnetic core for CT can be used, for example, from U-shaped transformers removed from old equipment, if they have sufficient window volume and magnetic core cross-section. But, as a rule, most instrument transformers have limited dimensions. It makes sense to assemble one magnetic core from two identical transformers, thus increasing the cross-sectional area. Increasing the cross-section of the magnetic circuit results in a gain in turns: they will now have to be wound significantly less. And the fewer turns, the smaller the window volume you can install the windings. A reasonable limit is 5060 cm2.
CT can be made on a W-shaped magnetic core, provided that the required number of turns of thick winding wires fit into its windows. The author made a ST from the magnetic cores of two identical W-shaped transformers with the external dimensions of the W-shaped plate being 122x182 mm and the window dimensions being 31x90 mm. The cross-sectional area of the magnetic circuit folded from a set of plates from two transformers exceeded 60 cm2, which made it possible to reduce the number of turns of its windings to a minimum. A primary winding of 176 turns of wire D1.68 mm and a secondary winding of two wires D2.5 mm with an output voltage of 46 V entered end-to-end. With a mains voltage of 235 V, the ST developed an arc current of 160 A, although it heated up more than we would like.. .
As a rule, the cores of industrial transformers made of plates can be easily disassembled: removing the old wires and winding new windings is not difficult. Sometimes it makes sense to first install a secondary winding (low voltage) on the W-shaped magnetic core, and on top of it a primary (high voltage). This does not deteriorate the characteristics of the ST, but many problems can be avoided. The number of turns of the secondary winding can be very approximate, oriented at 40-60 V. You will have to select the turns of the primary winding when adjusting the CT to the required power. So, having first calculated and laid out the low voltage winding, focusing on approximately 50 V, then you can always remove or add a certain number of turns from the upper primary winding of the finished CT.
Quite powerful and large transformers can be found in units and equipment that have served their time.
For stationary transformers, the extreme capabilities of either iron or winding wires are never used - everything is done with a reserve. Wires often have large cross-sections, since they are designed for a current density 3-4 times less than that allowed for ST. Very often large transformers have many secondary windings designed for different voltages and powers. There is always one primary winding in a transformer, and its wire is designed to carry full power. In this case, you can leave the primary winding completely or partially unwind, and remove all the secondary windings by winding one thick wire in their place. If the primary winding is also unsuitable, but the magnetic circuit itself is suitable for making CT, then you will have to wind all the windings.
Equipment often uses low voltages - 12; 27 V. Therefore, powerful transformers wound with thick wire can have an output of 2x12 V, 27 V and others, which are clearly insufficient for use as CT. If there are two such transformers, then they can be combined, without alteration, into one welding one. To do this, the primary windings are connected in parallel, and the secondary windings are connected in series, and their voltages are summed.
It may turn out that such a combined ST will have a poor, close to hard, characteristic. To correct the characteristic, it is necessary to include in the secondary winding circuit, in series with the arc, a ballast resistance - a piece of nichrome or other high-resistance wire. Having a resistance of the order of hundredths of an ohm, it will somewhat reduce the power of the CT, but will allow you to work in manual mode.
Adjusting the current of the welding transformer
An important design feature of any welding machine is the ability to adjust the operating current.
There are various ways to regulate the CT current. The easiest way to wind the windings is to make them with taps and, by switching the number of turns, change the current. However, this method can only be used to adjust the current rather than to regulate it over a wide range. After all, in order to reduce the current by 2-3 times, you will have to increase the number of turns of the primary winding too much, which will inevitably lead to a voltage drop in the secondary circuit.
Used in industrial devices different ways current regulation: shunting using chokes of various types; change in magnetic flux due to the mobility of windings or magnetic shunting, etc.; use of active ballast resistance stores and rheostats; the use of thyristor, triac and other electronic circuits power regulation. Most industrial power control schemes are too complex for full implementation on homemade CTs. Let's look at simplified methods that are actually used in homemade implementation.
Recently, thyristor and triac power control circuits have become somewhat widespread.
Typically, a triac is included in the primary winding circuit; a thyristor can only be used at the output. Power regulation occurs by periodically turning off the primary or secondary winding of the CT for a fixed period of time at each half-cycle of the current; the average current value decreases. Naturally, the current and voltage after this do not have a sinusoidal shape. Such circuits allow you to regulate power over a wide range. A person who understands radio electronics can make such a circuit on his own, although this is very difficult.
In different magazines you can find many very simple circuits with the same operating principle, consisting of only a few parts. They are intended mainly for adjusting the intensity of light bulbs and electric heating devices. These circuits are of little use as power regulators for ST. Most of them operate unstable: their scales are not linear, and the calibration changes with changes in the network voltage, the current through the thyristor gradually increases during operation due to heating of the circuit elements, in addition, the output power of the CT is usually greatly suppressed even at the maximum unlocking position of the regulator.
Don’t be surprised if, when you connect a triac circuit to the primary winding, the CT begins to “knock” already at idle. This knock can be heard in the literal sense of the word, and from STs who had previously worked at dry gas. almost silent. This is not surprising, because with each unlocking of the triac there is an instantaneous increase in voltage, causing powerful short-term pulses of self-induction EMF and surges in current consumption. Industrial devices, wound with thick wire in reliable insulation, tolerate this power supply flaw without any consequences. For "frail" homemade designs, I would not recommend using a triac on the primary winding.
For homemade designs, it is better to use a triac or thyristor regulator in the secondary winding circuit. This will relieve the ST from unnecessary loads. Almost the same circuit is suitable for this, but with a more powerful device, although the arc burning process is somewhat worse when using regulators of this type. After all, now, as the power decreases, the arc begins to burn in separate, increasingly short-term flashes. This method of adjusting the current, due to the complexity of manufacturing and low reliability, has not become widespread for homemade CTs.
The most widespread I got a very simple and reliable way to regulate the current using a ballast resistance connected at the output of the secondary winding. Its resistance is on the order of hundredths, tenths of an ohm, and it is selected experimentally.
For these purposes, powerful resistance wires have long been used, used in cranes and trolleybuses, or pieces of spiral heating elements (thermal electric heater), pieces of thick high-resistance wire. You can even reduce the current somewhat by using a stretched steel door spring. The ballast resistance can be switched on permanently (Fig. 14) or so that later it is relatively easy to select the desired current. Most high-power wirewound resistors are made in the form of an open spiral mounted on a ceramic frame up to half a meter long; as a rule, the wire from the heating elements is also wound into the spiral.
One end of such a resistance is connected to the CT output, and the end of the ground wire or electrode holder is equipped with a removable clamp, which can be easily thrown along the length of the resistance spiral, selecting the desired current (Fig. 15). The industry produces special resistance stores with switches and powerful rheostats for ST. The disadvantages of this method of adjustment include the bulkiness of the resistances, their strong heating during operation, and inconvenience when switching.
But ballast resistance, although often of a crude and primitive design, improves dynamic characteristic ST, moving it towards the steeply falling one. There are STs that operate extremely unsatisfactorily without ballast resistance.
In industrial devices, current regulation by switching on active resistance has not found widespread use due to their bulkiness and heating. But reactive shunting is very widely used - inclusion of a choke in the secondary circuit. Chokes have a variety of designs, often combined with the CT magnetic circuit into one whole, but they are made in such a way that their inductance, and therefore the reactance, is regulated mainly by the movement of parts of the magnetic circuit.
At the same time, the choke improves the arc burning process. Due to the design complexity, chokes are not used in the secondary circuit of homemade STs.
