I'm already tired of assembling low-frequency amplifiers on microcircuits, my hands are itching, and I wanted to solder something serious. I decided to solder a transistor amplifier with bipolar power supply. The power source will be a linear power supply with a toroidal transformer, the winding of which I will talk about in this article.
First we need to decide on the power of the amplifier, the number of channels and load resistance.
I will have two channels, the output power will be approximately 100W per channel, the load resistance will be 4 Ohms.
You don’t have to bother and take a 300W transformer, but this is extra size and weight. Fortunately, if a class AB amplifier has an efficiency of approximately 50%, then in order to get 100W at the output, you need to consume 200W. If two channels are 100W each, then the consumption will be 400W. This is all approximate, and with the condition that the input signal will be a sinusoid with a constant amplitude. I don’t think that among reasonable people there are fans of listening to terrible squeaking in speakers.
The music we listen to has a sine wave waveform that varies in both frequency and amplitude. This signal will not always have a maximum amplitude; at such moments the electrolytic capacitor of the power source will be charged, and discharged at maximum amplitudes, thereby saving on transformer power. Again, if you are not a fan of listening to squeaking in the speaker system.
Let's calculate the power and voltage of our future transformer. Download and run the program.
We fill in all the fields at the top of the program, set the quiescent current to 10mA, the preamplifier current to 0mA, select the purpose and type of signal according to the taste of the music you are listening to. Click “Apply”.
The program calculated the voltage idle speed power source, as well as capacitor capacity, these ratings are advisory in nature and are given for one arm.
Next, fill out the two lower windows in accordance with the recommended values and click “Calculate”. We got the output voltage of the transformer windings, I have 34.5V on each arm, the current of the secondary windings is 1.7A, diode parameters and connection diagram.
We have decided on the transformer parameters, now we download and run the program. We will calculate the winding data.
My core is toroidal and has dimensions of 130*80*25. Fill in the fields of the program.
We set the induction amplitude to 1.2 T, or maybe one and a half (as in my case), this is for strip cores, and for plate cores we set it to 1 T. This parameter depends on the hardware.
Current density for class AB is from 3.5-4 A/mm2, for class A 2.5 A/mm2.
We set the currents and voltage of the secondary windings, click calculate.
So, we got the number of turns of the primary and secondary windings, as well as the diameters of the wires.
You can do without calculations, wind approximately 900 turns, and periodically connect the winding to a 220V network in series through an incandescent lamp with a rated voltage of 220V.
If the lamp stays on, even at half heat, then we move on, checking periodically. As soon as the lamp stops glowing, it is necessary to measure the no-load current (but without the lamp, we connect the winding directly to the network), which should be 10-100 mA.
If the no-load current is less than 10mA, then this is not very good. Due to the high resistance, the transformer will heat up under the load. If the current exceeds 100mA, the transformer will heat up at idle. Although there are transformers with no-load current and 300mA, they heat up without load and hum terribly.
You can start winding the transformer itself. I need to wind 1291 turns of the primary winding with a wire whose diameter is 0.6 mm. Notice the diameter, not the cross-section! I have a 0.63mm wire.
I wrap it with rag tape. Once I wrapped the core with one lavsan tape, without electrical tape (or cardboard), and after winding several layers a breakdown occurred. Apparently the lower layers of the wire were crushed, and the varnish was damaged by the sharp edge of the core. Now, when winding toroidal transformers, I always wind the core with rag tape.
Mylar tape can be bought in the store, in the form of a baking sleeve, which is cut into ribbons using a razor blade and a metal ruler.
We take a 40cm wooden ruler, saw through both edges so that the wire can be wound around it. We wind a large amount of wire (I had to wind 1300 turns several times).
I wind all the windings clockwise, as in the picture.
We secure the free end of the wire with tape, or thread, and wind the winding layer turn to turn.
Solder the wires of the primary winding. We isolate the areas of soldering and stripping of varnish.
I'll give you one little advice. When soldering wires to the terminals of the primary winding, choose high-quality and durable wires, or do not solder them, but place them in dielectric tubes (heat shrink, cambric). While I was winding the secondary windings, my leads broke off due to repeated bending. I took the wires from the PC power supply.
