There are situations in life when you need to connect some industrial equipment to a regular home power supply network. A problem immediately arises with the number of wires. Machines intended for use in enterprises usually have three, but sometimes four, terminals. What to do with them, where to connect them? Those who tried various options, we were convinced that the motors just didn’t want to spin. Is it even possible to connect a single-phase three-phase motor? Yes, you can achieve rotation. Unfortunately, in this case, a decrease in power by almost half is inevitable, but in some situations this is the only way out.

Voltages and their ratio

In order to understand how to connect a three-phase motor to a regular outlet, you need to understand how the voltages in the industrial network relate. The voltage values are well known - 220 and 380 Volts. Previously, there was still 127 V, but in the fifties this parameter was abandoned in favor of a higher one. Where did these “magic numbers” come from? Why not 100, or 200, or 300? It seems that round numbers are easier to count.

Most industrial electrical equipment is designed to be connected to a three-phase network. The voltage of each phase in relation to the neutral wire is 220 Volts, just like in a home socket. Where does 380 V come from? It is very simple, just consider an isosceles triangle with angles of 60, 30 and 30 degrees, which is a vector stress diagram. The length of the longest side will be equal to the length of the thigh multiplied by cos 30°. After some simple calculations, you can make sure that 220 x cos 30° = 380.

Three-phase motor device

Not all types of industrial motors can operate from one phase. The most common of them are the “workhorses” that make up the majority of electrical machines in any enterprise - asynchronous machines with a power of 1 - 1.5 kVA. How does such a three-phase motor work in the three-phase network for which it is intended?

The inventor of this revolutionary device was the Russian scientist Mikhail Osipovich Dolivo-Dobrovolsky. This outstanding electrical engineer was a proponent of the theory of a three-phase power supply network, which has become dominant in our time. three-phase operates on the principle of induction of currents from the stator windings to closed rotor conductors. As a result of their flow through the short-circuited windings, a magnetic field arises in each of them, interacting with the stator power lines. This produces a torque that leads to circular motion of the motor axis.

The windings are angled 120° so that the rotating field generated by each phase pushes each magnetized side of the rotor in succession.

Triangle or star?

A three-phase motor in a three-phase network can be switched on in two ways - with or without a neutral wire. The first method is called “star”, in this case each of the windings is under (between phase and zero), equal in our conditions to 220 V. The connection diagram of a three-phase motor with a “triangle” involves connecting three windings in series and applying linear (380 V) voltage to switching nodes. In the second case, the engine will produce about one and a half times more power.

How to turn the motor in reverse?

Control of a three-phase motor may require changing the direction of rotation to the opposite, that is, reverse. To achieve this, you just need to swap two of the three wires.

To make it easier to change the circuit, jumpers are provided in the motor terminal box, usually made of copper. For star switching, gently connect the three output wires of the windings together. The “triangle” turns out to be a little more complicated, but any average qualified electrician can handle it.

Phase shifting tanks

So, sometimes the question arises about how to connect a three-phase motor to a regular home outlet. If you just try to connect two wires to the plug, it will not rotate. In order for things to work, you need to simulate the phase by shifting the supplied voltage by some angle (preferably 120°). This effect can be achieved by using a phase-shifting element. Theoretically, this could be inductance or even resistance, but most often a three-phase motor in a single-phase network is switched on using electrical circuits designated by the Latin letter C on the diagrams.

As for the use of chokes, it is difficult due to the difficulty of determining their value (if it is not indicated on the device body). To measure the value of L, a special device or a circuit assembled for this purpose is required. In addition, the choice of available chokes is usually limited. However, any phase-shifting element can be selected experimentally, but this is a troublesome task.

What happens when you turn on the engine? Zero is applied to one of the connection points, phase is applied to the other, and a certain voltage is applied to the third, shifted by a certain angle relative to the phase. It is clear to a non-specialist that the operation of the engine will not be complete in terms of mechanical power on the shaft, but in some cases the very fact of rotation is sufficient. However, already at startup, some problems may arise, for example, the lack of an initial torque capable of moving the rotor from its place. What to do in this case?

Start capacitor

At the moment of starting, the shaft requires additional efforts to overcome the forces of inertia and static friction. To increase the torque, you should install an additional capacitor, connected to the circuit only at the moment of start, and then turned off. For these purposes the best option is the use of a closing button without fixing the position. The connection diagram for a three-phase motor with a starting capacitor is shown below, it is simple and understandable. At the moment the voltage is applied, press the “Start” button, and it will create an additional phase shift. After the engine spins up to the required speed, the button can (and even should) be released, and only the working capacity will remain in the circuit.

Calculation of container sizes

So, we found out that in order to turn on a three-phase motor in a single-phase network, an additional connection circuit is required, which, in addition to the start button, includes two capacitors. You need to know their value, otherwise the system will not work. First, let's determine the amount of electrical capacitance required to make the rotor move. When connected in parallel, it is the sum:

C = C st + Wed, where:

C st - starting additional capacity that can be switched off after takeoff;

C p is a working capacitor that provides rotation.

We also need the value of the rated current I n (it is indicated on the plate attached to the engine at the manufacturer). This parameter can also be determined using a simple formula:

I n = P / (3 x U), where:

U - voltage, when connected as a “star” - 220 V, and if connected as a “triangle”, then 380 V;

P is the power of a three-phase motor; sometimes, if the plate is lost, it is determined by eye.

So, the dependencies of the required operating power are calculated using the formulas:

C p = Wed = 2800 I n / U - for the “star”;

C p = 4800 I n / U - for a “triangle”;

The starting capacitor should be 2-3 times larger than the working capacitor. The unit of measurement is microfarads.

There is also a very simple way to calculate capacity: C = P /10, but this formula gives the order of the number rather than its value. However, in any case you will have to tinker.

Why adjustment is needed

The calculation method given above is approximate. Firstly, the nominal value indicated on the body of the electrical capacitance may differ significantly from the actual one. Secondly, paper capacitors (generally speaking, an expensive thing) are often used second-hand, and they, like any other items, are subject to aging, which leads to an even greater deviation from the specified parameter. Thirdly, the current that will be consumed by the motor depends on the magnitude of the mechanical load on the shaft, and therefore it can only be assessed experimentally. How to do this?

This requires a little patience. The result can be a rather voluminous set of capacitors. The main thing is to secure everything well after finishing the work so that the soldered ends do not fall off due to vibrations emanating from the motor. And then it would be a good idea to analyze the result again and, perhaps, simplify the design.

