Capacitors starting electrical characteristics. Capacitors for asynchronous motors. Connection diagram for a three-phase motor via a capacitor

Each object is initially supplied with three-phase current. The main reason is the use in power plants of generators with three-phase windings, out of phase with each other by 120 degrees and generating three sinusoidal voltages. However, with further distribution of current, only one phase is supplied to the consumer, to which all existing electrical equipment is connected.

Sometimes there is a need to use non-standard devices, so you have to solve the problem of how to choose a capacitor for a three-phase motor. As a rule, it is necessary to calculate the capacity of a given element that ensures stable operation of the unit.

The principle of connecting a three-phase device to one phase

In all apartments and most private houses, all internal energy supply is carried out through single-phase networks. Under these conditions, it is sometimes necessary to perform . This operation is quite possible from a physical point of view, since individual phases differ from each other only by a time shift. Such a shift can be easily organized by including any reactive elements in the circuit - capacitive or inductive. It is they who perform the function of phase-shifting devices when working and starting elements are used.

It should be taken into account that the stator winding itself has inductance. In this regard, it is quite enough to connect a capacitor with a certain capacitance outside the engine. At the same time, the stator windings are connected in such a way that the first of them shifts the phase of the other winding in one direction, and in the third winding the capacitor performs the same procedure, only in the other direction. As a result, the required phases are formed in the amount of three, extracted from a single-phase supply wire.

Thus, the three-phase motor acts as a load for only one phase of the connected power supply. As a result, an imbalance is formed in the energy consumed, which negatively affects general work networks. Therefore, this mode is recommended to be used for a short time for low-power electric motors. Connecting the windings in single-phase network can be done .

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

When a three-phase electric motor is planned to be connected to a single-phase network, it is recommended to give preference to a delta connection. An information plate attached to the housing warns about this. In some cases there is a “Y” designation here, which means a star connection. It is recommended to reconnect the windings in a delta configuration to avoid large power losses.

The electric motor is connected to one of the phases of a single-phase network, and the other two phases are created artificially. To do this, use worker (Wed) and starting capacitor(Sp). At the very beginning of starting the engine, it is necessary high level starting current, which cannot be provided by the working capacitor alone. A starting or starting capacitor, connected in parallel with the working capacitor, comes to the rescue. With low engine power, their performance is equal. Specially produced starting capacitors are marked “Starting”.

These devices operate only during starting periods in order to accelerate the engine to required power. It is subsequently turned off using a push-button or double switch.

Types of starting capacitors

Small electric motors, the power of which does not exceed 200-400 watts, can operate without a starting device. For them, one working capacitor is quite enough. However, if there are significant loads at the start, additional starting capacitors are necessarily used. It is connected in parallel with the working capacitor and during the acceleration period is kept in the on position using a special button or relay.

To calculate the capacitance of the starting element, it is necessary to multiply the capacitance of the working capacitor by a factor equal to 2 or 2.5. During acceleration, the engine requires less and less capacity. In this regard, you should not keep the starting capacitor constantly on. High capacity at high speeds will lead to overheating and failure of the unit.

The standard capacitor design consists of two plates located opposite each other and separated by a dielectric layer. When choosing a particular element, it is necessary to take into account its parameters and technical characteristics.

All capacitors are presented in three main types:

Polar. Cannot operate electric motors connected to alternating current. A collapsing dielectric layer can lead to heating of the unit and subsequent short circuit.
Non-polar. Received the greatest distribution. They can operate in any connection options due to the identical interaction of the plates with the dielectric and the current source.
Electrolytic. In this case, the electrodes are a thin oxide film. They can reach a maximum possible capacity of up to 100 thousand uF, ideal for low-frequency motors.

Selecting a capacitor for a three-phase motor

Capacitors intended for a three-phase motor must have a fairly high capacity - from tens to hundreds of microfarads. Electrolytic capacitors are not suitable for these purposes because they require a unipolar connection. That is, specifically for these devices it will be necessary to create a rectifier with diodes and resistances.