Adjusting the current in the secondary circuit of the CT is associated with certain problems. Thus, significant currents pass through the control device, which leads to its bulkiness. In addition, for the secondary circuit it is almost impossible to select such powerful standard switches that they can withstand a current of up to 200 A. Another thing is the circuit of the primary winding, where the currents are five times less, the switches for which are consumer goods. Active and reactive resistances can be connected in series with the primary winding. Only in this case, the resistance of the resistors and the inductance of the chokes should be significantly greater than in the secondary winding circuit.
Thus, a battery of several parallel-connected resistors PEV-50...100 with a total resistance of 6-8 Ohms can reduce the output current of 100 A by half. You can collect several batteries and install a switch. If you don’t have a powerful switch at your disposal, then you can get by with several.
By installing resistors according to the diagram (Fig. 16), you can achieve a combination of 0; 4; 6; 10 ohms. Instead of resistors, which will become very hot during operation, you can install a reactance inductor.
The inductor can be wound on the frame from a 200-300 W transformer, for example from a TV, by making taps every 40-60 turns connected to the switch (Fig. 17). You can turn off the power by turning on the secondary winding of some transformer (200-300 W) with a secondary winding rated at approximately 40 V as a choke. The choke can also be made on an open-ended - straight core.
This is convenient when you already have a ready-made coil with 200-400 turns of suitable wire. Then you need to stuff a package of straight transformer iron plates inside it. The required reactance is selected depending on the thickness of the package, guided by the welding current ST.
For example: a choke made from a coil containing supposedly about 400 turns of wire with a diameter of 1.4 mm, stuffed with an iron package with a total cross-section of 4.5 cm2, a length equal to the length of the coil, 14 cm. This made it possible to reduce the CT current to 120 A, t .e. approximately 2 times. A choke of this type can also be made with continuously variable reactance. It is necessary to make a structure to adjust the depth of insertion of the core rod into the cavity of the coil (Fig. 18, where 1 - core; 2 - latch; 3 - coil). A coil without a core has negligible resistance; with the core fully inserted, its resistance is maximum. A choke wound with a suitable wire does not heat up much, but its core vibrates strongly. This must be taken into account when screeding and fixing a set of iron plates.
It should be noted that for transformers with low currents x.x. (0.1...0.2 A) the above-described resistances in the primary winding circuit have virtually no effect on the output idle voltage. ST, and this does not affect the arc ignition process. For ST with x.x current. 1-2 A, when a ballast resistance is introduced into the primary circuit, the output voltage decreases noticeably. From my own experience, I can say that active and reactive resistance added in series to the primary winding do not have any pronounced negative effects on the ignition and burning of the arc.
Although the quality of the arc still deteriorates compared to the inclusion of a quenching resistor in the secondary winding circuit.
In CT you can also combine regulators or current limiters of different types. For example, you can use switching the turns of the primary winding in combination with connecting an additional resistor or in another way.
Reliability of welding transformer
The reliability of a welding machine depends both on design factors and on the mode and operating conditions. Reliable, carefully manufactured transformers operate for many years, easily withstanding short-term overloads and operational flaws. Lightweight portable structures, with wires covered in varnish, and even developing exorbitant power, as a rule, do not last long. They gradually wear out in the same way that, for example, clothes or shoes wear out over time. Although, given the significant volumes of work performed and the low costs of their production, this fully justifies their existence.
The worst enemies of ST are overheating and moisture penetration. The most effective remedy against overheating is reliable winding wires with a current density of no more than 5-7 A/mm2. In order for the wire to cool quickly, it must have good contact with air. To do this, slots are made in the windings (Fig. 19).
First, the first layer is wound and wooden or getinax strips 5-10 mm thick are inserted from the outer sides, then the strips are inserted every two layers of wire: so each layer has contact with air on one side. If the CT is installed without blowing, then the slots should be oriented vertically. Then air will constantly circulate through them: warm air rises up, and cold air is sucked in from below. It’s even better if the CT is constantly blown by a fan. In general, forced airflow has little effect on the heating rate of the transformer, but it noticeably speeds up its cooling.
Toroidal transformers heat up the fastest and coolest the worst. For a very hot CT, even powerful airflow will not solve this problem, and here you will have to maintain the temperature of the windings with a moderate operating mode. The cooling capacity of the transformer is also affected by the number of turns of the windings: the fewer turns, the higher it is.
In addition to the objective and understandable reasons for the failure of welding transformers, mainly related to imperfect design, based on my experience, I would like to point out another, seemingly implicit, but nevertheless very common way: how to ruin a ST.
The reason in this case, oddly enough, is the voltage drop in the electrical network... The CT stops welding normally if the mains voltage drops significantly or the power line has a significant internal resistance of the order of several ohms. Unfortunately, both the first and second are widespread in our country.
If, when the voltage drops, you can at least find out exactly the cause by taking a voltmeter and measuring the voltage, then in the second case the situation is more complicated: a high-resistance voltmeter does not sense a line resistance of several ohms and shows a normal voltage, but these few ohms can easily extinguish half the power of the CT, its own the resistance of which in arc mode is negligible. But what does the drop in power have to do with the “combustion” of the ST? Here's the thing. When the owner of a “welding”, having suffered quite a lot with a machine that doesn’t work from the 220 V network, realizes that he can’t change anything, but he’s working hard: earnings are lost or construction is underway, the solution gets cold... then in such cases very often The device is connected to a 380 V network.
The fact is that all wiring is usually done from a three-phase line: “zero” and three “phases”. If you connect to “zero” and one “phase” - phase voltage, then this is the usual 220 V. If you connect to “phase” and “phase” - linear voltage, then 380 V will be removed from two wires. And this is exactly how done by careless welders with single-phase machines designed for 220 V.
At the same time, the ST begins to work perfectly, although very often for a very short time. “They fire” because they are weak homemade designs, and reliable industrial devices. But everything is very simple: if the voltage in the general electrical network drops, for example, by 50 V, and the device does not want to work from 170 V, then between the “phases” nevertheless 330 V remains, which is fatal for any ST...
Often, owners of welding machines are simply too lazy to reschedule their “welds”: after all, the mass is considerable, and they remain on the street, get wet in the rain, are covered with snow... After such an attitude, an interturn short circuit is quite common, the CT windings “burn out”, and the entire structure fails.
But still, the main enemy of ST is overheating. Well, if you have to weld a lot and quickly, and the CT is wound with not so much wires and heats up catastrophically quickly,... you can suggest one cardinal remedy to combat overheating.
There is no need to worry about overheating if the entire transformer is completely immersed in transformer oil. Possessing significant thermal conductivity, oil not only removes heat from the windings, but also acts as an additional insulator. In its simplest form, this is a bucket of oil with a recessed CT, from which only four wires come out; such a “miracle” can sometimes be seen in yards in rural areas. Some transformer oil can be drained, for example, from old refrigeration units. Although people say that in case of emergency, other types are also suitable, including sunflower... I don’t know about sunflower, I haven’t checked it myself.
Another important element of the CT design is the outer casing. When installing a CT into a housing, special attention must be paid to its material and the possibility of air flow for cooling, while the top must be closed, protecting the transformer from rain. It is better to make housings or at least some of their parts from non-material. magnetic materials(brass, duralumin, getinaks, plastics). CT creates a powerful magnetic field, which attracts steel elements to it. If the housing is made of tin or steel panels are screwed opposite the axis of the primary winding, then during operation this entire structure will be pulled inward and vibrate. The sound is sometimes such that it can only be compared to the operation of a powerful circular saw. Therefore, the CT can be installed either in a solidly curved rigid steel case, which is not so susceptible to vibration, or panels can be made opposite at least the primary winding from non-magnetic materials.
