The article describes how to build a three-phase (single-phase) 220/380 V generator based on an AC asynchronous electric motor. A three-phase asynchronous electric motor, invented at the end of the 19th century by the Russian electrical engineer M.O. Dolivo-Dobrovolsky, has now become predominantly widespread both in industry and in agriculture, as well as in everyday life.
Asynchronous electric motors are the simplest and most reliable to operate. Therefore, in all cases where this is permissible under the conditions of the electric drive and there is no need for reactive power compensation, asynchronous AC motors should be used.
There are two main types of asynchronous motors: with squirrel-cage rotor and with phase rotor. An asynchronous squirrel-cage electric motor consists of a stationary part - the stator and a moving part - the rotor, rotating in bearings mounted in two motor shields. The stator and rotor cores are made from separate electrical steel sheets insulated from one another. A winding made of insulated wire. A rod winding is placed in the grooves of the rotor core or molten aluminum is poured. Jumper rings short-circuit the rotor winding at the ends (hence the name short-circuited). Unlike a squirrel-cage rotor, a winding made like a stator winding is placed in the slots of a phase-wound rotor. The ends of the winding are brought to slip rings, mounted on a shaft. Brushes slide along the rings, connecting the winding to a starting or control rheostat.
Asynchronous electric motors with a wound rotor are more expensive devices, require qualified maintenance, are less reliable, and therefore are used only in those industries where they cannot be done without them. For this reason, they are not very common, and we will not consider them further.
A current flows through the stator winding connected to a three-phase circuit, creating a rotating magnetic field. The magnetic field lines of the rotating stator field cross the rotor winding bars and induce an electromotive force (EMF) in them. Under the influence of this EMF, current flows in the short-circuited rotor rods. Magnetic fluxes arise around the rods, creating a general magnetic field of the rotor, which, interacting with the rotating magnetic field of the stator, creates a force causing the rotor to rotate in the direction of rotation magnetic field stator.
The rotor rotation frequency is slightly less than the rotation frequency of the magnetic field created by the stator winding. This indicator is characterized by slip S and is for most engines in the range from 2 to 10%.
Most commonly used in industrial installations three-phase asynchronous electric motors, which are produced in the form of unified series. These include the single 4A series with a rated power range from 0.06 to 400 kW, the machines of which are highly reliable, have good performance and meet world standards.
Autonomous asynchronous generators are three-phase machines that convert the mechanical energy of the primary engine into alternating current electrical energy. Their undoubted advantage over other types of generators is the absence of a commutator-brush mechanism and, as a consequence, greater durability and reliability.
Operation of an asynchronous electric motor in generator mode
If an asynchronous motor disconnected from the network is set into rotation from any prime mover, then in accordance with the reversibility principle electric machines When the synchronous rotation speed is reached, a certain EMF is generated at the terminals of the stator winding under the influence of the residual magnetic field. If you now connect a battery of capacitors C to the terminals of the stator winding, then a leading capacitive current will flow in the stator windings, which in this case is magnetizing.
The battery capacity C must exceed a certain critical value C0, depending on the parameters of the autonomous asynchronous generator: only in this case does the generator self-excite and a three-phase symmetrical voltage system is installed on the stator windings. The voltage value ultimately depends on the characteristics of the machine and the capacitance of the capacitors. Thus, an asynchronous squirrel-cage electric motor can be converted into asynchronous generator.
Standard circuit for connecting an asynchronous electric motor as a generator.
You can select the capacitance so that the rated voltage and power of the asynchronous generator are equal to the voltage and power, respectively, when it operates as an electric motor.
Table 1 shows the capacitor capacities for excitation of asynchronous generators (U=380 V, 750...1500 rpm). Here reactive power Q is determined by the formula:
Q = 0.314 U 2 C 10 -6 ,
where C is the capacitance of the capacitors, μF.
| Generator power, kVA | Idling | |||||
| capacity, µF | reactive power, kvar | cos = 1 | cos = 0.8 | |||
| capacity, µF | reactive power, kvar | capacity, µF | reactive power, kvar | |||
| 2,0 3,5 5,0 7,0 10,0 15,0 |
28 45 60 74 92 120 |
1,27 2,04 2,72 3,36 4,18 5,44 |
36 56 75 98 130 172 |
1,63 2,54 3,40 4,44 5,90 7,80 |
60 100 138 182 245 342 |
2,72 4,53 6,25 8,25 11,1 15,5 |
As can be seen from the above data, the inductive load on the asynchronous generator, which reduces the power factor, causes sharp increase required capacity. To maintain a constant voltage with increasing load, it is necessary to increase the capacitor capacity, that is, connect additional capacitors. This circumstance must be considered as a disadvantage of the asynchronous generator.