Gradually, the electrolyte in such capacitors dries out, which leads to loss of capacity. In addition, during operation, these elements sometimes explode. If you still decide to use electrolytic devices, you must take these features into account.

Classic examples are the elements presented in the figure. The working capacitor is shown on the left, and the starting capacitor on the right.

The selection of a capacitor for a three-phase motor is carried out experimentally. The capacity of the working device is selected at the rate of 7 μF per 100 W of power. Therefore, 600 W will correspond to 42 µF. The starting capacitor is at least 2 times the operating capacitance. Thus 2 x 45 = 90 uF would be the most appropriate figure.

The choice is made gradually, based on the operation of the engine, since its real power directly depends on the capacity of the capacitors used. In addition, this can be done using a special table. If there is insufficient capacity, the engine will lose its power, and if there is excess capacity, overheating will occur from excessive current. If the capacitor is selected correctly, the engine will operate normally, without jerking or extraneous noise. We select the device more accurately through calculations performed using special formulas.

Capacity calculation

The capacitance of the capacitor for the electric motor is calculated based on the winding connection diagram - star or triangle.

In both cases, the general calculation formula is applied: C slave = k x I f /U network, to which all parameters have the following designations:

k - is a special coefficient. Its value is 2800 for the star circuit and 4800 for the delta circuit.
If - rated stator current indicated on the information plate. If it is impossible to read, measurements are taken using special measuring clamps.
Umains is the supply voltage of 220 volts.

By substituting all the necessary values, you can easily calculate what capacity the working capacitor will have (μF). During calculations, it is necessary to take into account the current supplied to the stator phase winding. It should not exceed the rated value, just as the load on a motor with a capacitor should not exceed 60-80% of the rated power indicated on the information plate.

How to connect starting and running capacitors

The figure shows simplest scheme connecting the starting and working elements. The first of them is installed at the top, and the second at the bottom. At the same time, an on and off button is connected to the engine. The most important thing is to carefully understand the wires so as not to mix up the ends.

This scheme allows you to perform a preliminary check with an inaccurate estimate. It is also used after the final selection of the most optimal value.

This selection is carried out experimentally using several capacitors of different capacities. When connected in parallel, their total power will increase. At this time, you need to monitor the operation of the engine. If the operation is stable and smooth, in this case you can buy a capacitor with a capacitance equal to the sum of the capacitances of the test elements.

What should I do if I need to connect the motor to a source designed for a different type of voltage (for example, a three-phase motor to a single-phase network)? Such a need may arise, in particular, if you need to connect the motor to any equipment (drilling or sanding machine, etc.). In this case, capacitors are used, which, however, can be different types. Accordingly, you need to have an idea of what capacity a capacitor is needed for an electric motor, and how to correctly calculate it.

What is a capacitor

The capacitor consists of two plates located opposite each other. A dielectric is placed between them. Its task is to remove polarization, i.e. charge of nearby conductors.

There are three types of capacitors:

Polar. It is not recommended to use them in systems connected to AC power, because Due to the destruction of the dielectric layer, the device heats up, causing a short circuit.
Non-polar. They work in any switching mode, because their plates interact equally with the dielectric and with the source.
Electrolytic (oxide). A thin oxide film acts as electrodes. They are considered an ideal option for low-frequency electric motors, because... have the highest possible capacity (up to 100,000 µF).

How to choose a capacitor for a three-phase electric motor

When wondering: how to choose a capacitor for a three-phase electric motor, you need to take into account a number of parameters.

To select the capacitance for the working capacitor, you need to apply the following calculation formula: Work = k*Iph / U network, where:

k – special coefficient equal to 4800 for a “triangle” connection and 2800 for a “star” connection;
Iph is the rated value of the stator current, this value is usually indicated on the electric motor itself, but if it is erased or illegible, then it is measured with special pliers;
U mains – mains supply voltage, i.e. 220 volt.