You can install a fan in the housing or make it sealed and fill it with transformer oil.
And finally, the last recommendation. If you have nevertheless manufactured a CT, but are new to welding, then it is better to invite a specialist to test it. Welding is a very difficult task, and a person without experience is unlikely to succeed right away. Be sure to purchase or make a mask with glass number C-4 or E2. An electric arc emits powerful ultraviolet radiation, which negatively affects the skin and primarily the eyes. When the eyes are affected, a yellow spot appears in the field of vision, which then gradually disappears; they say “catch a bunny”.
If you manage to “catch” two such “bunnies” in a row at once, then immediately stop all experiments with electric arc. When several “bunnies” appear before your eyes, they, as a rule, then disappear and the person calms down, but later, after a few hours, this phenomenon is fraught with consequences that it is better not to experience on yourself.
A welding machine is a fairly popular device among both professionals and home craftsmen. But for domestic use, sometimes it makes no sense to buy an expensive unit, since it will be used in rare cases, for example, if you need to weld a pipe or install a fence. Therefore, it would be wiser to make a welding machine with your own hands, investing a minimal amount of money in it.
The main part of any welder working on the principle of electric arc welding is a transformer. This part can be removed from an old, unnecessary household appliances and make a homemade welding machine out of it. But in most cases, the transformer requires minor modifications. There are several ways to make a welder, which can be either the simplest or more complex, requiring knowledge in radio electronics.
To make a mini welding machine, you will need a couple of transformers removed from an unnecessary microwave oven. It’s easy to find a microwave from friends, acquaintances, neighbors, etc. The main thing is that it has a power in the range of 650-800 W, and it has a working transformer. If the stove has a more powerful transformer, then the device will have higher current ratings.
So, the transformer removed from the microwave has 2 windings: primary (primary) and secondary (secondary).
Secondary has more turns and a smaller wire cross-section. Therefore, in order for the transformer to become suitable for welding, it must be removed and replaced with a conductor with a larger cross-sectional area. To remove this winding from the transformer, it must be cut off on both sides of the part using a hacksaw.
This must be done with special care so as not to accidentally touch the primary winding with the saw.
When the coil is cut down, its remains will need to be removed from the magnetic circuit. This task will be much easier if you drill through the windings to relieve metal stress.
Do the same operations with the other transformer. As a result, you will get 2 parts with a primary winding of 220 V.
Important! Don't forget to remove the current shunts (shown by arrows in the photo below). This will increase the power of the device by 30 percent.
To make a secondary one, you will need to purchase 11-12 meters of wire. It must be multi-core and have cross section of at least 6 squares.
To make a welding machine, you will need to wind 18 turns (6 rows high and 3 layers thick) for each transformer.
You can wind both transformers with one wire or separately. In the second case, the coils should connect in series.
The winding should be done very tightly so that the wires do not dangle. Next, the primary windings need connect in parallel.
To connect the parts together, they can be screwed to a small piece of wood.
If you measure the voltage on the secondary of the transformer, then in this case it will be equal to 31-32 V.
This homemade welder can easily weld metal 2 mm thick with electrodes with a diameter of 2.5 mm.
It should be remembered that you should cook with such a homemade apparatus with rest breaks, since its windings become very hot. On average, after each electrode is used, the device should cool down for 20-30 minutes.
It will not be possible to cook thin metal with a unit made from a microwave, as it will cut it. To regulate the current, you can connect a ballast resistor or choke to the welder. The role of a resistor can be played by a segment steel wire of a certain length (selected experimentally), which is connected to the low-voltage winding.
AC welder
This is the most common type of metal welding machine. It is easy to make at home and is easy to use. But main drawback apparatus is large mass of step-down transformer, which is the basis of the unit.
For home use it is enough that the device produces a voltage of 60 V and can provide a current of 120-160 A. Therefore for primary, to which a 220 V household network is connected, you will need a wire with a cross-section from 3 mm 2 to 4 mm 2. But ideal option- this is a conductor with a cross section of 7 mm 2. With such a cross-section, voltage drops and possible additional loads will not be a problem for the device. It follows from this that the secondary requires a conductor 3 mm in diameter. If we take an aluminum conductor, then the calculated cross-section of the copper conductor is multiplied by a factor of 1.6. For secondary you will need a copper busbar with a cross-section of at least 25 mm 2
It is very important that the winding conductor is covered with rag insulation, since traditional PVC sheathing melts when heated, which can cause an inter-turn short circuit.
If you do not find a wire with the required cross-section, then you can make it yourself from several thinner conductors. But this will significantly increase the thickness of the wire and, accordingly, the dimensions of the unit.
First of all, the base of the transformer is manufactured - the core. It is made from metal plates(transformer steel). These plates should have a thickness of 0.35-0.55 mm. The pins connecting the plates must be well insulated from them. Before assembling the core, its dimensions are calculated, that is, the dimensions of the “window” and the cross-sectional area of the core, the so-called “core”. To calculate the area, use the formula: S cm 2 = a x b (see figure below).
But from practice it is known that if you make a core with an area of less than 30 cm 2, then it will be difficult to obtain a high-quality seam with such a device due to a lack of power reserve. Yes, and it will heat up very quickly. Therefore, the cross-section of the core must be at least 50 cm 2. Despite the fact that the weight of the unit will increase, it will become more reliable.
To assemble the core it is better to use L-shaped plates and place them as shown in the following figure until the thickness of the part reaches the required value.
Upon completion of assembly, the plates must be fastened together (at the corners) with bolts, then cleaned with a file and insulated with fabric insulation.
Now we can start winding the transformer.
One nuance should be taken into account: the ratio of turns on the core should be 40% to 60%. This means that on the side where the primary is located there should be a smaller number of secondary turns. Due to this, when welding begins, the winding with more turns will be partially switched off due to the occurrence of eddy currents. This will increase the current strength, which will have a positive effect on the quality of the seam.
When the winding of the transformer is completed, the network cable is connected to the common wire and to the 215 turn branch. Welding cables are connected to the secondary winding. After this, the resistance welding machine is ready for use.
DC device
To cook cast iron or stainless steel, you need an apparatus DC. It can be made from a conventional transformer unit, if its secondary winding connect the rectifier. Below is a diagram of a welding machine with a diode bridge.
Diagram of a welding machine with a diode bridge
The rectifier is assembled using D161 diodes capable of withstanding 200A. They must be installed on radiators. Also, to equalize the current ripple, you will need 2 capacitors (C1 and C2) of 50 V and 1500 μF. This electrical circuit also has a current regulator, the role of which is played by inductor L1. Welding cables are connected to contacts X5 and X4 (straight or reverse polarity), depending on the thickness of the metal being connected.
Inverter from computer power supply
It is impossible to make a welding machine from a computer power supply. But using its case and some parts, as well as the fan, is quite possible. So, if you make an inverter with your own hands, you can easily place it in the power supply case from the computer. All transistors (IRG4PC50U) and diodes (KD2997A) must be installed on radiators without using gaskets. For cooling parts it is desirable use a powerful fan, such as Thermaltake A2016. Despite their small sizes(80 x 80 mm), the cooler is capable of 4800 rpm. The fan also has a built-in speed controller. The latter are regulated using a thermocouple, which must be mounted on a radiator with installed diodes.
Advice! It is recommended to drill several additional holes in the power supply housing for better ventilation and heat dissipation. The overheat protection installed on the transistor radiators is set to operate at a temperature of 70-72 degrees.
Below is the principle electrical diagram welding inverter (in high resolution), which can be used to make a device that fits in the power supply housing.
The following photos show what components a homemade inverter welding machine consists of, and what it looks like after assembly.