Composing a battery of containers

If the master does not have at his disposal special electrolytic clamps that allow you to measure the current without opening the circuits, then you should connect an ammeter in series to each wire that enters the three-phase motor. In a single-phase network, the total value will flow, and by selecting capacitors one should strive for the most uniform loading of the windings. It should be remembered that when connected in series, the total capacitance decreases according to the law:

It is also necessary not to forget about such an important parameter as the voltage for which the capacitor is designed. It must be no less than the nominal value of the network, or better yet, with a margin.

Discharge resistor

The circuit of a three-phase motor connected between one phase and a neutral wire is sometimes supplemented with resistance. It serves to prevent the charge that remains on the starting capacitor from accumulating after the machine has already been turned off. This energy can cause an electric shock, which is not dangerous, but extremely unpleasant. In order to protect yourself, you should connect a resistor in parallel with the starting capacitance (electricians call this “bypassing”). The value of its resistance is large - from half a megohm to a megohm, and it is small in size, so half a watt of power is enough. However, if the user is not afraid of being “pinched,” then it is quite possible to do without this detail.

Using Electrolytes

As already noted, film or paper electrical containers are expensive, and purchasing them is not as easy as we would like. It is possible to make a single-phase connection to a three-phase motor using inexpensive and readily available electrolytic capacitors. At the same time, they won’t be very cheap either, since they must withstand 300 Volts DC. For safety, they should be shunted with semiconductor diodes (D 245 or D 248, for example), but it would be useful to remember that when these devices break through, alternating voltage will hit the electrolyte, and it will first heat up very much, and then explode, loudly and effectively. Therefore, unless absolutely necessary, it is better to use paper-type capacitors that operate under either constant or alternating voltage. Some craftsmen completely allow the use of electrolytes in starting circuits. Due to short-term exposure to alternating voltage, they may not have time to explode. It's better not to experiment.

If there are no capacitors

Where do ordinary citizens who do not have access to in-demand electrical and electronic parts purchase them? At flea markets and flea markets. There they lie, carefully soldered by someone’s (usually elderly) hands from old washing machines, televisions and other household and industrial equipment that are out of use and out of use. They ask a lot for these Soviet-made products: sellers know that if a part is needed, they will buy it, and if not, they will not take it for nothing. It happens that just the most necessary thing (in this case, a capacitor) is not there. So what should we do? No problem! Resistors will also do, you just need powerful ones, preferably ceramic and vitrified ones. Of course, ideal resistance (active) does not shift the phase, but nothing is ideal in this world, and in our case this is good. Every physical body has its own inductance, electrical power and resistivity, whether it is a tiny speck of dust or a huge mountain. Connecting a three-phase motor to a power outlet becomes possible if in the above diagrams you replace the capacitor with a resistance, the value of which is calculated by the formula:

R = (0.86 x U) / kI, where:

kI - current value for three-phase connection, A;

U - our trusty 220 Volts.

What engines are suitable?

Before purchasing a motor for a lot of money, which a zealous owner intends to use as a drive for a grinding wheel, circular saw, drilling machine or any other useful household device, it would not hurt to think about its applicability for these purposes. Not every three-phase motor in a single-phase network will be able to operate at all. For example, the MA series (it has a squirrel-cage rotor with a double cage) should be excluded so that you do not have to carry considerable and useless weight home. In general, it is best to experiment first or invite an experienced person, an electrician, for example, and consult with him before purchasing. A three-phase asynchronous motor of the UAD, APN, AO2, AO and, of course, A series is quite suitable. These indices are indicated on the nameplates.

A torque quite sufficient to start the indicated electric motors from a single-phase 220 V/50 Hz network can be obtained by shifting the currents in phase in the phase windings of the electric motor, using for this purpose bidirectional electronic switches, which are turned on at a certain time.

The first circuit (Fig. 1) is intended for starting electric motors with a rated rotation speed equal to or less than 1500 rpm, the windings of which are connected in a triangle. This scheme was based on the diagram, which was simplified to the limit. In this circuit, an electronic switch (triac VS1) provides a current shift in the winding “C9raquo; at a certain angle (50. 70°), which provides sufficient torque.

The second circuit (Fig. 2) is intended for starting electric motors with a rated rotation speed of 3000 rpm, as well as for electric motors operating mechanisms with a high resistance moment during starting. In these cases, a significantly larger starting torque is required. Therefore, an “open star” connection scheme for the EM windings was used (Fig. 14, c), which provides maximum starting torque. In the indicated circuit, the phase-shifting capacitors are replaced by two electronic switches. One switch is connected in series with the phase winding “A9raquo; and creates in it “inductive9raquo; (lagging)

Capacitorless starting of three-phase electric motors from a single-phase network Capacitorless starting of three-phase electric motors from a single-phase network
current shift, the second is connected in parallel to the phase winding “B9raquo; and creates a “capacitive” in it (leading) current shift. What is taken into account here is that the EM windings themselves are displaced in space by 120 electrical degrees relative to each other.
Voltage is supplied to the electric motor by a manual push-button starter. type PNVS-10, through the middle pole of which a phase-shifting chain is connected. The middle pole contacts are closed only when the “Start” button is pressed.
By pressing the “Start” button, by rotating the trimmer resistance R2, the required starting torque is selected. This is what you do when setting up the circuit shown in Fig. 2.
When setting up the circuit in Fig. 1, due to the passage of large starting currents, the electric motor hums and vibrates strongly for some time (before turning around). In this case, it is better to change the value of R2 in steps when the voltage is removed, and then, by briefly applying voltage, check how the EM starts. If the voltage shift angle is far from optimal, then the ED hums and vibrates very strongly. As it approaches the optimal angle, the engine “tries9raquo; rotate in one direction or the other, and when optimal it starts quite well.
The author debugged the circuit shown in Fig. 1 on an electric motor of 0.75 kW 1500 rpm and 2.2 kW 1500 rpm, and the circuit shown in Fig. 2 on an electric motor 2.2 kW 3000 rpm .

220 V. By changing the value of R, you need to set the voltage on the lamp to 170 V (for the circuit in Fig. 1) and 100 V (for the circuit in Fig. 2). These voltages were measured by a pointer instrument of the magnetoelectric system, although the voltage shape across the load is not sinusoidal.

tmp5A24-4

V.V. Burloko, Moriupol
Literature
1. // Signal. - 1999. - No. 4.

As is known, for starting a three-phase electric motor(ED) with a squirrel-cage rotor from a single-phase network, a capacitor is most often used as a phase-shifting element. In this case, the capacity of the starting capacitor should be several times greater than the capacity of the working capacitor. For electric motors most often used in households (0.5 - 3 kW), the cost of starting capacitors is comparable to the cost of an electric motor. Therefore, it is desirable to avoid the use of expensive starting capacitors that only work for a short time. At the same time, the use of workers that are constantly on phase shifting capacitors can be considered appropriate, since they allow you to load the engine at 75. 85% of its power when switched on 3-phase (without capacitors its power is reduced by about 50%).