This way you will calculate the capacitance of the working capacitor in microfarads.

Another calculation option is to take into account the engine power value. 100 watts of power corresponds to approximately 7 µF of capacitor capacity. When making calculations, do not forget to monitor the value of the current supplied to the stator phase winding. It should not have a greater value than the nominal value.

In the case when the engine is started under load, i.e. its starting characteristics reach maximum values; a starting capacitor is added to the working capacitor. Its peculiarity is that it operates for approximately three seconds during the start-up period of the unit and turns off when the rotor reaches the rated speed level. The operating voltage of the starting capacitor should be one and a half times higher than the network voltage, and its capacity should be 2.5-3 times greater than the working capacitor. To create the required capacitance, you can connect capacitors either in series or in parallel.

How to choose a capacitor for a single-phase electric motor

Asynchronous motors, designed to operate in a single-phase network, are usually connected to 220 volts. However, if in a three-phase motor the connection torque is specified constructively (location of the windings, phase displacement of the three-phase network), then in a single-phase motor it is necessary to create a rotary displacement torque of the rotor, for which an additional starting winding is used at startup. Its current phase is shifted using a capacitor.

So, how to choose a capacitor for a single-phase electric motor?

Most often, the value of the total capacitance Srab + Drain (not a separate capacitor) is as follows: 1 µF for every 100 watts.

There are several operating modes for engines of this type:

Starting capacitor + additional winding (connected during startup). Capacitor capacity: 70 µF per 1 kW of engine power.
Working capacitor (capacity 23-35 μF) + additional winding, which is connected during the entire operating time.
Running capacitor + starting capacitor (connected in parallel).

If you are thinking: how to choose a capacitor for a 220V electric motor, you should proceed from the proportions given above. However, it is necessary to monitor the operation and heating of the engine after connecting it. For example, if the unit noticeably heats up in mode with a working capacitor, the capacitance of the latter should be reduced. In general, it is recommended to select capacitors with an operating voltage of 450 V or more.

How to choose a capacitor for an electric motor is a difficult question. To ensure efficient operation of the unit, it is necessary to carefully calculate all parameters and proceed from the specific conditions of its operation and load.

A conventional synchronous and asynchronous motor is powered from an alternating voltage network. There are also “unusual” engines, for example, powered from the vehicle’s on-board network or from special generators. The principle of their operation is the same, but the frequency of the supply voltage, as a rule, is noticeably higher than 50 Hz.

In an AC motor, the stator provides spatial movement magnetic field. Without this, the rotor will not be able to start rotating on its own.

The role of capacitors in an electric drive

If the supply voltage is single-phase, using a capacitor you can obtain a magnetic field movement in the stator. To do this, it needs an additional winding. It is connected via a capacitor. The size of its capacity is directly proportional to the starting torque. If you measure its value (ordinate axis) according to the increase in capacitance (abscissa axis), you will get a curve. From a certain value of the capacitance, the increment in torque will become smaller and smaller.

The capacitance value, starting from which the increment in torque noticeably decreases, will be optimal for starting this motor. But for an overclocked engine and its long-term operation, the starting capacitor is always too large in capacity. To maintain stable operation of the electric motor, a run capacitor is used. Its capacity is less than that of the starter. You can also choose the right operating capacitor experimentally.

How to determine the optimal capacity size

This will require several capacitors connected in parallel. Along the connections, an ammeter measures the current consumed by the electric motor. It will decrease as the total capacity increases. But from a certain value its current will begin to increase. The minimum value of the current corresponds to the optimal value of the capacitance of the working capacitor. For normal operation of the engine, two capacitors are used with the possibility of parallel connection with each other. The connection diagram containing the starting and running capacitor is shown below.