Electric motor welder
To make a simple welding machine from an electric motor stator, you need to select the motor itself that meets certain requirements, namely, that its power be from 7 to 15 kW.
Advice! It is best to use a 2A series motor because it will have a large flux window.
You can get the required stator in places where scrap metal is accepted. As a rule, it will be cleared of wires and after a couple of blows with a sledgehammer it will split. But if the case is made of aluminum, then in order to remove the magnetic core from it, you will need to anneal the stator.
Preparing for work
Place the stator with the hole facing up and place bricks under the part. Next, put the wood inside and set it on fire. After a couple of hours of frying, the magnetic circuit will easily separate from the body. If there are wires in the housing, they can also be removed from the grooves after heat treatment. As a result, you will receive a magnetic circuit cleared of unnecessary elements.
This blank should be well impregnate with oil varnish and let it dry. To speed up the process, you can use a heat gun. Impregnation with varnish is done so that after removing the ties the bag does not crumble.
When the blank is completely dry, using a grinder, remove the zip ties, located on it. If the ties are not removed, they will act as short-circuited turns and take power from the transformer and also cause it to heat up.
After cleaning the magnetic circuit from unnecessary parts, you will need to make two end plates(see picture below).
The material for their manufacture can be either cardboard or pressboard. You also need to make two sleeves from these materials. One will be internal, and the second will be external. Next, you need:
- install both end plates on the blank;
- then insert (put on) the cylinders;
- wrap this entire structure with keeper or glass tape;
- saturate the resulting part with varnish and dry.
Transformer manufacturing
After carrying out the above steps, it will be possible to make a welding transformer from the magnetic core. For these purposes, you will need a wire covered with fabric or glass enamel insulation. To wind the primary winding, you will need a wire with a diameter of 2-2.5 mm. The secondary winding will require about 60 meters of copper busbar (8 x 4 mm).
So, the calculations are done as follows.
- 20 turns of wire with a diameter of at least 1.5 mm should be wound around the core, after which a voltage of 12 V should be applied to it.
- Measure the current flowing in this winding. The value should be about 2 A. If the value obtained is greater than the required one, then the number of turns should be increased, if the value is less than 2 A, then reduced.
- Count the number of turns obtained and divide it by 12. As a result, you will get a value that indicates how many turns are needed per 1 V of voltage.
For primary winding A conductor with a diameter of 2.36 mm is suitable, which needs to be folded in half. In principle, you can take any wire with a diameter of 1.5-2.5 mm. But first you need to calculate the cross-section of the conductors in the turn. First you need to wind the primary winding (at 220 V), and then the secondary. Its wire must be insulated along its entire length.
If you make a tap in the secondary winding in the area where 13 V is obtained and install a diode bridge, then this transformer can be used instead of a battery if you need to start the car. For welding, the voltage on the secondary winding should be in the range of 60-70 V, which will allow the use of electrodes with a diameter of 3 to 5 mm.
If you have laid both windings, and in this design there is only free space, then you can add 4 turns of copper busbar (40 x 5 mm). In this case, you will receive a spot welding winding that will allow you to join sheet metal up to 1.5 mm thick.
For case manufacturing It is not recommended to use metal. It is better to make it from PCB or plastic. In the places where the coil is attached to the body, rubber gaskets must be laid to reduce vibration and better insulate from conductive materials.
Homemade spot welding machine
The finished spot welding machine has enough high price, which does not justify its internal “stuffing”. It is designed very simply, and making it yourself will not be difficult.
To make your own spot welding machine, you will need one transformer from a microwave oven with a power of 700-800 W. You need to remove the secondary winding from it in the manner described above in the section where the manufacture of a welding machine from a microwave was discussed.
A spot welding machine is made in the following way.
- Make 2-3 turns inside the manipulator with a cable with a conductor diameter of at least 1 cm. This will be the secondary winding, allowing you to obtain a current of 1000 A.
- It is recommended to install copper lugs at the ends of the cable.
- If we connect 220 V to the primary winding, then on the secondary winding we will get a voltage of 2 V with a current of about 800 A. This will be enough to melt an ordinary nail in a few seconds.
- Next comes make a housing for the device. A wooden board is suitable for the base, from which several elements should be made, as shown in the following figure. The dimensions of all parts can be arbitrary and depend on the dimensions of the transformer.
- To give the case a more aesthetic appearance, sharp corners can be removed using hand router with an edge molding cutter installed on it.
- On one part of the welding jaws it is necessary cut a small wedge. Thanks to it, the ticks will be able to rise higher.
- Cut to back wall housing holes for the switch and network cable.
- When all the parts are ready and sanded, they can be painted with black paint or varnished.
- You will need to disconnect the power cable and limit switch from the unnecessary microwave. You will also need a metal door handle.
- If you don’t have a switch and a copper rod lying around at home, as well as copper clamps, then these parts must be purchased.
- Cut 2 small rods from the copper wire, which will serve as electrodes, and secure them in the clamps.
- Screw the switch to the back wall of the device.
- Screw the back wall and 2 posts to the base, as shown in the following photos.
- Attach the transformer to the base.
- Next, one network wire is connected to the primary winding of the transformer. The second power wire is connected to the first terminal of the switch. Then you need to attach the wire to the second terminal of the switch and connect it to the other terminal of the primary. But a break should be made on this wire and installed in it breaker removed from microwave. It will act as a welding start button. These wires must be long enough to accommodate the breaker at the end of the clamp.
- Attach the cover of the device with the installed handle to the stands and back wall.
- Secure the side walls of the housing.
- Now you can install the welding gun. First, drill holes at their ends into which the screws will be screwed.
- Next, attach a switch to the end.
- Insert the pliers into the body, first placing a square block between them for alignment. Drill holes through the side walls of the pliers and insert long nails into them to serve as axles.
- Attach copper electrodes to the ends of the pliers and align them so that the ends of the rods are opposite each other.
- To make the top electrode rise automatically, screw in 2 screws and attach an elastic band to them, as shown in the following photos.
- Turn on the unit, connect the electrodes and press the start button. You should see an electrical discharge between the copper rods.
- To check the operation of the unit, you can take metal washers and weld them.
In this case, the result was positive. Therefore, the creation of a spot welding machine can be considered complete.
Do-it-yourself welding in this case does not mean welding technology, but homemade equipment for electric welding. Working skills are acquired through industrial practice. Of course, before going to the workshop, you need to master the theoretical course. But you can put it into practice only if you have something to work with. This is the first argument in favor of, when mastering welding on your own, first taking care of the availability of appropriate equipment.
Second, a purchased welding machine is expensive. Rent is also not cheap, because... the probability of its failure due to unskilled use is high. Finally, in the outback, getting to the nearest point where you can rent a welder can be simply long and difficult. All in all, It is better to start your first steps in metal welding by making a welding installation with your own hands. And then - let it sit in a barn or garage until the opportunity arises. It’s never too late to spend money on branded welding if things work out.
What are we going to talk about?
This article discusses how to make equipment at home for:
- Electric arc welding with alternating current of industrial frequency 50/60 Hz and direct current up to 200 A. This is enough to weld metal structures up to approximately a corrugated fence on a frame made of corrugated pipe or a welded garage.
- Micro-arc welding of twisted wires is very simple and useful when laying or repairing electrical wiring.
- Spot pulse resistance welding - can be very useful when assembling products from thin steel sheets.
What we won't talk about
First, let's skip gas welding. The equipment for it costs pennies compared to consumables, you can’t make gas cylinders at home, and a homemade gas generator is a serious risk to life, plus carbide is expensive now, where it is still on sale.