Based on this, to launch 3-phase electric motors from a single-phase network, the author developed and debugged two simple circuits. Both schemes were tested on an electric motor with a power of 0.5. 2.2 kW and showed very good results (start-up time is not much longer than in three-phase mode). The circuits use triacs controlled by pulses of different polarities and a symmetrical dinistor, which generates control signals during each half-cycle of the supply voltage.

The first circuit (Fig. 1) is intended for starting electric motors with a rated rotation speed equal to or less than 1500 rpm, the windings of which are connected in a triangle. This scheme was based on the diagram, which was simplified to the limit. In this circuit, an electronic switch (triac VS1) ensures a current shift in winding “C” by a certain angle (50. 70°), which provides sufficient torque.

The phase shifting device is an RC circuit. By changing resistance R2, a voltage is obtained on capacitor C that is shifted relative to the supply voltage by a certain angle. A symmetrical dinistor VS2 is used as a key element in the circuit. At the moment when the voltage on the capacitor reaches the switching voltage of the dinistor, it will connect the charged capacitor to the control terminal of the triac VS1 and turn on this bidirectional power switch.

The second circuit (Fig. 2) is intended for starting electric motors with a rated rotation speed of 3000 rpm, as well as for electric motors operating mechanisms with a high resistance moment during starting. In these cases, a significantly larger starting torque is required. Therefore, an “open star” connection scheme for the EM windings was used (Fig. 14, c), which provides maximum starting torque. In the indicated circuit, the phase-shifting capacitors are replaced by two electronic switches. One switch is connected in series with the winding of phase “A” and creates an “inductive” (lagging) in it.

current shift, the second is connected in parallel to the winding of phase “B” and creates a “capacitive” (advanced) current shift in it. What is taken into account here is that the EM windings themselves are displaced in space by 120 electrical degrees relative to each other.

The adjustment consists of selecting the optimal angle of current shift in the phase windings, at which the electric motor is reliably started. This can be done without the use of special devices. It is performed as follows.

Voltage is supplied to the electric motor by a push-type “manual” starter PNVS-10, through the middle pole of which a phase-shifting chain is connected. The middle pole contacts are closed only when the “Start” button is pressed.

By pressing the “Start” button, by rotating the trimmer resistance R2, the required starting torque is selected. This is what you do when setting up the circuit shown in Fig. 2.

When setting up the circuit in Fig. 1, due to the passage of large starting currents, the electric motor hums and vibrates strongly for some time (before turning around). In this case, it is better to change the value of R2 in steps when the voltage is removed, and then, by briefly applying voltage, check how the EM starts. If the voltage shift angle is far from optimal, then the ED hums and vibrates very strongly. As it approaches the optimal angle, the engine “tries” to rotate in one direction or another, and at the optimal angle it starts quite well.

At the same time, it has been experimentally established that it is possible to select the values of R and C of the phase-shifting chain corresponding to the optimal angle in advance. To do this, you need to connect a 60 W incandescent lamp in series with a key (triac) and plug them into the network

220 V. By changing the value of R, you need to set the voltage on the lamp to 1 70 V (for the circuit in Fig. 1) and 1 00 V (for the circuit in Fig. 2). These voltages were measured by a pointer instrument of the magnetoelectric system, although the voltage shape across the load is not sinusoidal.

It should be noted that optimal current shift angles can be achieved with various combinations of values of R and C of the phase-shifting chain, i.e. By changing the capacitance value of the capacitor, you will have to select the corresponding resistance value.

Experiments were carried out with triacs TS-2-10 and TS-2-25 without radiators. They worked very well in this scheme. You can also use other triacs with bipolar control for the corresponding operating currents and voltage class not lower than 7. When using imported triacs in a plastic case, they should be installed on radiators.

The symmetrical DB3 dinistor can be replaced with the domestic KR1125. It has a slightly lower switching voltage. Perhaps this is better, but this dinistor is very difficult to find on sale.

Capacitors C are any non-polar, designed for operating voltage at least 50 V (preferably 100 V). You can also use two polar capacitors connected in back-to-back series (in the circuit in Fig. 2, their nominal value should be 3.3 μF each).

The appearance of the electric drive of the grass chopper with the described start-up circuit and 2.2 kW 3000 rpm motor is shown in photo 1.

V.V. Burloko, Moriupol

1. // Signal. - 1999. - No. 4.

2. S.P. Fursov Use of three-phase

electric motors in everyday life. - Chisinau: Cartea

How to connect a 380V to 220V electric motor

Before starting work, understand the design of the IM (induction motor).

The device consists of two elements - a rotor (moving part) and a stator (fixed unit).

The stator has special grooves (recesses) into which the winding is placed, distributed in such a way that the angular distance is 120 degrees.

The windings of the device create one or more pairs of poles, the number of which determines the frequency with which the rotor can rotate, as well as other parameters of the electric motor - efficiency, power and other parameters.

When an asynchronous motor is connected to a three-phase network, current flows through the windings at different time intervals.

A magnetic field is created that interacts with the rotor winding and causes it to rotate.

In other words, a force appears that turns the rotor at different time intervals.

If you connect the blood pressure to a network with one phase (without performing preparatory work), current will appear in only one winding.

The torque generated will not be enough to move the rotor and keep it spinning.

That is why, in most cases, the use of starting and operating capacitors is required to ensure the operation of a three-phase motor. But there are other options.

How to connect an electric motor from 380 to 220V without a capacitor?

As noted above, to start an electric motor with a squirrel-cage rotor from a single-phase network, a capacitor is most often used.

It is this that ensures the device starts at the first moment after the single-phase current is supplied. In this case, the capacity of the starting device should be three times higher than the same parameter for the working capacity.

For motors with a power of up to 3 kilowatts and used at home, the price of starting capacitors is high and sometimes comparable to the cost of the motor itself.

Consequently, many are increasingly avoiding containers used only at the moment of start-up.

The situation is different with working capacitors, the use of which allows you to load the motor at 80-85 percent of its power. If they are absent, the power indicator may drop to 50 percent.

However, capacitorless starting of a 3-phase motor from a single-phase network is possible thanks to the use of bidirectional switches that operate for short periods of time.

The required torque is provided by the displacement of phase currents in the windings of the IM.

Today, two schemes are popular, suitable for motors with power up to 2.2 kW.

It is interesting that the start-up time of the IM from a single-phase network is not much lower than in the usual mode.