The rotation frequency of an asynchronous generator in normal mode must exceed the asynchronous one by a slip value S = 2...10%, and correspond to the synchronous frequency. Failure to comply with this condition will lead to the fact that the frequency of the generated voltage may differ from the industrial frequency of 50 Hz, which will lead to unstable operation of frequency-dependent consumers of electricity: electric pumps, washing machines, devices with a transformer input.
A decrease in the generated frequency is especially dangerous, since in this case the inductive resistance of the windings of electric motors and transformers decreases, which can cause their increased heating and premature failure.
An ordinary asynchronous squirrel-cage electric motor of appropriate power can be used as an asynchronous generator without any modifications. The power of the electric motor-generator is determined by the power of the connected devices. The most energy-intensive of them are:
- household welding transformers;
- electric saws, electric jointers, grain crushers (power 0.3...3 kW);
- electric furnaces of the "Rossiyanka" and "Dream" types with a power of up to 2 kW;
- electric irons (power 850…1000 W).
I would especially like to dwell on the operation of household welding transformers. Their connection to an autonomous source of electricity is most desirable, because when operating from an industrial network, they create a number of inconveniences for other electricity consumers.
If household welding transformer is designed to work with electrodes with a diameter of 2...3 mm, then its total power is approximately 4...6 kW, the power of the asynchronous generator to power it should be within 5...7 kW. If a household welding transformer allows working with electrodes with a diameter of 4 mm, then in the heaviest mode - “cutting” metal, the total power consumed by it can reach 10...12 kW, respectively, the power of an asynchronous generator should be within 11...13 kW.
As a three-phase bank of capacitors, it is good to use so-called reactive power compensators, designed to improve cosφ in industrial lighting networks. Their typical designation: KM1-0.22-4.5-3U3 or KM2-0.22-9-3U3, which is deciphered as follows. KM - cosine capacitors impregnated with mineral oil, the first number is the size (1 or 2), then the voltage (0.22 kV), power (4.5 or 9 kvar), then the number 3 or 2 means three-phase or single-phase version, U3 (temperate climate of the third category).
In case self-made batteries, you should use capacitors such as MBGO, MBGP, MBGT, K-42-4, etc. for an operating voltage of at least 600 V. Electrolytic capacitors cannot be used.
The option discussed above for connecting a three-phase electric motor as a generator can be considered classic, but not the only one. There are other methods that have proven themselves just as well in practice. For example, when a bank of capacitors is connected to one or two windings of an electric motor generator.
Two-phase mode of an asynchronous generator.
Fig.2 Two-phase mode of an asynchronous generator.
This circuit should be used when there is no need to obtain three-phase voltage. This switching option reduces the working capacity of the capacitors, reduces the load on the primary mechanical engine in mode idle speed etc. saves "precious" fuel.
Single-phase asynchronous squirrel-cage electric motors can be used as low-power generators producing alternating single-phase voltage 220 V household use: from washing machines such as "Oka", "Volga", irrigation pumps "Agidel", "BTsN", etc. Their capacitor bank can be connected in parallel to the working winding, or use an existing phase-shifting capacitor connected to the starting winding. The capacity of this capacitor may need to be increased slightly. Its value will be determined by the nature of the load connected to the generator: active loads (electric furnaces, light bulbs, electric soldering irons) require a small capacity, inductive loads (electric motors, televisions, refrigerators) require more.
Fig.3 Low power generator from single-phase asynchronous motor.
Now a few words about the primary mechanical engine, which will drive the generator. As you know, any transformation of energy is associated with its inevitable losses. Their value is determined by the efficiency of the device. Therefore power mechanical engine must exceed the power of the asynchronous generator by 50...100%. For example, with an asynchronous generator power of 5 kW, the power of a mechanical motor should be 7.5...10 kW. Using a transmission mechanism, the speed of the mechanical engine and the generator are matched so that the operating mode of the generator is set at the average speed of the mechanical engine. If necessary, you can briefly increase the power of the generator by increasing the speed of the mechanical engine.