The second is inverter electric arc welding. Indeed, a semi-automatic inverter welding allows a novice amateur to weld quite important structures. It is light and compact and can be carried by hand. But purchasing at retail the components of an inverter that allows for consistent high-quality welding will cost more than a finished machine. And an experienced welder will try to work with simplified homemade products, and refuse - “Give me a normal machine!” Plus, or rather minus, is that in order to make a more or less decent welding inverter, you need to have fairly solid experience and knowledge in electrical engineering and electronics.
The third is argon-arc welding. With whose light hand the claim that it is a hybrid of gas and arc has gone for a walk in RuNet, unknown. In fact, this is a type of arc welding: the inert gas argon does not participate in the welding process, but creates working area a cocoon that insulates it from the air. As a result, the welding seam is chemically pure, free from impurities of metal compounds with oxygen and nitrogen. Therefore, non-ferrous metals can be cooked under argon, incl. heterogeneous. In addition, it is possible to reduce the welding current and arc temperature without compromising its stability and weld with a non-consumable electrode.
It is quite possible to make equipment for argon-arc welding at home, but gas is very expensive. It is unlikely that you will need to cook aluminum, stainless steel or bronze as part of routine economic activities. And if you really need it, it’s easier to rent argon welding - compared to how much (in money) gas will go back into the atmosphere, it’s pennies.
Transformer
The basis of all “our” types of welding is a welding transformer. The procedure for its calculation and design features differ significantly from those of power supply (power) and signal (sound) transformers. The welding transformer operates in intermittent mode. If you design it for maximum current like continuous transformers, it will turn out to be prohibitively large, heavy and expensive. Ignorance of the features of electrical transformers for arc welding is the main reason for the failures of amateur designers. Therefore, let’s take a walk through welding transformers in the following order:
- a little theory - on the fingers, without formulas and brilliance;
- features of magnetic cores of welding transformers with recommendations for choosing from random ones;
- testing of available used equipment;
- calculation of a transformer for a welding machine;
- preparation of components and winding of windings;
- trial assembly and fine-tuning;
- commissioning.
Theory
An electrical transformer can be likened to a water supply storage tank. This is a rather deep analogy: a transformer operates due to the reserve of magnetic field energy in its magnetic circuit (core), which can be many times greater than that instantly transmitted from the power supply network to the consumer. And the formal description of losses due to eddy currents in steel is similar to that for water losses due to infiltration. Electricity losses in copper windings are formally similar to pressure losses in pipes due to viscous friction in the liquid.
Note: the difference is in losses due to evaporation and, accordingly, magnetic field scattering. The latter in the transformer are partially reversible, but smooth out the peaks of energy consumption in the secondary circuit.
An important factor in our case is the external current-voltage characteristic (VVC) of the transformer, or simply its external characteristic (VC) - the dependence of the voltage on the secondary winding (secondary) on the load current, with a constant voltage on the primary winding (primary). For power transformers, the VX is rigid (curve 1 in the figure); they are like a shallow, vast pool. If it is properly insulated and covered with a roof, then water losses are minimal and the pressure is quite stable, no matter how consumers turn the taps. But if there is gurgling in the drain - sushi oars, the water is drained. In relation to transformers, the power source must keep the output voltage as stable as possible to a certain threshold less than the maximum instantaneous power consumption, be economical, small and light. To do this:
- The steel grade for the core is selected with a more rectangular hysteresis loop.
- Design measures (core configuration, calculation method, configuration and arrangement of windings) reduce dissipation losses, losses in steel and copper in every possible way.
- The magnetic field induction in the core is taken less than the maximum permissible current form for transmission, because its distortion reduces efficiency.
Note: transformer steel with “angular” hysteresis is often called magnetically hard. This is not true. Magnetically hard materials retain strong residual magnetization; they are made by permanent magnets. And any transformer iron is soft magnetic.
You cannot cook from a transformer with a hard VX: the seam is torn, burned, and the metal splatters. The arc is inelastic: I moved the electrode slightly wrong and it goes out. Therefore, the welding transformer is made to look like a regular water tank. Its CV is soft (normal dissipation, curve 2): as the load current increases, the secondary voltage gradually drops. The normal scattering curve is approximated by a straight line incident at an angle of 45 degrees. This allows, due to a decrease in efficiency, to briefly extract several times more power from the same hardware, or resp. reduce the weight, size and cost of the transformer. In this case, the induction in the core can reach a saturation value, and for a short time even exceed it: the transformer will not go into a short circuit with zero power transfer, like a “silovik”, but will begin to heat up. Quite long: the thermal time constant of welding transformers is 20-40 minutes. If you then let it cool down and there is no unacceptable overheating, you can continue working. The relative drop in the secondary voltage ΔU2 (corresponding to the range of the arrows in the figure) of normal dissipation gradually increases with increasing range of fluctuations of the welding current Iw, which makes it easy to hold the arc during any type of work. The following properties are provided:
- The steel of the magnetic circuit is taken with hysteresis, more “oval”.
- Reversible scattering losses are normalized. By analogy: the pressure has dropped - consumers will not pour out much and quickly. And the water utility operator will have time to turn on the pumping.
- The induction is chosen close to the overheating limit; this allows, by reducing cosφ (a parameter equivalent to efficiency) at a current significantly different from the sinusoidal one, to take more power from the same steel.
Note: reversible scattering loss means that part of the power lines penetrates the secondary through the air, bypassing the magnetic circuit. The name is not entirely apt, just like “useful scattering”, because “reversible” losses for the efficiency of a transformer are no more useful than irreversible ones, but they soften the I/O.
As you can see, the conditions are completely different. So, should you definitely look for iron from a welder? Optional, for currents up to 200 A and peak power up to 7 kVA, but this is enough for the farm. Using design and design measures, as well as with the help of simple additional devices (see below), we will obtain on any hardware a VX curve 2a that is somewhat more rigid than normal. The efficiency of welding energy consumption is unlikely to exceed 60%, but for occasional work this is not a problem. But on delicate work and low currents, holding the arc and welding current will not be difficult, without much experience (ΔU2.2 and Iw1), at high currents Iw2 we will get acceptable weld quality, and it will be possible to cut metal up to 3-4 mm.
There are also welding transformers with a steeply falling VX, curve 3. This is more like a booster pump: either the output flow is at nominal level, regardless of the feed height, or there is none at all. They are even more compact and lightweight, but in order to withstand the welding mode at a steeply falling VX, it is necessary to respond to fluctuations ΔU2.1 of the order of a volt within a time of about 1 ms. Electronics can do this, so transformers with “steep” VX are often used in semi-automatic welding machines. If you cook from such a transformer manually, then the seam will be sluggish, undercooked, the arc will again be inelastic, and when you try to light it again, the electrode will stick every now and then.
Magnetic cores
The types of magnetic cores suitable for the manufacture of welding transformers are shown in Fig. Their names begin with the letter combination respectively. standard size. L means tape. For a welding transformer L or without L, there is no significant difference. If the prefix contains M (SHLM, PLM, ShM, PM) - ignore without discussion. This is iron of reduced height, unsuitable for a welder despite all its other outstanding advantages.
After the letters of the nominal value there are numbers indicating a, b and h in Fig. For example, for W20x40x90, the cross-sectional dimensions of the core (central rod) are 20x40 mm (a*b), and the window height h is 90 mm. Core cross-sectional area Sc = a*b; window area Sok = c*h is needed for accurate calculation of transformers. We will not use it: for an accurate calculation, we need to know the dependence of losses in steel and copper on the value of induction in a core of a given standard size, and for them, the grade of steel. Where will we get it if we run it on random hardware? We will calculate using a simplified method (see below), and then finalize it during testing. It will take more work, but we will get welding that you can actually work on.