The main elements of the circuit are triacs and symmetrical dinistors. The first are controlled by multi-polar pulses, and the second by signals coming from the half-cycle of the supply voltage.

Suitable for 380 Volt electric motors up to 1,500 rpm with delta windings.

The RC circuit acts as a phase-shifting device. By changing the resistance R2, it is possible to achieve a voltage across the capacitor that is shifted by a certain angle (relative to the household network voltage).

The main task is performed by the symmetrical dinistor VS2, which at a certain point in time connects a charged capacitance to the triac and activates this switch.

Suitable for electric motors with a rotation speed of up to 3000 rpm and for motors with increased resistance at start-up.

Such motors require more starting current, so an open star circuit is more relevant.

A special feature is the use of two electronic switches that replace phase-shifting capacitors. During the adjustment process, it is important to ensure the required shift angle in the phase windings.

This is done as follows:

Voltage is supplied to the electric motor through a manual starter (it must be connected in advance).
After pressing the button, you need to select the starting moment using resistor R

When implementing the considered schemes, it is worth considering a number of features:

For the experiment, radiatorless triacs (types TS-2-25 and TS-2-10) were used, which showed excellent results. If you use triacs on a plastic case (imported), you cannot do without radiators.
A symmetrical DB3 type dinistor can be replaced with a KP. Despite the fact that the KP1125 is made in Russia, it is reliable and has a lower switching voltage. The main drawback is the scarcity of this dinistor.

How to connect via capacitors

First, decide which circuit is assembled on the ED. To do this, open the bar cover where the blood pressure terminals are output, and see how many wires come out of the device (most often there are six).

The designations are as follows: C1-C3 are the beginnings of the winding, and C4-C6 are its ends. If the beginnings or ends of the windings are combined with each other, this is a “star”.

The most difficult situation is if six wires simply come out of the case. In this case, you need to look for the corresponding designations on them (C1-C6).

To implement a scheme for connecting a three-phase electric motor to a single-phase network, two types of capacitors are required - starting and working.

The first ones are used to start the electric motor at the first moment. As soon as the rotor spins to the required number of revolutions, the starting capacitance is excluded from the circuit.

If this does not happen, there may be serious consequences, including engine damage.

The main function is performed by working capacitors. Here it is worth considering the following points:

Working capacitors are connected in parallel;
The rated voltage must be at least 300 Volts;
The capacity of the working capacitors is selected taking into account 7 µF per 100 W;
It is desirable that the type of working and starting capacitor be identical. Popular options are MBGP, MPGO, KBP and others.

If you take these rules into account, you can extend the life of the capacitors and the electric motor as a whole.

Capacity calculations must be made taking into account the rated power of the electric motor. If the motor is underloaded, overheating is inevitable, and then the capacity of the working capacitor will have to be reduced.

If you choose a capacitor with a capacitance less than acceptable, the efficiency of the electric motor will be low.

Remember that even after the circuit is turned off, the voltage remains on the capacitors, so it is worth discharging the device before starting work.

Also note that connecting an electric motor with a power of 3 kW or more to conventional wiring is prohibited, as this can lead to the machines turning off or the plugs burning out. In addition, there is a high risk of insulation melting.

To connect ED 380 to 220V using capacitors, proceed as follows:

Connect the containers to each other (as mentioned above, the connection should be parallel).
Connect the parts with two wires to the electric motor and a single-phase alternating voltage source.
Turn on the engine. This is done in order to check the direction of rotation of the device. If the rotor moves in the desired direction, no additional manipulations are necessary. Otherwise, the wires connected to the winding should be swapped.

With a capacitor, an additional simplified one is for a star circuit.

With a capacitor, an additional simplified one is for a triangle circuit.

How to connect with reverse

There are situations in life when you need to change the direction of rotation of the motor. This is also possible for three-phase electric motors used in a household network with one phase and zero.

To solve the problem, it is necessary to connect one terminal of the capacitor to a separate winding without the possibility of breaking, and the second - with the possibility of transferring from the “zero” to the “phase” winding.

To implement the circuit, you can use a switch with two positions.

The wires from “zero” and “phase” are soldered to the outer terminals, and the wire from the capacitor is soldered to the central terminal.

How to connect in a star-delta connection (with three wires)

For the most part, domestically produced EDs already have a star circuit assembled. All that is required is to reassemble the triangle.

The main advantage of the star/delta connection is the fact that the engine produces maximum power.

Despite this, such a scheme is rarely used in production due to the complexity of implementation.

To connect the motor and make the circuit operational, three starters are required.

The current is connected to the first (K1), and the stator winding is connected to the other. The remaining ends are connected to starters K3 and K2.

When the K3 starter is connected to the phase, the remaining ends are shortened and the circuit is converted into a “star”.

Please note that simultaneous activation of K2 and K3 is prohibited due to the risk of a short circuit or knocking out of the AV supplying the ED.

To avoid problems, a special interlock is provided, which means turning off one starter when turning on the other.

The operating principle of the circuit is simple:

When the first starter is connected to the network, the time relay starts and supplies voltage to the third starter.
The engine starts working in a star configuration and starts working with more power.
After some time, the relay opens contacts K3 and connects K2. In this case, the electric motor operates in a “triangle” pattern with reduced power. When it is necessary to turn off the power, K1 turns on.

As can be seen from the article, it is possible to connect a three-phase electric motor to a single-phase network without loss of power.

At the same time, for home use, the simplest and most affordable option is using a starting capacitor.

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How to start a three-phase motor from 220 volts

As a rule, to connect a three-phase electric motor, three wires and a supply voltage of 380 volts are used. There are only two wires in a 220 volt network, so in order for the engine to work, voltage must also be applied to the third wire. For this purpose, a capacitor is used, which is called a working capacitor.

The capacitor capacity depends on the engine power and is calculated by the formula:
C=66*P, where C is the capacitance of the capacitor, μF, P is the power of the electric motor, kW.

That is, for every 100 W of engine power it is necessary to select about 7 µF of capacitance. Thus, a 500 watt motor requires a capacitor with a capacity of 35 µF.

The required capacity can be assembled from several capacitors of smaller capacity by connecting them in parallel. Then the total capacity is calculated using the formula:
Ctotal = C1+C2+C3+…..+Cn

It is important to remember that the operating voltage of the capacitor should be 1.5 times the power supply to the electric motor. Therefore, with a supply voltage of 220 volts, the capacitor should be 400 volts. Capacitors can be used of the following types: KBG, MBGCh, BGT.

To connect the motor, two connection schemes are used - “triangle” and “star”.

If in a three-phase network the motor was connected according to a delta circuit, then we connect it to a single-phase network according to the same circuit with the addition of a capacitor.