When starting, they are connected, forming the best capacity for accelerating the engine. Why use a separate starting capacitor of the same capacity if the installation turns out to be unreasonably cumbersome. Therefore, it is advantageous to use a container made up of two parts. Although it also includes a run capacitor, it becomes part of the virtual start capacitor at startup. And those that can be switched off are called starting capacitors.

Calculation of working capacity

Experimental determination of the capacitance of capacitors is the most accurate. However, these experiments take a lot of time and are quite labor-intensive. Therefore, in practice, estimation methods are mainly used. They will require the engine power value and coefficients. They correspond to the “star” (12.73) and “triangle” (24) schemes. The power value is necessary to calculate the current strength. To do this, its nameplate value is divided by 220 (the value of the current mains voltage). Power is taken in watts.

The resulting number is multiplied by the corresponding coefficient and gives the value of microfarads.

Selection of starting capacity

But the mentioned method determines the capacity of the working capacitor. If the engine is used in an electric drive, it may not start with it. An additional starting capacitor will be required. In order not to bother yourself with selection, you can start with a container of the same size. If the engine still does not start due to the load on the drive side, it is necessary to add in parallel.

After each connected instance, you need to apply voltage to the engine to check startup. After the engine starts, the last of the connected capacitors will complete the formation of the capacitance required for the engine in starting mode. If for any reason, after being connected to the electrical network, the capacitor is disconnected from it, it must be discharged.

To do this, use a resistor with a value of several kilo-ohms. First, before connecting, its leads must be bent so that their ends are at the same distance as the terminals. The resistor is taken by one of the terminals with pliers with insulated handles. By pressing the resistor leads to the terminals for a few seconds, the capacitor is discharged. After this, it is advisable to check with a multimeter-voltmeter how many volts there are on it. It is desirable that the voltage either resets to zero or remains less than 36 V.

Metal paper and film capacitors

The amount of 220 V AC voltage used for technical characteristics engines, corresponds effective value. But with it, the amplitude voltage value will be 310 V. It is to this level that the electric motor capacitor will be charged. Therefore, the rated voltage of the starting and operating capacitor is selected with a margin and is at least 350 volts. The most reliable varieties are metal-paper and metal-film capacitors.

But their sizes are large, and the capacity of one capacitor is not enough for most industrial engines. For example, for a 1 kW engine, only the working capacitance is equal to 109.1 µF. Consequently, the starting capacity will be more than 2 times larger. To select a capacitor of the required capacity, for example, for a 3 kW engine if there is already a selected instance for a power of 1 kilowatt, you can take it as a basis. In this case, one capacitor is replaced by three connected in parallel.

For the operation of the engine, it makes no difference which capacitors - one or three - are used when turned on. But it’s better to choose three. This option is economical, despite the larger number of connections. Overvoltage will only damage one of the three. And replacing it will cost less. One large capacitor, when replaced, will have a significantly higher price.

If you need an optimal size specimen, it is selected in the table according to the data provided.

Electrolytic capacitors

The metal film capacitors under consideration are stable, reliable and durable, subject to the right conditions operation, among which the most important parameter is voltage. But in the electrical network, as a result of switching consumers, as well as for other reasons, overvoltages are possible. If a breakdown of the insulation of the plates occurs, they become unsuitable for further work. But this does not happen often, and the main problem with using these models is the dimensions.

A more compact alternative may be electrolytic capacitors (so-called electrolytes). They have significant differences in their smaller size and structure. Therefore, they can replace several units of metal and paper with 1 electrolyte. But the properties of their structure limit their service life. Although there are positive side- self-healing after a breakdown. Long-term operation of electrolytes on alternating current impossible. It will heat up and eventually collapse, at least safety valve. And even the body.

To prevent such incidents, diodes must be connected. Connecting the starting capacitor with diodes is done as shown in the image below. But this does not mean that any of the electrolyte models with a voltage of 350 V or more can be used. The level of pulsations and their frequency are strictly regulated. If these parameters are exceeded, heating begins. The capacitor may fail. To start and operate engines, special electrolytes with diodes inside are made. Only such models should be used for engines.