Each autonomous power plant must contain minimum required attachments: AC voltmeter (with a scale up to 500 V), frequency meter (preferably) and three switches. One switch connects the load to the generator, the other two switch the excitation circuit. The presence of switches in the excitation circuit makes it easier to start a mechanical engine, and also allows you to quickly reduce the temperature of the generator windings; after completion of work, the rotor of the unexcited generator is rotated for some time by the mechanical engine. This procedure extends the active life of the generator windings.
If the generator is used to power equipment that is normally connected to the AC mains (for example, residential lighting, household electrical appliances), then it is necessary to provide a two-phase switch, which will turn off the this equipment from the industrial network. It is necessary to disconnect both wires: “phase” and “zero”.
In conclusion, some general advice.
1. The alternator is a hazardous device. Use 380 V only when absolutely necessary; in all other cases, use 220 V.
2. According to safety requirements, the electric generator must be equipped with grounding.
3. Pay attention to the thermal mode of the generator. He "does not like" idling. Reduce thermal load possible by more careful selection of the capacitance of the exciting capacitors.
4. Make no mistake about the amount of electrical current produced by the generator. If one phase is used when operating a three-phase generator, then its power will be 1/3 of the total power of the generator, if two phases - 2/3 of the total power of the generator.
5. The frequency of the alternating current produced by the generator can be indirectly controlled by the output voltage, which in the “no-load” mode should be 4...6% higher than the industrial value of 220/380 V.
The idea of having an autonomous source electrical energy and not depending on the fixed state network worries the minds of many rural residents.
It is quite simple to implement: you need a three-phase asynchronous electric motor, which can be used even from old, decommissioned industrial equipment.
A generator from an asynchronous motor is made with your own hands according to one of the three schemes published in this article. It will convert mechanical energy into electricity freely and reliably.
How to choose an electric motor
To eliminate errors at the project stage, it is necessary to pay attention to the design of the purchased motor, as well as its electrical characteristics: power consumption, supply voltage, rotor speed.
Asynchronous machines are reversible. They are able to operate in the following modes:
· electric motor when external voltage is applied to them;
· or a generator, if their rotor rotates a source of mechanical energy, for example, a water or wind wheel, an internal combustion engine.
We pay attention to the nameplate, the design of the rotor and stator. We take their features into account when creating a generator.
What you need to know about stator design
It has three insulated windings wound on a common magnetic core for power supply from each voltage phase.
They are connected in one of two ways:
1. A star, when all the ends are collected at one point. At 3 starts and general conclusion ends, voltage is supplied through four wires.
2. Triangle - the end of one winding is connected to the beginning of the other so that the circuit is assembled into a ring and only three wires come out of it.
This information is presented in more detail in the article on my website about connecting a three-phase motor to a single-phase household network.
Rotor design features
It also has a magnetic circuit and three windings. They are connected in one of two ways:
1. through the contact terminals of a motor with a wound rotor;
2. short-circuited by an aluminum insert into the squirrel wheel design - asynchronous machines.
We need a squirrel-cage rotor. All circuits are designed for him.
The wound rotor design can also be used as a generator. But it will have to be redone: we simply short-circuit all the outputs to each other.
How to take into account the electrical characteristics of the engine
The operation of the generator will be affected by:
1. Winding wire diameter. The heating of the structure and the amount of applied power directly depend on it.
2. The design speed of the rotor, indicated by the number of revolutions.
3. Method of connecting windings in a star or triangle.
4. The amount of energy loss determined by the efficiency and cosine φ.
We look at them on a plate or calculate them using indirect methods.
How to make an electric motor switch to generator mode
You need to do two things:
1. Spin the rotor from a source of extraneous mechanical power.
2. Excite an electromagnetic field in the windings.
If everything is clear with the first point, then for the second it is enough to connect a bank of capacitors to the windings, creating a capacitive load of a certain size.
Several variants of schemes have been developed for this issue.
Full star
Capacitors are included between each pair of windings.
Simplified star
In this circuit, the starting and running capacitors are connected by their own switches.