The star connection of the motor is carried out according to the following diagram.

To operate electric motors with a power of up to 1.5 kW, the capacity of the working capacitor is sufficient. If you connect a higher power engine, then such an engine will accelerate very slowly. Therefore it is necessary to use a starting capacitor. It is connected in parallel with the run capacitor and is used only during engine acceleration. Then the capacitor is turned off. The capacitor capacity to start the engine should be 2-3 times greater than the operating capacity.

After starting the engine, determine the direction of rotation. Typically you want the motor to rotate clockwise. If the rotation occurs in the desired direction, you do not need to do anything. To change direction, it is necessary to remount the engine. Disconnect any two wires, swap them and reconnect. The direction of rotation will change to the opposite.

When performing electrical installation work, follow safety regulations and use personal protective equipment against electric shock.

How to connect a three-phase motor to a 220 volt network

Connecting a 3-phase 220 motor with a capacitor
Video

Many owners, especially owners of private houses or cottages, use equipment with 380 V motors operating from a three-phase network. If an appropriate power supply circuit is connected to the site, then no difficulties arise with their connection. However, quite often a situation arises when a section is powered by only one phase, that is, only two wires are connected - phase and neutral. In such cases, you have to decide how to connect a three-phase motor to a 220 volt network. It can be done in various ways, however, it should be remembered that such intervention and attempts to change parameters will lead to a drop in power and a decrease in the overall efficiency of the electric motor.

Connecting a 3-phase 220 motor without capacitors

As a rule, circuits without capacitors are used to start low-power three-phase motors in a single-phase network - from 0.5 to 2.2 kilowatts. Start-up time is spent approximately the same as when operating in three-phase mode.

These circuits use triacs. under the control of pulses with different polarities. There are also symmetrical dinistors that supply control signals to the flow of all half-cycles present in the supply voltage.

There are two options for connecting and starting. The first option is used for electric motors with a speed of less than 1500 per minute. The windings are connected in a triangle. A special chain is used as a phase-shifting device. By changing the resistance, a voltage is generated across the capacitor, shifted by a certain angle relative to the main voltage. When the capacitor reaches the voltage level required for switching, the dinistor and triac are triggered, causing activation of the power bidirectional switch.

The second option is used when starting engines whose rotation speed is 3000 rpm. This category also includes devices installed on mechanisms that require a large moment of resistance during startup. In this case, it is necessary to provide a large starting torque. To this end, changes were made to the previous circuit, and the capacitors required for the phase shift were replaced by two electronic switches. The first switch is connected in series with the phase winding, leading to an inductive shift of the current in it. The connection of the second switch is parallel to the phase winding, which contributes to the formation of a leading capacitive current shift in it.

This connection diagram takes into account the motor windings, which are displaced in space by 120 0 C. When setting, the optimal angle of current shift in the phase windings is determined, ensuring reliable starting of the device. When performing this action, it is quite possible to do without any special equipment.

Connecting a 380V to 220V electric motor via a capacitor

For a normal connection, you should know the principle of operation of a three-phase motor. When connected to a three-phase network, current begins to flow alternately through its windings at different times. That is, in a certain period of time, the current passes through the poles of each phase, also creating a rotational magnetic field in turn. It exerts an influence on the rotor winding, causing rotation by pushing in different planes at certain times.

When such a motor is connected to a single-phase network, only one winding will participate in the creation of rotating torque and the impact on the rotor in this case occurs only in one plane. This force is completely insufficient to shift and rotate the rotor. Therefore, in order to shift the phase of the pole current, it is necessary to use phase-shifting capacitors. The normal operation of a three-phase electric motor largely depends on the right choice capacitor.

Calculation of a capacitor for a three-phase motor in a single-phase network:

With an electric motor power of no more than 1.5 kW, one operating capacitor will be sufficient in the circuit.
If the engine power is more than 1.5 kW or it experiences heavy loads during startup, in this case two capacitors are installed at once - a working one and a starting one. They are connected in parallel, and the starting capacitor is needed only for starting, after which it is automatically turned off.
The operation of the circuit is controlled by the START button and the power off toggle switch. To start the engine, press the start button and hold it until it is fully turned on.

If it is necessary to ensure rotation in different directions, an additional toggle switch is installed that switches the direction of rotation of the rotor. The first main output of the toggle switch is connected to the capacitor, the second to the neutral, and the third to the phase wire. If such a circuit causes a drop in power or a weak increase in speed, in this case it may be necessary to install an additional starting capacitor.

Connecting a 3-phase motor at 220 without loss of power

The simplest and in an efficient way It is considered to connect a three-phase motor to a single-phase network by connecting a third contact connected to a phase-shifting capacitor.

The highest output power that can be obtained in domestic conditions is up to 70% of the rated one. Such results are obtained when using the “triangle” scheme. Two contacts in the distribution box are directly connected to the wires of the single-phase network. The connection of the third contact is made through a working capacitor with any of the first two contacts or wires of the network.

In the absence of loads, a three-phase motor can be started using only a run capacitor. However, if there is even a small load, the speed will increase very slowly, or the engine will not start at all. In this case, an additional connection of a starting capacitor will be required. It turns on for literally 2-3 seconds so that the engine speed can reach 70% of the nominal speed. After this, the capacitor is immediately turned off and discharged.

Thus, when deciding how to connect a three-phase motor to a 220 volt network, all factors must be taken into account. Special attention should be given to capacitors, since the operation of the entire system depends on their action.

Attention, TODAY only!

Most asynchronous motors designed to operate in a three-phase 380 V network can be easily converted to work in the household, for example, for a grinding machine or drilling machine, where the network voltage is usually 220 V. In practice, the connection scheme to a single-phase network using capacitors is most often used.

It is worth noting that with such a connection, the power of the electric motor will be 50-60% of its rated power, but this will often be quite enough.

Not all three-phase electric motors work well when connected to a single-phase network. Problems arise, for example, with MA series engines with a double cage squirrel cage rotor. In this regard, when choosing three-phase electric motors for operation in a single-phase network, preference should be given to motors of the A, AO, AO2, APN, UAD, etc. series.

Why do we need capacitors? If you remember the theory, the windings in an asynchronous motor have a phase shift of 120 degrees, which creates a rotating magnetic field. The rotating magnetic field, crossing the rotor windings, induces an electromotive force in them, which leads to the appearance electromagnetic force, under the influence of which the rotor begins to rotate. But this is valid only for a three-phase network.

When connecting a three-phase motor to a single-phase network, the torque will be created by only one winding and this force will not be enough to rotate the rotor. To create a phase shift relative to the supply phase, phase-shifting capacitors are used.