Note: if the iron is rusty on the surface, then nothing, the properties of the transformer will not suffer from this. But if there are spots of tarnish on it, this is a defect. Once upon a time, this transformer overheated very much and the magnetic properties of its iron were irreversibly deteriorated.
Another important parameter of the magnetic circuit is its mass, weight. Since the specific density of steel is constant, it determines the volume of the core, and, accordingly, the power that can be taken from it. Magnetic cores with the following weight are suitable for the manufacture of welding transformers:
- O, OL – from 10 kg.
- P, PL – from 12 kg.
- W, SHL – from 16 kg.
Why Sh and ShL are needed heavier is clear: they have an “extra” side rod with “shoulders”. OL may be lighter because it does not have corners that require excess iron, and the bends of the magnetic force lines are smoother and for some other reasons, which will be discussed later. section.
Oh OL
The cost of toroid transformers is high due to the complexity of their winding. Therefore, the use of toroidal cores is limited. A torus suitable for welding can, firstly, be removed from the LATR - a laboratory autotransformer. Laboratory, which means it should not be afraid of overloads, and the hardware of LATRs provides a VH close to normal. But…
LATR is a very useful thing, first of all. If the core is still alive, it is better to restore the LATR. Suddenly you don’t need it, you can sell it, and the proceeds will be enough for welding suitable for your needs. Therefore, “bare” LATR cores are difficult to find.
Secondly, LATRs with a power of up to 500 VA are weak for welding. From the LATR-500 iron you can achieve welding with a 2.5 electrode in the mode: cook for 5 minutes - it cools down for 20 minutes, and we heat up. As in Arkady Raikin’s satire: mortar bar, brick yok. Brick bar, mortar yok. LATRs 750 and 1000 are very rare and useful.
Another torus suitable for all properties is the stator of an electric motor; Welding from it will turn out to be good enough for an exhibition. But it is no easier to find than LATR iron, and it is much more difficult to wind on it. In general, a welding transformer from an electric motor stator is a separate topic, there are so many complexities and nuances. First of all, with a thick wire wound around the donut. Having no experience in winding toroidal transformers, the probability of damaging an expensive wire and not getting welded is close to 100%. Therefore, alas, we will have to wait a little longer with the cooking apparatus on a triode transformer.
Sh, ShL
Armor cores are structurally designed for minimal dissipation, and it is almost impossible to standardize it. Welding on a regular Sh or ShL will turn out to be too tough. In addition, the cooling conditions for the windings on Ш and ШЛ are the worst. The only armored cores suitable for a welding transformer are those of increased height with spaced biscuits windings (see below), on the left in Fig. The windings are separated by dielectric non-magnetic heat-resistant and mechanically strong gaskets (see below) with a thickness of 1/6-1/8 of the core height.
For welding, the core Ш is welded (assembled from plates) necessarily across the roof, i.e. yoke-plate pairs are alternately oriented back and forth relative to each other. The method of normalizing dissipation by a non-magnetic gap is unsuitable for a welding transformer, because the losses are irreversible.
If you turn up a laminated Sh without a yoke, but with a cut in the plates between the core and the lintel (in the center), you are in luck. The plates of the signal transformers are laminated, and the steel on them, to reduce signal distortion, is used to initially give normal VX. But the likelihood of such luck is very small: signal transformers with kilowatt power are a rare curiosity.
Note: do not try to assemble a high Ш or ШЛ from a pair of ordinary ones, as on the right in Fig. A continuous straight gap, albeit a very thin one, means irreversible scattering and a steeply falling CV. Here, dissipation losses are almost similar to water losses due to evaporation.
PL, PLM
Rod cores are most suitable for welding. Of these, those laminated in pairs of identical L-shaped plates, see Fig., their irreversible scattering is the smallest. Secondly, the P and PL windings are wound in exactly the same halves, with half turns for each. The slightest magnetic or current asymmetry - the transformer hums, heats up, but there is no current. The third thing that may not seem obvious to those who have not forgotten the school gimlet rule is that the windings are wound onto the rods in one direction. Does something seem wrong? Does the magnetic flux in the core have to be closed? And you twist the gimlets according to the current, and not according to the turns. The directions of the currents in the half-windings are opposite, and magnetic fluxes are shown there. You can also check if the wiring protection is reliable: apply the network to 1 and 2’, and close 2 and 1’. If the machine does not immediately knock out, the transformer will howl and shake. However, who knows what's going on with your wiring. Better not.
Note: You can also find recommendations - to wind the windings of the welding P or PL on different rods. Like, VH is softening up. That’s how it is, but for this you need a special core, with rods of different sections (the secondary is smaller) and recesses that release power lines into the air in the right direction, see fig. right. Without this, we will get a noisy, shaking and gluttonous, but not cooking transformer.
If there is a transformer
A 6.3 A circuit breaker and an AC ammeter will also help determine the suitability of an old welder lying around God knows where and God knows how. You need either a non-contact induction ammeter (current clamp) or a 3 A pointer electromagnetic ammeter. A multimeter with alternating current limits will not lie, because the shape of the current in the circuit will be far from sinusoidal. Also, a long-neck liquid household thermometer, or, better yet, a digital multimeter with the ability to measure temperature and a probe for this. The step-by-step procedure for testing and preparing for further operation of an old welding transformer is as follows:
Calculation of a welding transformer
In RuNet you can find different methods for calculating welding transformers. Despite the apparent inconsistency, most of them are correct, but with full knowledge of the properties of steel and/or for a specific number of standard values of magnetic cores. The proposed methodology developed in Soviet times, when instead of choice there was a shortage of everything. For a transformer calculated using it, the VX drops a little steeply, somewhere between curves 2 and 3 in Fig. at the beginning. This is suitable for cutting, but for thinner work the transformer is supplemented with external devices (see below) that stretch the VX along the current axis to curve 2a.
The basis of calculation is usual: the arc burns stably under a voltage Ud of 18-24 V, and its ignition requires an instantaneous current 4-5 times greater than the rated welding current. Accordingly, the minimum open-circuit voltage Uхх of the secondary will be 55 V, but for cutting, since everything possible is squeezed out of the core, we take not the standard 60 V, but 75 V. Nothing more: it is unacceptable according to technical regulations, and the iron will not pull out. Another feature, for the same reasons, is the dynamic properties of the transformer, i.e. its ability to quickly transition from short-circuit mode (say, when short-circuited by drops of metal) to working mode is maintained without additional measures. True, such a transformer is prone to overheating, but since it is our own and in front of our eyes, and not in the far corner of a workshop or site, we will consider this acceptable. So:
- According to the formula from paragraph 2 previous. list we find the overall power;
- We find the maximum possible welding current Isv = Pg/Ud. 200 A is guaranteed if 3.6-4.8 kW can be removed from the iron. True, in the first case the arc will be sluggish, and it will be possible to cook only with a deuce or 2.5;
- We calculate the operating current of the primary at the maximum permissible network voltage for welding I1рmax = 1.1Pg(VA)/235 V. In fact, the norm for the network is 185-245 V, but for a homemade welder at the limit this is too much. We take 195-235 V;
- Based on the found value, we determine the tripping current of the circuit breaker as 1.2I1рmax;
- We assume the current density of the primary J1 = 5 A/sq. mm and, using I1рmax, we find the diameter of its copper wire d = (4S/3.1415)^0.5. Its total diameter with self-insulation is D = 0.25 + d, and if the wire is ready - tabular. To operate in the “brick bar, mortar yoke” mode, you can take J1 = 6-7 A/sq. mm, but only if the right wire no and not expected;
- We find the number of turns per volt of the primary: w = k2/Sс, where k2 = 50 for Sh and P, k2 = 40 for PL, ShL and k2 = 35 for O, OL;
- We find the total number of its turns W = 195k3w, where k3 = 1.03. k3 takes into account the energy loss of the winding due to leakage and in copper, which is formally expressed by the somewhat abstract parameter of the winding’s own voltage drop;
- We set the laying coefficient Kу = 0.8, add 3-5 mm to a and b of the magnetic circuit, calculate the number of layers of the winding, the average length of the turn and the footage of the wire
- We calculate the secondary similarly at J1 = 6 A/sq. mm, k3 = 1.05 and Ku = 0.85 for voltages of 50, 55, 60, 65, 70 and 75 V, in these places there will be taps for rough adjustment of the welding mode and compensation for fluctuations in the supply voltage.