We overlap 4-5 layers of mylar tape taken from the baking sleeve.
Don’t forget to write down the number of turns in each layer on a piece of paper so you don’t forget. After all, winding a transformer can last not 1-2 days, but a month or several months, when there is no time, and you can forget everything.
We wind the remaining layers of wire in the same direction, between which we place layers of lavsan tape insulation.
The connection points must be soldered and insulated with heat shrink tubing.
When you reel it in required quantity turns of the primary winding of a toroidal transformer, you need to connect the winding in series through a 220V lamp to the network, as mentioned above. The lamp should not glow. If it lights up, it means you have a small number of turns, or a short circuit between layers or turns (if the wire is bad).
My no-load current is 11mA.
Solder the tap. We isolate the primary winding from the secondary well, maybe 6-8 layers of Mylar tape.
The secondary winding can be wound according to the calculations made above, or using the following method.
We take a thin wire and wind two or three dozen turns over the “primary”. Next, we connect the primary winding to the network and measure the voltage on our experimental winding. I got 18 turns of 2.6V.
Dividing 2.6V into 18 turns, I calculated that one turn is equal to 0.144V. The more turns on the experimental winding are wound, the more accurate the calculation. Next, I take the voltage I need on one of the secondary windings (I have 35V) and divide by 0.144V, I get the number of turns of the secondary winding equal to 243.
Winding the “secondary” is no different. We wind it in the same direction, with the same shuttle, only we take the diameter of the wire from the calculations above. My wire diameter is 1.25mm (I didn’t have a smaller one).
Many amateur welders dream of a toroidal transformer. After all, it has long been known that the weight and size characteristics of toroids are much better than those of “W” and “U”-shaped transformers. So, with the same characteristics, the toroid is 1.3-1.5 times smaller. The reason why many do not undertake the manufacture of such a transformer is the lack of iron. This article will help you find a way out of this situation.
The design involves the manufacture of a toroidal transformer from used industrial welding transformer. To do this, it is disassembled, and a donut is assembled from plates measuring 90X450 mm. The required cross-sectional area of the core depends on the number of plates.
In principle, the plates can also be used from power transformers of old tube color TVs. Transformer TS270, TSA310 are being removed. The U-shaped cores are broken into plates with a hammer blow, which are straightened on an anvil.
To make a donut, you first need to rivet a hoop from plates with an outer diameter of 260 mm. Then the first plate is inserted inside the hoop, holding it with your hand so that it does not unwind, the second one is inserted end-to-end, and so on, until the internal diameter of the donut is 120 mm. If the donut is made from TC270 transformers, then the diameter must be recalculated to achieve the required cross-sectional area. You can make two bagels and put them together. In this case, the external and internal diameters of the donut can be left unchanged.
The edges of the toroid are processed with a file. From electrical cardboard we make two rings with an outer diameter of 270 mm, an inner diameter of 110 mm, and a strip 90 mm wide. We apply electric cardboard blanks to the donut and wrap them with electrical tape on a fabric basis, you can wrap them with tape from the demagnetization loops of picture tubes. The primary winding is wound with PEV-2 wire with a diameter of 2.0 mm, the number of turns for 220 V is approximately 170. This largely depends on the density of the assembly of the plates. Exact quantity coil can be verified experimentally. If the no-load current is more than 1-2 A, then it is necessary to rewind the turns; if it is less, rewind it. The secondary winding is wound with PV3 wire with a cross-section of 15-20 mm, 30 turns. The third winding also contains 30 turns, but wound with MGTF 0.35 wire. Tape insulation is laid between the windings.
After testing the transformer, you can begin manufacturing the control circuit. It is a phase current regulator. The alternating voltage taken from the third winding of the transformer is rectified by a bridge on diodes VD5-VD8. The positive half-wave charges capacitor C1 through resistors R1 and R2. When the voltage across it reaches approximately six volts, a breakdown of the analogue of the low-voltage dinistor, assembled on the zener diode VD6 and the thyristor VS3, occurs, and through the diode VD3, the thyristor VS1 opens. Capacity C1 is discharged. The same thing happens with a negative half-wave, only diode VD4 and thyristor VS2 open. Resistor R3 serves to limit the current through the dinistor analogue.