The most common schemes for connecting a three-phase motor to a single-phase network are the "delta" circuit and the "star" circuit. When connected in a “triangle”, the output power of the electric motor will be greater than that of a “star”, so it is usually used in everyday life.

In order to determine which circuit the motor is connected to, you need to remove the terminal block cover and see how the jumpers are installed.

In the case of a triangle connection, all windings must be connected in series, that is, the end of one winding with the beginning of the next.

If only 3 pins are connected to the terminal block, then you will have to disassemble the motor and find a common connection point for the three ends of the windings. This connection must be broken, a separate wire must be soldered to each end, and then brought out to the terminal block. Thus, we will already get 6 wires, which we will connect in a “triangle” pattern.

Once you have decided on the connection diagram, you need to select the capacitance of the capacitors. The capacity of the working capacitor can be determined by the formula C slave = 66 R nom, Where R nom— rated engine power. That is, for every 100 W of power we take approximately 7 μF of the capacity of the working capacitor. If a capacitor of the required capacity is not available, you can select from several capacitors by connecting them in parallel. Capacitors can be used of any type, except electrolytic. Capacitors of the type MBGO, MBGP. The capacity of the starting capacitor should be approximately 2-3 times greater than the capacity of the working capacitor. The operating voltage of the capacitors should be 1.5 times the mains voltage.

If the engine begins to overheat after starting, the calculated capacitor capacity is overestimated. If the capacitor capacity is insufficient, a strong drop in motor power will occur. With the correct selection of capacitor capacitance, the current in the winding connected through the working capacitor will be the same or slightly different from the current consumed by the other two windings. It is recommended to select containers starting from the lowest permissible value, gradually increasing the capacity to the required value.

In the case of connecting low-power motors that initially operate without load, you can get by with one working capacitor.

Most often, our houses, plots, and garages are supplied with a single-phase 220 V network. Therefore, equipment and all home-made products are made so that they work from this power source. In this article we will look at how to correctly connect a single-phase motor.

Asynchronous or collector: how to distinguish

In general, you can distinguish the type of engine by the plate - the nameplate - on which its data and type are written. But this is only if it has not been repaired. After all, anything can be under the casing. So if you are not sure, it is better to determine the type yourself.

How do collector motors work?

You can distinguish between asynchronous and commutator motors by their structure. The collectors must have brushes. They are located near the collector. Another mandatory attribute of this type of engine is the presence of a copper drum, divided into sections.

Such motors are produced only single-phase; they are often installed in household appliances, since they allow you to get large number rpm at the start and after acceleration. They are also convenient because they easily allow you to change the direction of rotation - you just need to change the polarity. It is also easy to organize a change in the rotation speed by changing the amplitude of the supply voltage or its cutoff angle. That is why such engines are used in most household and construction equipment.

Disadvantages of commutator engines are high operating noise at high speeds. Remember a drill, an angle grinder, a vacuum cleaner, a washing machine, etc. The noise during their operation is decent. At low speeds, brushed motors are not so noisy ( washing machine), but not all tools work in this mode.

The second unpleasant point is that the presence of brushes and constant friction leads to the need for regular maintenance. If the current collector is not cleaned, contamination with graphite (from brushes being worn out) can cause adjacent sections in the drum to become connected and the motor simply stops working.

Asynchronous

An asynchronous motor has a starter and a rotor, and can be single or three phase. In this article we consider connecting single-phase motors, so we will only talk about them.

Asynchronous motors are characterized by a low noise level during operation, therefore they are installed in equipment whose operating noise is critical. These are air conditioners, split systems, refrigerators.

There are two types of single-phase asynchronous motors - bifilar (with a starting winding) and capacitor. The whole difference is that in bifilar single-phase motors the starting winding works only until the motor accelerates. Afterwards it is turned off by a special device - a centrifugal switch or a start-up relay (in refrigerators). This is necessary, since after overclocking it only reduces efficiency.

In capacitor single-phase motors, the capacitor winding runs all the time. Two windings - main and auxiliary - are shifted relative to each other by 90°. Thanks to this, you can change the direction of rotation. The capacitor on such engines is usually attached to the housing and is easy to identify by this feature.

You can more accurately determine the bifolar or capacitor motor in front of you by measuring the windings. If the resistance of the auxiliary winding is less than half (the difference can be even more significant), most likely this is a bifolar motor and this auxiliary winding is a starting winding, which means that a switch or starting relay must be present in the circuit. In capacitor motors, both windings are constantly in operation and connecting a single-phase motor is possible through a regular button, toggle switch, or automatic machine.

Connection diagrams for single-phase asynchronous motors

With starting winding

To connect a motor with a starting winding, you will need a button in which one of the contacts opens after switching on. These opening contacts will need to be connected to the starting winding. In stores there is such a button - this is PNDS. Its middle contact closes for the holding time, and the two outer ones remain in a closed state.

Appearance of the PNVS button and the state of the contacts after the “start” button is released.”

First, using measurements, we determine which winding is working and which is starting. Typically the output from the motor has three or four wires.

Consider the option with three wires. In this case, the two windings are already combined, that is, one of the wires is common. We take a tester and measure the resistance between all three pairs. The working one has the lowest resistance, the average value is the starting winding, and the highest is the common output (the resistance of two windings connected in series is measured).

If there are four pins, they ring in pairs. Find two pairs. The one with less resistance is the working one, the one with more resistance is the starting one. After this, we connect one wire from the starting and working windings, and bring out the common wire. A total of three wires remain (as in the first option):

one from the working winding is working;
from the starting winding;
general.

With all these

connecting a single-phase motor

We connect all three wires to the button. It also has three contacts. Be sure to place the starting wire on the middle contact(which is closed only during start-up), the other two are extremelyie (arbitrarily). We connect a power cable (from 220 V) to the extreme input contacts of the PNVS, connect the middle contact with a jumper to the working one ( pay attention! not with the general). That's the whole circuit for switching on a single-phase motor with a starting winding (bifolar) through a button.

Condenser

When connecting a single-phase capacitor motor, there are options: there are three connection diagrams and all with capacitors. Without them, the engine hums, but does not start (if you connect it according to the diagram described above).

The first circuit - with a capacitor in the power supply circuit of the starting winding - starts well, but during operation the power it produces is far from rated, but much lower. The connection circuit with a capacitor in the connection circuit of the working winding gives the opposite effect: not very good performance at start-up, but good performance. Accordingly, the first circuit is used in devices with heavy starting (for example), and with a working capacitor - if good performance characteristics are needed.