In electrical engineering, there are often options when an electric motor is connected, assembled to start from a 380-volt network to a household network. Capacitance storage devices are used to start electric motors.

Capacitors may differ in type of design and purpose; not every capacitance storage device is used in the starting start of an electric motor in the 220 network. For these reasons, you need to understand how to calculate the starting capacitor, what type of starting storage device should be chosen, how they differ in the operation of an electric motor with 220 volt network. Let's look at what a capacitive storage device is.

Purpose

When the question is asked what a starting capacitor is, it is recommended to consider the principle of operation of a capacitance storage device and why capacitors are needed to start an electric motor. Its design uses the property of conductors - polarization, when conductors located close to one another are charged. To remove the charge, plates are used in the capacitor design, they are located opposite each other, and a dielectric is installed between them.

Modern manufacturers of capacitive storage devices offer “condenser” of different modifications, with different values, for different applications. The buyer only has to choose a drive for the circuit.

Electric motors use starting capacitors for electric motors that operate on 220 volts. A starting capacitor is needed to spin the shaft of an electric motor; it is often under load.

Capacitors in their design have the following features:

acts as a dielectric different material, in electrolytic products of the SVV brand - an oxide film, which is applied to one of the built-in electrodes;
polar containers are small in size, but capable of accumulating large capacity;
a non-polar condenser (circuit element), has large dimensions, but is included in the circuit without taking into account polarity, and is characterized by high cost.

In the system for starting an electric motor in a 220 network, a working capacitance storage device and a starting capacitor are used; the starting storage device operates only at the moment the electric motor starts, until the rotor reaches the required speed for operation. The starting element in the circuit determines the following factors:

The starting electric charge storage device brings the electric field at the moment of start closer to the circular field of the electric motor;
Makes it possible to significantly increase the magnetic flux parameters;
Increases starting torque, improves the operation of the electric motor.

When the standard procedure involves starting a three-phase motor from a household electrical network and its further operation, the presence of capacitance in the starting circuit extends the duration effective use motor, since there is often a calculated load on the shaft. Non-polar capacitors have a higher operating voltage.

Electric motor for 3 phases in a 220V power supply

Eat different types starting electric motors for industrial use in a 220 volt power supply network, but starting capacitors are more often used to start the electric motor. This method is based on connecting the third stator winding to the power circuit through a phase-shifting condenser.

Important! When using a 3-phase electric motor in a single-phase network, its power from the nominal parameters of operation in a 380-volt network is reduced to 60%. In addition, not every brand of electric motor operates satisfactorily on 220 volts - these are MA brand engines. It is recommended to use brands of electric motors to switch the operation of electric motors from a 380 to 220 volt network: APN, A, UAD and other engines.

To start an engine with a capacitor start, it is necessary that the storage capacity can vary depending on the engine speed, which is almost impossible to realize. For this reason, experts recommend controlling the electric motor in two stages: when the electric motor is started, two capacitance storage units are used in operation; upon reaching the operating speed of the engine, the starting storage unit is turned off, leaving only the working capacitor.

How to calculate capacitors

The correct use of switching is indicated in the passport data of the electric motor. If it shows that the engine can operate from a 380/220V power supply, then for 220V you need to use a capacitor for the electric motor and connect it according to the following diagram.

The circuit works as follows: turning on switch P1, we close its contacts P1.1, as well as P1.2. At this moment, you must immediately press the “Acceleration” button when the electric motor reaches required speed, she is released. Reverse, or reverse rotation of the electric motor, in this connection can be realized using switch SA1, but after the engine has completely stopped.