The setup consists of adjusting resistor R1 to the required welding current control zone.
As SA1, you can use any 25 A automatic machine KD209A can be replaced with KD202V-KD202M or any others with a current of more than 0.7 A and a voltage of more than 70 V. The KUKLA thyristor can be replaced with KU201-KU202. Resistors R1 and R2 - for a power of at least 10 W. C1 - K50-6. VD1, VD2, VS1, VS2 for a current of 160-250 A with any voltage group. They must be installed on radiators with a cooling area of at least 100 cm2.
Winding 3 of the transformer is designed for a voltage of 40 V, and the secondary, if necessary, can be increased.
They're standing welding inverters inexpensive, purchasing them today is not a problem. And yet, many home craftsmen are interested in the question of how to make a transformer (welding) with their own hands. How difficult is it and how will it work? homemade apparatus. In principle, it is not difficult to do it with the right approach. The main thing is the winding of the transformer, because the power of the unit and the quality of its work depend on the correctly selected number of turns and the cross-section of the wire used.
So, before winding the welding transformer, it is necessary to calculate it according to all the required parameters. It should be noted that the calculations carried out do not always correspond to standard rules and diagrams, because the welding machine is sometimes assembled from materials other than those used in factory assembly. That is, what they found, they used.
For example, not the best transformer iron or winding wire was used. But even after such winding, the transformers cook perfectly, although they hum and get very hot. Let us add that when choosing transformer iron, you need to pay attention to such an indicator as the shape of the core. It can be armored or rod. The second type is used in homemade welding transformers more often because they have a better efficiency. True, the labor intensity of winding a transformer with your own hands is much higher here. But this does not scare the masters.
Let us add that the transformer can be wound according to several schemes.
- A network winding is when both coils are equal in number of turns and they are connected in series.
- Both windings are connected according to the back-to-back principle.
- The wound wire is located on one side of the core.
- The same as in the previous position, only on two sides connected in series.
The most simple circuit– the last one. It is usually used to assemble a transformer at home. In it, the secondary winding consists of two equal halves. And they are located on opposite shoulders of the magnetic circuit. The connection, as mentioned above, is serial.
The calculation is based on theoretical parameters, on the basis of which the actual parameters of the magnetic circuit will have to be selected. The main welding parameter is the current supplied to the electrode. Since in everyday life electrodes with a diameter of 2; 3 or 4 mm, then a current of 120-130 amperes will be sufficient for them. Now you can correctly calculate the power of the welding transformer using this formula:
P=U x I x cos φ / η
U is the open circuit voltage, I is the current strength (120-130 A), cos φ is taken equal to 0.8, η is the efficiency factor, which for homemade welding machines is 0.7.
The calculated power value should be checked according to the table with the cross-section of the magnetic circuit. The table value for such parameters is usually 28 cm², but in fact it is necessary to choose from the range of 25-60 cm². Now, using other reference tables, the number of turns of wire relative to the cross-section of the core is selected.
Very important point– the larger the area of the core used for the transformer, the fewer turns there should be in the coil. The thing is that a large number of wound turns may not fit into the hole in the magnetic circuit. The calculation of the number of turns is made using this formula:
N = 4960 × U/(S × I), where U is the voltage of the power source on the primary winding, I is the current of the secondary winding, in fact, this is the same welding current, S – cross-sectional area of the core.
And the number of turns on the secondary winding can be calculated using the ratio:
U1/U2=N1/N2
The no-load voltage on the secondary winding in homemade welding transformers is 45-50 volts.
How to wind a transformer
So, the calculations have been carried out, the parameters of the elements of the step-up transformer used have been determined, the winding circuit has been determined, and you can proceed to the rewinding process itself. But before that, you need to deal with the wires that will be wound around the core.