Winding and finishing
The diameters of the wires in the calculation of windings are usually greater than 3 mm, and varnished winding wires with d>2.4 mm are rarely widely sold. In addition, the welder windings experience strong mechanical loads from electromagnetic forces, so finished wires are needed with an additional textile winding: PELSH, PELSHO, PB, PBD. They are even more difficult to find, and they are very expensive. The meterage of the wire for the welder is such that it is possible to insulate cheaper bare wires yourself. An additional advantage is that by twisting several stranded wires to the required S, we get a flexible wire, which is much easier to wind. Anyone who has tried to manually lay a tire of at least 10 square meters on a frame will appreciate it.
Isolation
Let's say there is a 2.5 sq.m. wire available. mm in PVC insulation, and for the secondary you need 20 m by 25 squares. We prepare 10 coils or coils of 25 m each. We unwind about 1 m of wire from each and remove the standard insulation, it is thick and not heat-resistant. We twist the exposed wires with a pair of pliers into an even, tight braid, and wrap it in order of increasing insulation cost:
- Using masking tape with an overlap of 75-80% turns, i.e. in 4-5 layers.
- Calico braid with an overlap of 2/3-3/4 turns, i.e. 3-4 layers.
- Cotton electrical tape with an overlap of 50-67%, in 2-3 layers.
Note: the wire for the secondary winding is prepared and wound after winding and testing the primary, see below.
Winding
A thin-walled homemade frame will not withstand the pressure of turns of thick wire, vibrations and jerks during operation. Therefore, the windings of welding transformers are made of frameless biscuits, and they are secured to the core with wedges made of textolite, fiberglass or, in extreme cases, bakelite plywood impregnated with liquid varnish (see above). The instructions for winding the windings of a welding transformer are as follows:
- We prepare a wooden boss with a height equal to the height of the winding and with dimensions in diameter 3-4 mm larger than a and b of the magnetic circuit;
- We nail or screw temporary plywood cheeks to it;
- We wrap the temporary frame in 3-4 layers of thin polyethylene film, covering the cheeks and wrapping them on the outside so that the wire does not stick to the wood;
- We wind the pre-insulated winding;
- Along the winding, we impregnate it twice with liquid varnish until it drips through;
- Once the impregnation has dried, carefully remove the cheeks, squeeze out the boss and peel off the film;
- We tightly tie the winding in 8-10 places evenly around the circumference with thin cord or propylene twine - it is ready for testing.
Finishing and finishing
We mix the core into a biscuit and tighten it with bolts, as expected. Winding tests are carried out in exactly the same way as tests of a questionable finished transformer, see above. It is better to use LATR; Iхх at an input voltage of 235 V should not exceed 0.45 A per 1 kVA of the overall power of the transformer. If it’s more, the primary is wound up. Winding wire connections are made with bolts (!), insulated with heat-shrinkable tube (HERE) in 2 layers or with cotton electrical tape in 4-5 layers.
Based on the test results, the number of turns of the secondary is adjusted. For example, the calculation gave 210 turns, but in reality Ixx fit into the norm at 216. Then we multiply the calculated turns of the secondary sections by 216/210 = 1.03 approx. Do not neglect decimal places, the quality of the transformer largely depends on them!
After finishing, we disassemble the core; We wrap the biscuit tightly with the same masking tape, calico or “rag” tape in 5-6, 4-5 or 2-3 layers, respectively. Wind across the turns, not along them! Now saturate it with liquid varnish again; when it dries - twice undiluted. This galette is ready, you can make a secondary one. When both are on the core, we test the transformer again now at Ixx (suddenly it curled somewhere), fix the biscuits and impregnate the entire transformer with normal varnish. Phew, the most dreary part of the work is over.
Pull VX
But he’s still too cool for us, haven’t you forgotten? Needs to be softened. The simplest way– a resistor in the secondary circuit is not suitable for us. Everything is very simple: at a resistance of only 0.1 Ohm at a current of 200, 4 kW of heat will be dissipated. If we have a welder with a capacity of 10 kVA or more, and we need to weld thin metal, we need a resistor. Whatever current is set by the regulator, its emissions when the arc is ignited are inevitable. Without active ballast, they will burn out the seam in places, and the resistor will extinguish them. But for us, weaklings, it will be of no use.
The reactive ballast (inductor, choke) will not take away excess power: it will absorb current surges, and then smoothly release them to the arc, this will stretch the VX as needed. But then you need a throttle with dispersion adjustment. And for it, the core is almost the same as that of a transformer, and the mechanics are quite complex, see fig.
We will go the other way: we will use active-reactive ballast, colloquially called gut by old welders, see fig. right. Material – steel wire rod 6 mm. The diameter of the turns is 15-20 cm. How many of them are shown in Fig. Apparently, for power up to 7 kVA this gut is correct. The air gaps between the turns are 4-6 cm. The active-reactive choke is connected to the transformer with an additional piece of welding cable (hose, simply), and the electrode holder is attached to it with a clothespin clamp. By selecting the connection point, it is possible, coupled with switching to secondary taps, to fine-tune the operating mode of the arc.
Note: An active-reactive choke can become red-hot during operation, so it requires a fireproof, heat-resistant, dielectric, non-magnetic lining. In theory, a special ceramic cradle. It is acceptable to replace it with a dry sand cushion, or formally with a violation, but not grossly, the welding gut is laid on bricks.
What about the rest?
This means, first of all, an electrode holder and a connecting device for the return hose (clamp, clothespin). Since our transformer is at its limit, we need to buy them ready-made, but those like those in Fig. right, no need. For a 400-600 A welding machine, the quality of contact in the holder is hardly noticeable, and it will also withstand simply winding up the return hose. And our homemade one, working with effort, can go haywire, seemingly for some unknown reason.
Next, the body of the device. It must be made of plywood; preferably bakelite impregnated, as described above. The bottom is 16 mm thick, the panel with the terminal block is 12 mm thick, and the walls and cover are 6 mm thick, so that they don’t come off during transportation. Why not sheet steel? It is ferromagnetic and in the stray field of a transformer can disrupt its operation, because we get everything we can out of him.
What's up terminal blocks, then the terminals themselves are made from M10 bolts. The base is the same textolite or fiberglass. Getinax, bakelite and carbolite are not suitable; pretty soon they will crumble, crack and delaminate.
Let's try a permanent one
Welding with direct current has a number of advantages, but the input voltage of any welding transformer becomes more severe at constant current. And ours, designed for the minimum possible power reserve, will become unacceptably stiff. The choke-intestine will no longer help here, even if it worked on direct current. In addition, it is necessary to protect expensive 200 A rectifier diodes from current and voltage surges. We need a reciprocal-absorbing infra-low frequency filter, FINCH. Although it looks reflective, you need to take into account the strong magnetic coupling between the halves of the coil.