Triangle diagram
Capacitors are connected in parallel to each winding. A linear voltage of 220 volts is created at the output terminals.
What capacitor ratings are needed?
The easiest way is to use paper capacitors with voltages of 500 volts and above. It is better not to use electrolytic models: they can boil and explode.
The formula for determining capacity is:С=Q/2π∙f∙U2.
In it, Q is reactive power, f is frequency, U is voltage.
Electric generators are an additional source of energy for the home. If the main power grids are far away, it may well replace them. Frequent power outages force the installation of alternating current generators.
They are not cheap, is there any point in spending more than 10,000 rubles? for the device, if you can make a generator from an electric motor yourself? Of course, some electrical engineering skills and tools will be useful for this. The main thing is that you don’t have to spend money.
You can assemble a simple generator with your own hands; it will be relevant if you need to cover a temporary shortage of electricity. It is not suitable for more serious cases, as it does not have sufficient functionality and reliability.
Naturally, there are many difficulties in the manual assembly process. Required parts and tools may not be available. Lack of experience and skills in such work can be intimidating. But a strong desire will be the main incentive and will help overcome all labor-intensive procedures.
Implementation of the generator and its operating principle
Due to electromagnetic induction, a electric current. This happens because the winding moves in an artificially created magnetic field. This is the principle of operation of an electric generator.
The generator is driven by a low-power internal combustion engine. It can run on gasoline, gas or diesel fuel.
An electric generator has a rotor and a stator. The magnetic field is created using a rotor. Magnets are attached to it. The stator is the stationary part of the generator, and consists of special steel plates and a coil. There is a small gap between the rotor and stator.
There are two types of electric generator. The first has synchronous rotor rotation. He has complex design, and low efficiency. In the second type, the rotor rotates asynchronously. The principle of operation is simple.
Asynchronous motors lose a minimum of energy, while in synchronous generators the loss rate reaches 11%. Therefore, electric motors with asynchronous rotor rotation are very popular in household appliances and in various factories.
During operation, voltage surges may occur, which have a detrimental effect on household appliances. For this purpose, there is a rectifier at the output ends.
The asynchronous generator is easy to use maintenance. Its body is reliable and sealed. You don’t have to worry about household appliances that have an ohmic load and are sensitive to voltage surges. High efficiency, and a long period of operation, make the device in demand, and besides, it can be assembled independently.
What will you need to assemble the generator? First, you need to choose a suitable electric motor. It can be taken from washing machine. There is no need to make a stator yourself; it is better to use ready-made solution, where there are windings.
It’s a good idea to immediately stock up on enough copper wires, and insulating materials. Since any generator will produce voltage surges, a rectifier will be needed.
According to the instructions for the generator, you need to do a power calculation yourself. In order for the future device to produce the required power, it needs to be given a speed slightly higher than the rated power.
Let's use a tachometer and turn on the engine, so you can find out the speed of rotation of the rotor. You need to add 10% to the resulting value, this will prevent the engine from overheating.
Capacitors will help maintain the required voltage level. They are selected depending on the generator. For example, for a power of 2 kW, a capacitor capacity of 60 μF will be required. You need 3 such parts with the same capacity. To make the device safe, it must be grounded.
Build process
Everything is simple here! Capacitors are connected to the electric motor in a delta configuration. During operation, you need to periodically check the temperature of the case. Its heating may occur due to incorrectly selected capacitors.
A homemade generator that does not have automation must be constantly monitored. Heating that occurs over time will reduce efficiency. Then the device needs to be given time to cool down. From time to time you should measure the voltage, speed, and current.
Incorrectly calculated characteristics are not able to provide the equipment with the necessary power. Therefore, before starting assembly, you should carry out drawing work and stock up on diagrams.
It is quite possible that homemade device will accompany frequent breakdowns. This should not be surprising, since it is practically impossible to achieve a hermetically sealed installation of all elements of an electric generator at home.
So, I hope it’s now clear how to make a generator from an electric motor. If you want to design a device whose power should be enough to operate simultaneously household appliances And lighting lamps, or construction tools, then you need to add up their power and select the desired engine. It is desirable that it has a small power reserve.