A copper wire in glass cloth or cotton insulation is wound onto the primary winding. No rubber. Based on the current strength on the primary winding equal to 25 amperes, the cross-section of the winding wire is 5-6 mm². The cross-section of the wire on the secondary winding should be 30-35 mm², because a high current flows through it (120-130 A). Special attention The insulation of this wire must be heat resistant. Now everything is ready, you can proceed to winding the teroidal transformer.
Before rewinding a transformer, it is necessary to understand one truth that the primary winding wires are subject to greater stress because they use a smaller conductor. In addition, the density of the laid coils here is higher, so they heat up more. That is why special attention must be paid to the quality of installation in the primary winding.
It happens that homemade transformer It is assembled not from a single piece of wire, but from several pieces. There is nothing wrong with this, because the ends of the pieces can be joined. To do this, you cannot use twisting; it is better to connect the two ends with a copper wire in several turns, and then solder the joint and insulate it.
The coils must be wound carefully, pressing them tightly against each other. In this case, the wire should not be laid strictly perpendicular to the tangent of the iron, but slightly to the side. But internal winding should be ahead. This will simply make it easy to press the next wrap onto the previous one. There is no need to trim the wire.
Please note that during the process of rewinding the transformer, the wire is fed in an even state. Bends and bends will only complicate the process itself. Therefore, it is better to wrap the wire around your hand and tighten it during installation.
To wind a toroidal transformer, each laid layer must be insulated. To do this, it is better to use a special impregnated latto fabric, which, upon contact, sticks to everything. Or you can use construction tape that you wrap around the transformer yourself. It is most convenient if the tape is cut into strips 15 mm wide. They are easy to cover a layer of wire, and at the same time you need to try to make sure that inner part The windings were covered with insulating material in two layers, and on the outside in one.
After which the entire winding must be lubricated with PVA glue. Firstly, it will strengthen the insulation, making it monolithic. Secondly, the winding will not hum. You shouldn’t feel sorry for PVA; you need to treat the entire surface well with it. After which the device must be dried. And then wind another layer of turns and so on until the welding transformer is completely ready. Winding the toroidal transformer with your own hands is finished.
Rewinding a transformer, carried out correctly, is a guarantee high quality and its long-term operation. A rewinded device will work exactly the same as a practically new one. Of course, it buzzes more, but in all other respects it is still the same necessary device.
Winding materials
As a core, profile plates made of a special alloy are mainly used. They are collected according to required thickness, taking into account the design cross-section of the core. There are several shapes of plates, but W-shaped elements are most often used.
The transformer frame is, in principle, an insulator that protects the core from the windings. The reel also rests on it. The frame and dielectric material are made; it must be thin (0.5-2.0 mm) to fit into the core window. If an old transformer is rewound, then the functions of the frame can be performed by cardboard, textolite, and so on. The dimensions of the frame and its shape are determined by the parameters of the core. But the height of the structure should be more sizes windings
For toroidal transformers it is better to use copper wires, coated with protective enamel. For welding machines, it is better to use copper or aluminum wires with cellulose, cotton or fiberglass insulation. Last view not the best. It copes well with loads, especially with high temperatures, but during vibration the fibers delaminate, and this is a violation of the insulating layer. As for the output wires, it is optimal if they are of different colors. This will simplify the connection method.
As you can see, rewinding your own old transformer is not very difficult. This, of course, will take a lot of time, but the device will work well. In any case, it will be cheaper than buying a new one.
Winding a transformer with your own hands is a simple procedure in itself, but it requires significant preparatory work. Some people involved in the manufacture of various radio equipment or power tools have needs for transformers for specific needs. Since it is not always possible to purchase a specific transformer for specific cases, many wind them themselves. Those who make a transformer with their own hands for the first time often cannot solve problems related to the correct calculation, selection of all parts and winding technology. It is important to understand that assembling and winding a step-up transformer and a step-down transformer are not the same thing.
The winding of the toroidal device is also significantly different. Since most radio amateurs or craftsmen who need to create a transforming device for the needs of their power equipment do not always have the appropriate knowledge and skills on how to make a transforming device, therefore this material is aimed specifically at this category of people.