The circuit of such a filter, known for many years, is shown in Fig. But immediately after its implementation by amateurs, it became clear that the operating voltage of capacitor C is low: voltage surges during arc ignition can reach 6-7 values of its Uхх, i.e. 450-500 V. Further, capacitors are needed that can withstand the circulation of high reactive power, only and only oil-paper ones (MBGCH, MBGO, KBG-MN). The following gives an idea of the weight and dimensions of single “cans” of these types (by the way, not cheap ones). Fig., and a battery will need 100-200 of them.
With a coil magnetic circuit it is simpler, although not entirely. Suitable for it are 2 PL power transformers TS-270 from old tube “coffin” TVs (data is in reference books and in RuNet), or similar ones, or SLs with similar or larger a, b, c and h. From 2 submarines, an SL is assembled with a gap, see figure, of 15-20 mm. It is fixed with textolite or plywood spacers. Winding – insulated wire from 20 sq. mm, how much will fit in the window; 16-20 turns. They wind it in 2 wires. The end of one is connected to the beginning of the other, this will be the middle point.
The filter is adjusted in an arc at the minimum and maximum values of Uхх. If the arc is sluggish at minimum, the electrode sticks, the gap is reduced. If the metal burns at maximum, increase it or, which will be more effective, cut off part of the side rods symmetrically. To prevent the core from crumbling, it is impregnated with liquid and then normal varnish. Finding the optimum inductance is quite difficult, but then welding works flawlessly on alternating current.
Microarc
The purpose of microarc welding is discussed at the beginning. The “equipment” for it is extremely simple: a step-down transformer 220/6.3 V 3-5 A. In tube times, radio amateurs connected to the filament winding of a standard power transformer. One electrode – the twisting of the wires itself (copper-aluminum, copper-steel is possible); the other is a graphite rod like a 2M pencil lead.
Nowadays, for micro-arc welding, they use more computer power supplies, or, for pulsed micro-arc welding, capacitor banks, see the video below. On direct current, the quality of work, of course, improves.
Video: homemade twist welding machine
Video: DIY welding machine from capacitors
Contact! There is contact!
Resistance welding in industry is mainly used in spot, seam and butt welding. At home, primarily in terms of energy consumption, pulsed point is feasible. It is suitable for welding and welding thin, from 0.1 to 3-4 mm, steel sheet parts. Arc welding will burn through a thin wall, and if the part is the size of a coin or less, then the softest arc will burn it entirely.
The principle of operation of resistance spot welding is illustrated in the figure: copper electrodes forcefully compress the parts, a current pulse in the steel-to-steel ohmic resistance zone heats the metal until electrodiffusion occurs; metal does not melt. The current needed for this is approx. 1000 A per 1 mm of thickness of the parts being welded. Yes, a current of 800 A will grab sheets of 1 and even 1.5 mm. But if this is not a craft for fun, but, say, a galvanized corrugated fence, then the first strong gust of wind will remind you: “Man, the current was rather weak!”
However, resistance spot welding is much more economical than arc welding: the no-load voltage of the welding transformer for it is 2 V. It consists of 2-contact steel-copper potential differences and the ohmic resistance of the penetration zone. The transformer for resistance welding is calculated in the same way as for arc welding, but the current density in the secondary winding is 30-50 or more A/sq. mm. The secondary of the contact-welding transformer contains 2-4 turns, is well cooled, and its utilization factor (the ratio of welding time to operating time at idling and cooling) many times lower.
There are many descriptions on the RuNet of homemade pulse-spot welders from unusable microwave ovens. They are, in general, correct, but repetition, as written in “1001 Nights,” is of no use. And old microwaves don’t lie in heaps in trash heaps. Therefore, we will deal with designs that are less known, but, by the way, more practical.
In Fig. – construction of a simple apparatus for pulsed spot welding. They can weld sheets up to 0.5 mm; It is perfect for small crafts, and magnetic cores of this and larger sizes are relatively affordable. Its advantage, in addition to its simplicity, is the clamping of the running rod of the welding pliers with a load. To work with a contact welding pulser, a third hand would not hurt, and if one has to forcefully squeeze the pliers, then it is generally inconvenient. Disadvantages – increased risk of accidents and injuries. If you accidentally give a pulse when the electrodes are brought together without the parts being welded, then the plasma will shoot out from the tongs, metal splashes will fly, the wiring protection will be knocked out, and the electrodes will fuse tightly.
The secondary winding is made of a 16x2 copper busbar. It can be assembled from strips of thin sheet copper (it will turn out flexible) or made from a piece of flattened refrigerant supply tube of a household air conditioner. The bus is isolated manually as described above.
Here in Fig. – drawings of a pulse spot welding machine are more powerful, for welding sheets up to 3 mm, and more reliable. Thanks to a fairly powerful return spring (from the armored mesh of the bed), accidental convergence of the pliers is excluded, and the eccentric clamp provides strong, stable compression of the pliers, on which the quality of the welded joint significantly depends. If something happens, the clamp can be instantly released with one blow on the eccentric lever. The disadvantage is the insulating pincer units, there are too many of them and they are complex. Another one is aluminum pincer rods. Firstly, they are not as strong as steel ones, and secondly, they are 2 unnecessary contact differences. Although the heat dissipation of aluminum is certainly excellent.
About electrodes
In amateur conditions, it is more advisable to insulate the electrodes at the installation site, as shown in Fig. right. There is no conveyor at home; you can always let the device cool down so that the insulating bushings do not overheat. This design will allow you to make rods from durable and cheap steel corrugated pipe, and also lengthen the wires (up to 2.5 m is permissible) and use a contact welding gun or external pliers, see fig. below.
In Fig. On the right you can see another feature of electrodes for resistance spot welding: a spherical contact surface (heel). Flat heels are more durable, so electrodes with them are widely used in industry. But the diameter of the flat heel of the electrode must be equal to 3 times the thickness of the adjacent material being welded, otherwise the weld spot will be burned either in the center (wide heel) or along the edges (narrow heel), and corrosion will occur from the welded joint even on stainless steel.
The last point about electrodes is their material and size. Red copper burns out quickly, so commercial electrodes for resistance welding are made of copper with a chromium additive. These should be used; at current copper prices it is more than justified. The diameter of the electrode is taken depending on the mode of its use, based on a current density of 100-200 A/sq. mm. According to heat transfer conditions, the length of the electrode is at least 3 of its diameters from the heel to the root (the beginning of the shank).
How to give impetus
In the simplest homemade pulse-contact welding machines, the current pulse is given manually: they simply turn on the welding transformer. This, of course, doesn’t do him any good, and the welding either lacks fusion or burns out. However, automating the supply and normalization of welding pulses is not so difficult.
A diagram of a simple but reliable welding pulse generator, proven by long practice, is shown in Fig. Auxiliary transformer T1 is a regular 25-40 W power transformer. The voltage of winding II is indicated by the backlight. You can replace it with 2 LEDs connected back-to-back with a quenching resistor (usual, 0.5 W) 120-150 Ohm, then the voltage II will be 6 V.
Voltage III - 12-15 V. 24 is possible, then capacitor C1 (regular electrolytic) is needed for a voltage of 40 V. Diodes V1-V4 and V5-V8 - any rectifier bridges for 1 and from 12 A, respectively. Thyristor V9 - 12 or more A 400 V. Optothyristors from computer power supplies or TO-12.5, TO-25 are suitable. Resistor R1 is a wire-wound resistor; it is used to regulate the pulse duration. Transformer T2 – welding.