If at manual assembly the electric generator failed, do not despair. There are many modern models on the market that do not require constant supervision. They can be of different power, and are quite economical. There are photos of generators on the Internet; they will help you estimate the dimensions of the device. The only negative is their high cost.
Photos of DIY generators
Purchasing a factory generator is not always advisable. Sometimes it's easier to use available materials and tools to make it yourself. A device with a power of up to 1 kW will be enough to connect street lighting at the dacha or any other household appliances. You can build such a generator from an asynchronous motor.
Making an asynchronous generator with your own hands provides many advantages. It is a free source of electricity that can be used for various purposes. Moreover, even a novice master can do such work.
Structurally diagram of the electric generator will consist of several key elements:
How the device works
The operating principle of homemade 220 V alternating current generators is no different from devices that are used for industrial purposes. Both convert kinetic energy into electrical energy.
In DIY designs, the force of the wind turns the windmill, which is mounted on a rotor. Thus, kinetic energy is transferred to the generator. It produces electricity. A converted asynchronous motor is often used as a generator.
The electricity generated by the generator is transferred to batteries. The latter must be equipped with a charge control module. Electricity from the batteries is supplied to the DC inverter. In this way, an alternating voltage can be created. It will be suitable for use for domestic purposes, that is, with parameters of 220 V and 50 Hz.
To convert AC voltage to DC, you need to install a special controller. It is thanks to him that the batteries are charged. Sometimes inverters can act as a source uninterruptible power supply. That is, in the absence of centralized electricity or interruptions in its operation, an asynchronous alternating current generator can be used for domestic purposes, powering various devices operating on 220 V.
Required materials and tools
To make a motor-generator with your own hands, it is enough to have an antisynchronous motor. The rest of the materials can be found on the farm or in specialized radio markets.
The following tools and materials may be needed:
First you need to decide on the desired final result. The characteristics of the electric motor that acts as a generator can be different, and this determines how much electricity the device will generate per unit of time.
To produce an average amount of energy the generator should have approximately the following characteristics:
- The minimum installation power is 1.3 kW.
- Neodymium magnets in the design are desirable. Their function is to provide electromagnetic driving force. For this purpose, a steel sleeve can be used, which is installed on the rotor.
- The location of the magnets on the rotor must correspond to the diagram. This means that their poles must be turned in the correct direction.
- The rotor shaft must first be ground and adjusted to the diameter of the magnets.
- When installing magnets, it is not always necessary to redo the winding. If it consists of wires with a large cross-section, it’s okay, it will only increase the power. The most the best option The winding will be a device having six poles, a wire with a cross-section of no more than 1.2 mm and a maximum of 24 turns on the coil.
Installation nuances
As a rule, to make a wind generator from an asynchronous motor with your own hands a windmill with three blades is used, which reach two meters in diameter. If you increase the number of blades or their length, the performance will not improve. Before choosing a device modification, type, characteristics, dimensions, it is necessary to carry out the correct calculation.
Each device must be connected to the mains in a certain order. First come the batteries, and then the wind generator. The electric motor shaft can rotate either horizontally or vertically. Typically installed in a vertical position, this is due to design features. To ensure protection from moisture, the generator is equipped with gaskets or a cap.
To install the mast you must select open place where will it be maximum quantity winds. The installation height of the generator device must be high enough. Converted asynchronous in ideal is installed at a height of 15 meters, but in practice no one uses masts over 7 meters.
It is better not to use the device as the main source of electrical power at home. Such a low-speed device should be installed to insure against situations with power outages or to save the family budget, since the bill centralized supply decreases significantly.
It is worth noting that installations of this type cannot be used in all regions. The minimum wind speed for practical use should always be kept at around 7 meters per second. If this figure is less, then very little electricity will be generated.
Before installation necessary calculations. In some situations, difficulties may arise with processing asynchronous engine nodes. A windmill cannot be manufactured without the appropriate modules, as well as preliminary testing of the device. It is impossible to connect such equipment.
Of course, you can buy a factory-made asynchronous generator, but the DIY option is much more economical and does not take much time. The process should not have any difficulties even for an inexperienced person.
To remake a brushed AC motor, you need to prepare some tools. The work must be done taking into account certain rules:
The generator can also be taken from other devices, for example, from a VAZ car. After this, you need to proceed to its installation on the mast. It should be remembered that if a rotor operating in squirrel-cage mode is used, the device will produce high voltage current.