Preparing for winding
The first step is to correctly calculate the transformer. The load on the transformer must be calculated. It is calculated by summing all connected devices (motors, transmitters, etc.) that will be powered by the transformer. For example, a radio station has 3 channels with a power of 15, 10 and 15 watts. The total power will be 15+10+15 = 40 watts. Next, a correction is made for the efficiency of the circuit. So, most transmitters have an efficiency of about 70% (more accurate will be in the description of a specific circuit), so such an object should be powered not by 40 W, but by 40/0.7 = 57.15 W. It is worth noting that the transformer also has its own efficiency. Typically, the efficiency of a transformer is 95-97%, but you should make a correction for homemade products and accept an efficiency of 85-90% (selected independently). Thus, the required power increases: 57.15/0.9 = 63.5 W. Typically, transformers of this power weigh about 1.2-1.5 kg.
Next, the input and output voltages are determined. For example, let's take a step-down transformer with voltages of 220 V input and 12 V output, standard frequency (50 Hz). Determine the number of turns. So, on one winding their number is 220 * 0.73 = 161 turns (rounded up to a whole number), and on the bottom 12 * 0.73 = 9 turns.
After determining the number of turns, they begin to determine the diameter of the wire. To do this, you need to know the flowing current and current density. For installations up to 1 kW, the current density is chosen in the range of 1.5 - 3 A/mm 2, the current itself is approximately calculated based on the power. So, the maximum current for the selected example will be about 0.5-1.5 A. Since the transformer will operate with a maximum of 100W load with natural air cooled, then the current density is taken to be about 2 A/mm 2. Based on these data, we determine the wire cross-section 1/2 = 0.5 mm 2. In principle, the cross-section is sufficient to select a conductor, but sometimes the diameter is also required. Since the cross section is found using the formula pd 2 /2, the diameter is equal to the root of 2 * 0.5/3.14 = 0.56 mm.
In the same way, find the cross-section and diameter of the second winding (or, if there are more of them, then all the others).
Winding materials
Winding a transformer requires careful selection of the materials used. So, important have almost all the details. You will need:
- Transformer frame. It is necessary to isolate the core from the windings, and it also holds the winding coils. Its manufacture is carried out from a durable dielectric material, which must be quite thin so as not to occupy space in the intervals (“window”) of the core. Often, special cardboard, textolite, fibers, etc. are used for these purposes. It should have a thickness of at least 0.5 m and a maximum of 2 mm. The frame must be glued; for this, ordinary adhesives for carpentry work (nitro adhesives) are used. The shapes and dimensions of the frames are determined by the shapes and dimensions of the core. In this case, the height of the frame should be slightly greater than the height of the plates (winding height). To determine its dimensions, it is necessary to make preliminary measurements of the plates and estimate the approximate height of the winding.
- Core. A magnetic circuit is used as a core. Plates from a disassembled transformer are best suited for this, since they are made of special alloys and are already designed for a certain number of turns. The most common shape of a magnetic circuit resembles the letter “W”. Moreover, it can be cut from various blanks available. To determine the dimensions, you must first wind the wires of the windings. To the winding, which has greatest number turns determine the length and width of the core plates. To do this, take the length of the winding + 2-5 cm, and the width of the winding + 1-3 cm. In this way, an approximate determination of the dimensions of the core occurs.
- Wire. Here we consider the winding and wires for the terminals. Best choice for winding the coils of a transforming device, copper wires with enamel insulation (type “PEL” / “PE”) are considered; these wires are sufficient for winding not only transformers for amateur radio needs, but also for power transformers (for example, for welding). They have a wide selection of cross-sections, which allows you to purchase the wire of the desired cross-section. The wires that come out from the coils must have a larger cross-section and be insulated with PVC or rubber. Wires of the “PV” series with a cross section of 0.5 mm 2 are often used. It is recommended to use wires with insulation of different colors for the output (to avoid confusion when connecting).
- Insulating pads. They are necessary to increase the insulation of the winding wire. Typically, thick and thin paper is used as spacers (tracing paper works well), which is placed between the rows. In this case, the paper must be intact, without breaks or punctures. This paper is also used to wrap the windings after they are all ready.