Circuit with two capacitors

There is a third option for connecting a single-phase motor (asynchronous) - install both capacitors. It turns out something between the options described above. This scheme is implemented most often. It is in the picture above in the middle or in the photo below in more detail. When organizing this circuit, you also need a PNVS type button, which will connect the capacitor only during the start time, until the motor “accelerates”. Then two windings will remain connected, with the auxiliary winding through a capacitor.

Connecting a single-phase motor: circuit with two capacitors - working and starting

When implementing other circuits - with one capacitor - you will need a regular button, machine or toggle switch. Everything connects there simply.

Selection of capacitors

There is a rather complex formula by which you can calculate the required capacity accurately, but it is quite possible to get by with recommendations that are derived from many experiments:

The working capacitor is taken at the rate of 70-80 uF per 1 kW of engine power;
starting - 2-3 times more.

The operating voltage of these capacitors should be 1.5 times higher than the network voltage, that is, for a 220 V network we take capacitors with an operating voltage of 330 V and higher. To make starting easier, look for a special capacitor in the starting circuit. They have the words Start or Starting in their markings, but you can also use regular ones.

Changing the direction of motor movement

If, after connecting, the motor works, but the shaft does not rotate in the direction you want, you can change this direction. This is done by changing the windings of the auxiliary winding. When assembling the circuit, one of the wires was fed to the button, the second was connected to the wire from the working winding and the common one was brought out. This is where you need to switch the conductors.

In various amateur electromechanical machines and devices, in most cases three-phase asynchronous motors with a squirrel cage rotor are used. Alas, a three-phase network in everyday life is a very rare phenomenon, therefore, to power them from an ordinary electrical network, amateurs use a phase-shifting capacitor, which does not allow the full power and starting properties of the motor to be realized.

Asynchronous three-phase electric motors, namely them, due to their widespread use, often have to be used, consist of a stationary stator and a movable rotor. Winding conductors are laid in the stator slots with an angular distance of 120 electrical degrees, the beginnings and ends of which (C1, C2, C3, C4, C5 and C6) are brought out into the junction box.

Delta connection (for 220 volts)

Star connection (for 380 volts)

Three-phase motor junction box with jumper positions for star connection

When a three-phase motor is turned on to a three-phase network, a current begins to flow through its windings at different times in turn, creating a rotating magnetic field that interacts with the rotor, forcing it to spin. When the motor is connected to a single-phase network, no torque capable of moving the rotor is created.

If you can connect the engine on the side to a three-phase network, then determining the power is not difficult. We place an ammeter at the break in one of the phases. Let's launch. We multiply the ammeter readings by the phase voltage.

In a good network it is 380. We get the power P=I*U. We subtract 10-12% for efficiency. You get the actually correct result.

There are mechanical instruments for measuring revolutions. Although it is also possible to determine by ear.

Among the various methods of connecting three-phase electric motors to a single-phase network, the most common is connecting the third contact through a phase-shifting capacitor.

Connecting a three-phase motor to a single-phase network

The rotational speed of a three-phase motor operating from a single-phase network remains almost the same as when it is connected to a three-phase network. Alas, this cannot be stated about power, the losses of which reach significant values. Clear values of power loss depend on the switching circuit, operating conditions of the motor, and the capacitance value of the phase-shifting capacitor. Approximately, a three-phase motor in a single-phase network loses within 30-50% of its own power.

Not many three-phase electric motors are ready to perform well in single-phase networks, but most of them cope with this task completely satisfactorily - except for the loss of power. Mainly, for operation in single-phase networks, asynchronous motors with a squirrel-cage rotor (A, AO2, AOL, APN, etc.) are used.

Asynchronous three-phase motors are designed for 2 rated network voltages - 220/127, 380/220, and so on. Electric motors with an operating voltage of windings of 380/220V (380V for star, 220 for delta) are more common. The highest voltage is for the "star", the lowest - for the "triangle". In the passport and on the motor plate, in addition to other characteristics, the operating voltage of the windings, their connection diagram and the likelihood of its change are indicated.

Three-phase motor labels

The designation on plate A states that the motor windings can be connected both as a “triangle” (at 220V) and a “star” (at 380V). When connecting a three-phase motor to a single-phase network, it is better to use a delta circuit, since in this case the motor will lose less power than when switched on as a star.

Plate B informs you that the motor windings are connected in a star configuration, and the junction box does not take into account the possibility of switching them to delta (there are no more than 3 terminals). In this case, all that remains is to either come to terms with a large loss of power by connecting the motor in a star configuration, or, having penetrated the electric motor winding, try to bring out the missing ends in order to connect the windings in a delta configuration.

If the operating voltage of the motor is 220/127V, then the motor can only be connected to a single-phase 220V network using a star circuit. When you turn on 220V in a delta circuit, the engine will burn out.

Beginnings and ends of windings (various options)

Probably the main difficulty in connecting a three-phase motor to a single-phase network is to understand the electrical wires going into the junction box or, in the absence of one, simply leading out of the motor.

The most common option is when the windings in an existing 380/220V motor are already connected in a delta circuit. In this case, you simply need to connect the current-carrying electrical wires and the working and starting capacitors to the motor terminals according to the connection diagram.

If the windings in the motor are connected by a “star”, and there is a possibility of changing it to a “triangle”, then this case also cannot be classified as labor-intensive. You just need to change the winding connection circuit to a “triangle” one, using jumpers for this.

Determination of the beginnings and ends of the windings. The situation is more difficult if 6 wires are brought out into the junction box without indicating their belonging to a specific winding and marking the beginnings and ends. In this case, it comes down to solving two problems (Although before doing this, you should try to search the Internet for some documentation for the electric motor. It may describe what electrical wires of different colors refer to.):

identifying pairs of wires related to one winding;

finding the beginning and end of the windings.

The first problem is solved by “ringing” all the wires with a tester (measuring resistance). When there is no device, it is possible to solve it using a light bulb from a flashlight and batteries, connecting the existing electrical wires into the circuit alternately with the light bulb. If the latter lights up, it means that the two ends being tested belong to the same winding. This method identifies 3 pairs of wires (A, B and C in the figure below) related to 3 windings.

Determination of pairs of wires belonging to one winding

The second task is to determine the beginnings and ends of the windings; here it will be somewhat more complicated and you will need a battery and a pointer voltmeter. Digital is not suitable for this task due to inertia. The procedure for determining the ends and beginnings of the windings is shown in diagrams 1 and 2.

Finding the beginning and end of the windings

A battery is connected to the ends of one winding (for example, A), and a pointer voltmeter is connected to the ends of the other (for example, B). Now, when you break the contact of wires A with the battery, the voltmeter needle will swing in some direction. Then you need to connect a voltmeter to winding C and do the same operation with breaking the battery contacts. If necessary, changing the polarity of winding C (switching ends C1 and C2) it is necessary to ensure that the voltmeter needle swings in the same direction as in the case of winding B. Winding A is checked in the same way - with a battery connected to the winding C or B.