To obtain 220 volts, the device should be equipped with a step-down transformer. The device does not need to be connected to the mains, since it operates using the self-powering method.
Thus, making a generator from an asynchronous motor is not challenging task even for a novice master. If we take into account all the capabilities of the device, we can conclude that in certain situations it will help with power outages, and if a very powerful wind generator is installed, it will be the main source of energy in the house.
The energy of the electric current, entering the inside of an asynchronous motor, easily turns into motion energy at the exit from it. But what if a reverse transformation is required? In this case, you can build homemade generator from an asynchronous motor. It will only function in a different mode: by performing mechanical work electricity will begin to be generated. The perfect solution– transformation into a wind generator – a source of free energy.
It has been experimentally proven that a magnetic field is created by an alternating electric field. This is the basis of the operating principle of an asynchronous motor, the design of which includes:
- The body is what we see from the outside;
- Stator is the stationary part of the electric motor;
- A rotor is an element that is driven.
At the stator main element– a winding to which alternating voltage is applied (the principle of operation is not on permanent magnets, but on a magnetic field that is damaged by alternating electric). The rotor is a cylinder with slots in which the winding is placed. But the current entering it has the opposite direction. As a result, two variables are formed electric fields. Each of them creates a magnetic field, which begins to interact with each other. But the design of the stator is such that it cannot move. Therefore, the result of the interaction of two magnetic fields is the rotation of the rotor.
Design and principle of operation of the electric generator
Experiments also confirm that the magnetic field creates an alternating electric field. Below is a diagram that clearly illustrates the principle of operation of the generator.
If a metal frame is placed and rotated in a magnetic field, the magnetic flux penetrating it will begin to change. This will lead to the formation of an induced current inside the frame. If you connect the ends to a current consumer, for example, to an electric lamp, you can observe its glow. This suggests that the mechanical energy expended in rotating the frame within the magnetic field was converted into electrical energy, which helped light the lamp.
Structurally, an electric generator consists of the same parts as an electric motor: a housing, a stator and a rotor. The difference lies only in the principle of operation. The rotor is driven by the magnetic field created by the electric field in the stator winding. And an electric current appears in the stator winding due to a change in the magnetic flux penetrating it, due to the forced rotation of the rotor.
From electric motor to electric generator
Human life today is unthinkable without electricity. Therefore, power plants are being built everywhere, converting the energy of water, wind and atomic nuclei into electrical energy. It has become universal because it can be converted into the energy of movement, heat and light. This became the reason for the massive spread of electric motors. Electric generators are less popular because the state supplies electricity centrally. But still, sometimes it happens that there is no electricity and there is nowhere to get it from. In this case, a generator from an asynchronous motor will help you.
We have already said above that the electric generator and the engine are structurally similar to each other. This raises the question: is it possible to use this miracle of technology as a source of both mechanical and electrical energy? It turns out that it is possible. And we will tell you how to convert a motor into a current source with your own hands.
The meaning of the rework
If you need an electric generator, why make it from an engine if you can buy new equipment? However, high-quality electrical equipment is not a cheap pleasure. And if you have one that is not used in at the moment motor, why shouldn't it serve him well? By simple manipulations and minimal costs you will get an excellent current source that can power devices with active loads. These include computer, electronic and radio equipment, ordinary lamps, heaters and welding converters.
But savings are not the only advantage. Advantages of an electric current generator constructed from an asynchronous electric motor:
- The design is simpler than that of a synchronous analogue;
- Maximum protection of the insides from moisture and dust;
- High resistance to overloads and short circuits;
- Almost complete absence nonlinear distortions;
- Clearance factor (a value expressing the uneven rotation of the rotor) no more than 2%;
- The windings are static during operation, so they do not wear out for a long time, increasing their service life;
- The generated electricity immediately has a voltage of 220V or 380V, depending on which engine you decide to convert: single-phase or three-phase. This means that current consumers can be directly connected to the generator, without inverters.
Even if the electric generator cannot fully meet your needs, it can be used in conjunction with a centralized power supply. In this case, we are again talking about saving: you will have to pay less. The benefit will be expressed as the difference obtained by subtracting the electricity generated from the amount of electricity consumed.
What is needed for remodeling?