Ways to speed up the process
Many radio amateurs often have special primitive devices for winding windings. Example: a primitive machine for winding windings is a table (often a stand) on which bars with a rotating longitudinal axis are installed. The length of the axis is selected 1.5-2 times greater than the length of the frame of the transforming device coils (taken maximum length), at one of the exits from the bars the axis must have a handle for rotation.
A reel frame is put on the axis, which is locked on both sides with restrictive pins (they prevent the frame from moving along the axis).
Next, a winding wire is attached to the coil at one end and winding is carried out by rotating the axis handle. Such a primitive design will significantly speed up the winding of windings and make it more accurate.
Winding process
Winding a transformer involves winding windings. To do this, the wire that is planned to be used for windings is wound tightly onto any coil (to simplify the process). Next, the coil itself is installed either on the device indicated above, or it is wound “manually” (this is difficult and inconvenient). After this, the end of the winding wire is fixed to the winding coil, to which the lead wire is soldered (this can be done either at the beginning or at the end of the operation). Next, the coil begins to rotate.
In this case, the coil should not move anywhere, and the wire should have strong tension for tight laying.
Winding the turns of wire longitudinally should be done so that the turns fit together as closely as possible. After the first row of turns has been wound lengthwise, it is wrapped with special insulating paper in several layers, after which the next row of turns is wound. In this case, the rows should fit tightly to each other.
During the winding process, you should control the number of turns and stop after winding the required number. It is important that full turns are counted, without taking into account the wire consumption (i.e. the second row of turns requires more wire, but the number of turns is wound).
Winding a transformer with your own hands is not a difficult task if you prepare for it in advance. People who make various radio equipment or power tools have a need for transformers for specific needs. Since it is not always possible to purchase certain products, craftsmen often wind toroidal transformers themselves. Those who try to wind the winding for the first time encounter difficulties: they cannot determine the correctness of the calculations or select the appropriate parts and technology. It is necessary to understand that different types are wound differently.
Also toroidal devices are radically different. The calculation of a toroidal transformer and its winding will be special. Since radio amateurs and craftsmen create parts for power equipment, but do not always have sufficient knowledge and experience to manufacture them, this material will help this category of people understand the nuances.
Preparing for winding
Required materials
Winding materials require careful selection, every detail is important. In particular, you will need:
- Transformer frame. It is used to insulate the core from the windings and also holds the winding coils. It is made from strong and thin dielectric materials so as not to take up too much space in the intervals (“windows”) of the core. You can use cardboard, microfiber, textolite. The thickness of the material should not be more than 2 mm. The frame is glued together using ordinary carpentry glue (nitro glue). Its shape and dimensions depend entirely on the core, its height is slightly greater than that of the plate (winding height).
- Core. This role is usually performed by magnetic circuits. The best solution will be the use of plates from disassembled transformers, since they are made from suitable alloys and are designed for a certain number of turns. Magnetic cores have a variety of shapes, but most often there are products in the shape of the letter “W”. In addition, they can be cut from various blanks that are available. To determine the exact dimensions, the wires of the windings are pre-wound.
- Wires. Here you need to use two types: for winding and for leads. Optimal solution for transforming devices - copper wires with enamel insulation (PEL or PE type). They are enough even for power transformers. A wide selection of sections allows you to choose the most suitable option. PV wires are also often used. For the output, it is best to take wires with multi-colored insulation so as not to get confused when connecting.
- Insulation pads. Helps increase the insulation of the winding wire. As a rule, thin and thick paper(tracing paper works great), which should be laid between the rows. But the paper must be intact, there should be no tears or punctures, even the most insignificant ones.
How to speed up your workflow
Many radio amateurs have in their arsenal simple special units, with the help of which the winding is made. In many cases, we are talking about simple structures in the form of a small table or table stand, on which several bars with a rotating longitudinal axis are installed. The length of the axis itself must exceed the length of the winding frame by 2 times. A handle is attached to one of the exits from the bars, allowing you to rotate the device.
Reel frames are placed on the axles, which are locked on both sides with limiting pins (they prevent the frame from moving along the axis).