Ultimately, all manipulations should result in the following: when the battery contacts break with any of the windings, an electric potential of the same polarity should appear on the other two (the device arrow swings in one direction). Now all that remains is to mark the conclusions of the 1st bundle as the beginning (A1, B1, C1), and the conclusions of the other as the ends (A2, B2, C2) and connect them along the desired scheme- “triangle” or “star” (when the motor voltage is 220/127V).

Extracting missing ends. Probably the most difficult option is when the engine has a fusion of windings in a “star” configuration, and there is no ability to switch it to a “delta” (no more than 3 electrical wires are brought into the distribution box - the beginning of windings C1, C2, C3).

In this case, to turn on the motor according to the "triangle" circuit, you need to bring the missing ends of the windings C4, C5, C6 into the box.

Schemes for connecting a three-phase motor to a single-phase network

Triangle connection. In the case of a home network, based on the belief of obtaining greater output power, single-phase connection of three-phase motors in a delta circuit is considered more suitable. With all this, their power can reach 70% of the nominal. 2 contacts in the junction box are connected directly to the electrical wires of a single-phase network (220V), and the 3rd - through the working capacitor Cp to any of the first 2 contacts or the electrical wires of the network.

Ensuring launch. It is possible to start a three-phase motor without a load using a working capacitor (more details below), but if the electric motor has some kind of load, it either will not start or will begin to gain speed extremely slowly. Then, for a quick start, you need an auxiliary starting capacitor Sp (calculation of the capacitor capacity is described below). The starting capacitors are turned on only for the duration of the engine startup (2-3 seconds, until the speed reaches approximately 70% of the nominal), then the starting capacitor must be disconnected and discharged.

It is convenient to start a three-phase motor using a special switch, one pair of contacts of which closes when the button is pressed. When it is released, some contacts open, while others remain on - until the "stop" button is pressed.

Switch for starting electric motors

Reverse. The direction of rotation of the motor depends on which contact ("phase") the third phase winding is connected to.

The direction of rotation can be controlled by connecting the latter, through a capacitor, to a two-position switch connected by its two contacts to the first and 2nd windings. Depending on the position of the switch, the engine will rotate in one direction or the other.

The figure below shows a circuit with a starting and running capacitor and a reverse button, which allows for comfortable control of a three-phase motor.

Connection diagram for a three-phase motor to a single-phase network, with reverse and a button for connecting a starting capacitor

Star connection. A similar diagram for connecting a three-phase motor to a network with a voltage of 220V is used for electric motors whose windings are designed for a voltage of 220/127V.

Capacitors. The required capacity of working capacitors for operating a three-phase motor in a single-phase network depends on the connection circuit of the motor windings and other characteristics. For a star connection, the capacitance is calculated using the formula:

Cp = 2800 I/U

For a triangle connection:

Cp = 4800 I/U

Where Cp is the capacitance of the working capacitor in microfarads, I is the current in A, U is the network voltage in V. The current is calculated by the formula:

I = P/(1.73 U n cosph)

Where P is the electric motor power kW; n - engine efficiency; cosф - power factor, 1.73 - coefficient that determines the correspondence between linear and phase currents. The efficiency and power factor are indicated in the passport and on the motor plate. Traditionally, their value is located in the spectrum of 0.8-0.9.

In practice, the capacitance value of the working capacitor when connected in a triangle can be calculated using the simplified formula C = 70 Pn, where Pn is the rated power of the electric motor in kW. According to this formula, for every 100 W of electric motor power, you need about 7 μF of working capacitor capacity.

The correct selection of capacitor capacity is checked by the results of engine operation. If its value is greater than required under these operating conditions, the engine will overheat. If the capacity is less than required, the power output of the motor will become very low. It makes sense to look for a capacitor for a three-phase motor, starting with a small capacitance and gradually increasing its value to a rational one. If possible, it is much better to choose a capacitance by measuring the current in the electrical wires connected to the network and to the working capacitor, for example, with a current clamp. The current value should be closer. Measurements should be made in the mode in which the engine will operate.

When determining the starting capacity, we first proceed from the requirements for creating the required starting torque. Do not confuse the starting capacitance with the capacitance of the starting capacitor. In the above diagrams, the starting capacitance is equal to the sum of the capacitances of the working (Cp) and starting (Sp) capacitors.

If, due to operating conditions, the electric motor starts without load, then the starting capacitance is traditionally assumed to be the same as the working capacitance, in other words, a starting capacitor is not needed. In this case, the connection diagram is simplified and cheaper. To simplify this and generally reduce the cost of the circuit, it is possible to organize the possibility of disconnecting the load, for example, by making it possible to quickly and comfortably change the position of the motor to drop the belt drive, or by making the belt drive a pressing roller, for example, like the belt clutch of walk-behind tractors.

Starting under load requires the presence of an additional tank (Sp) that is connected temporarily to start the engine. An increase in the switchable capacitance leads to an increase in the starting torque, and at a certain specific value, the torque reaches its maximum value. A further increase in capacitance leads to the opposite effect: the starting torque begins to decrease.

Based on the condition of starting the engine under a load closest to the rated load, the starting capacitance must be 2-3 times greater than the working capacitance, that is, if the capacity of the working capacitor is 80 µF, then the capacitance of the starting capacitor must be 80-160 µF, which will provide the starting capacitance (sum of the capacitance of the working and starting capacitors) 160-240 µF. Although, if the engine has a small load when starting, the capacitance of the starting capacitor may be less or may not exist at all.

Starting capacitors operate for a short time (only a few seconds during the entire connection period). This makes it possible to use cheaper starting electrolytic capacitors, specially designed for this purpose, when starting the engine.

Note that for a motor connected to a single-phase network through a capacitor, operating in the absence of a load, the winding fed through the capacitor carries a current 20-30% higher than the rated one. Therefore, if the engine is used in an underloaded mode, the capacity of the working capacitor should be minimized. But then, if the engine was started without a starting capacitor, the latter may be required.

It is much better to use not 1 large capacitor, but several much smaller ones, partly due to the ability to select a good capacitance, connecting additional ones or disconnecting unnecessary ones, the latter are used as starting ones. The required number of microfarads is obtained by connecting several capacitors in parallel, based on the fact that the total capacitance in a parallel connection is calculated using the formula:

Determination of the beginning and end of the phase windings of an asynchronous electric motor

How to connect a 380 to 220 asynchronous motor. Connecting an electric motor. Connection diagrams for single-phase asynchronous motors