To make a generator from an asynchronous motor with your own hands, you must first understand what is preventing the conversion of electrical energy from mechanical energy. Let us recall that for the formation of an induction current, the presence of a magnetic field that changes with time is necessary. When the equipment operates in motor mode, it is created in both the stator and the rotor due to power from the network. If you switch the equipment to generator mode, it turns out that there is no magnetic field at all. Where does he come from?
After the equipment operates in motor mode, the rotor retains residual magnetization. It is this force that causes an induced current in the stator due to forced rotation. And in order for the magnetic field to be maintained, it will be necessary to install capacitors that carry capacitive current. It is he who will maintain magnetization due to self-excitation.
We have sorted out the question of where the original magnetic field came from. But how to set the rotor in motion? Of course, if you spin it with your own hands, you can power a small light bulb. But the result is unlikely to satisfy you. The ideal solution is to turn the motor into a wind generator, or windmill.
This is the name of a device that converts the kinetic energy of the wind into mechanical, and then into electrical. Wind generators are equipped with blades that move when they meet the wind. They can rotate in both vertical and horizontal planes.
From theory to practice
Let's build a wind generator from a motor with our own hands. For easy understanding, diagrams and videos are included with the instructions. You will need:
- Device for transmitting wind energy to the rotor;
- Capacitors for each stator winding.
It is difficult to formulate a rule according to which you could choose a wind catching device the first time. Here you need to be guided by the fact that when the equipment is operating in generator mode, the rotor speed should be 10% higher than when operating as an engine. You need to take into account not the nominal frequency, but the idle speed. Example: the rated frequency is 1000 rpm, and in idle mode it is 1400. Then to generate current you will need a frequency of approximately 1540 rpm.
The selection of capacitors by capacity is made according to the formula:
C is the required capacity. Q – rotor rotation speed in revolutions per minute. P is the number “pi” equal to 3.14. f – phase frequency (constant value for Russia, equal to 50 Hertz). U – network voltage (220 if one phase, and 380 if three).
Calculation example : Three-phase rotor rotates at 2500 rpm. ThenC = 2500/(2*3.14*50*380*380)=56 µF.
Attention! Do not select a container larger than the calculated value. Otherwise, the active resistance will be high, which will lead to overheating of the generator. This can also happen when the device is started without load. In this case, it will be useful to reduce the capacitance of the capacitor. To make it easy to do it yourself, place the container not as a whole, but as a prefabricated one. For example, 60 μF can be made up of 6 pieces of 10 μF connected in parallel to each other.
How to connect?
Let's look at how to make a generator from an asynchronous motor, using the example of a three-phase motor:
- Connect the shaft to a device that rotates the rotor using wind energy;
- Connect the capacitors in a triangle pattern, the vertices of which are connected to the ends of the star or the vertices of the stator triangle (depending on the type of winding connection);
- If a voltage of 220 Volts is required at the output, connect the stator windings in a triangle (the end of the first winding with the beginning of the second, the end of the second with the beginning of the third, the end of the third with the beginning of the first);
- If you need to power devices from 380 Volts, then a star circuit is suitable for connecting the stator windings. To do this, connect the beginning of all windings together, and connect the ends to the appropriate containers.
Step-by-step instructions on how to make a low-power single-phase wind generator with your own hands:
- Get it out of the old one washing machine electric motor;
- Determine the working winding and connect a capacitor in parallel with it;
- Ensure that the rotor rotates using wind energy.
You will get a windmill, like in the video, and it will produce 220 Volts.
For electrical appliances powered by DC, you will additionally need to install a rectifier. And if you are interested in monitoring the power supply parameters, install an ammeter and a voltmeter at the output.
Advice! Due to the lack of constant wind, wind generators may sometimes stop working or not work at full capacity. Therefore, it is convenient to organize your own power plant. To do this, the windmill is connected to the battery during windy weather. The accumulated electricity can be used during calm periods.
An electric motor is a device that acts as an energy converter and operates in the mode of obtaining mechanical energy from electrical energy. Through simple transformations without the use of a permanent magnet, but thanks to residual magnetization, the motor begins to work as a power source. These are two mutually inverse phenomena that help you save: you don’t need to buy a wind generator if an electric motor is lying around idle. Watch the video and learn.