There is a distinction between the selection of capacitance storage Cp, when the windings of the electric motor are connected according to the ∆ - triangle circuit, calculated by the formula:

Calculation of capacitance storage Cp, when the windings of the electric motor are connected according to the Y - star circuit, calculated by the formula:

storage device (capacitors) working (Cp), measured (µF);
current, electric motor (I), is measured (A);
mains voltage (U), measured (V).

The current consumed by the electric motor is calculated by the formula:

According to the formula:

The engine power can be viewed in the passport data or on the nameplate attached to the electric motor housing (P), measured in watts (W);
Efficiency (coefficient useful action) – h;
electric motor power factor – cos j;
mains voltage (U), measured in volts (V).

Note! The starting capacitor must be selected two or 2.5 times higher than the working storage capacity, since they are calculated not based on the mains voltage, but 1.5 times higher than it. So, for a single-phase 220 volt network, it is recommended to use capacitive storage devices of the brand: MBGCH or MBGO, whose operating voltage is 500 volts. There will be no noticeable difference which of these capacitors you choose; they both have proven themselves well.

For short-term use, you can use electrolytic storage devices, brand K50-3 or KE, as starting capacitors, the operating voltage is more than 450 volts.

It should be noted that when electrolytic capacitance storage devices are used, it is recommended to connect them in series for reliability and use a diode shunt.

(With total) = C1 + C2/2.

In fact, it is easier to use tables for selecting capacitors based on motor power.

Important! When choosing “capacitors” for an electric motor, it is necessary to take into account that when idling, the capacitance storage device included in the winding passes electricity up to 30% above nominal. This must be taken into account based on the operating mode of the electric motor. When it often operates without load or with partial load, the capacitance (Cp) is selected with a lower rating, and when the engine is overloaded and stops, it must be started again.

Portable unit

In practice, a portable unit is often used to start three-phase electric motors of small power within 500 watts, without reverse conditions.

The portable unit works as follows:

by pressing the button (SB1), we supply power to the magnetic starter (KM1), the switch (SA1) is in the “closed” position;
the group of contacts of the magnetic starter (KM1.1 and KM1.2) at this moment connects the electric motor (M1) to electrical network voltage 220 volts;
at the same time, the next contact group of the magnetic starter (KM3.1) closes the button (SB1);
when the electric motor has reached the required number of revolutions using the button (SA1), turn off the starting capacitors (C1);
The electric motor is stopped by pressing the button (SB2).

A portable unit is also being implemented with automatic shutdown of the starting storage tank; for this it is necessary to enter into the circuit additional device, a relay that will replace the operation of the toggle switch (SA1). The difference in the use of the block and the connection diagram for one motor is that the block is easy to work with several motors.

Capacitor start

It should be noted that capacitor starting is also used to start a single-phase motor. The difference between this type of motor and three-phase electric motors is that they do not lose power, but since the starting torque is low, a starting capacitance storage is needed.

Electric motors of this type have two stator windings in their design; for their operation, the same starting circuit is used using a capacitor for a single-phase motor. In this case, the total storage capacity can be calculated from a simple proportion. If you don’t know how to choose a capacitor, every 0.1 kilowatt of engine power is 1 microfarad of capacitance.

Important! In this calculation, a simplified calculation of the starting capacity of a single-phase electric motor, the obtained result must be taken as the total capacity, which consists of the starting and operating capacity of the drives.

Experts have analyzed many options for connecting asynchronous electric motors that have a standard power supply from a 380 V network and can be switched to operate from a 220 V network, and made the following conclusions:

When a motor is connected to a 220 volt network, it loses 50% of its power. Recommendation - to reduce power loss, switch the windings from Y to ∆ connection. Such a switch will also reduce power, but not by 50%, but by 30% of the rated power of the electric motor;
When selecting capacitors for the main circuit (working or starting), it is necessary to take into account their operating voltage, which should be one and a half times higher than the mains voltage, preferably from 400 volts;
The circuit of the electric motor powered by 220/127 volts is different, it is necessary to include the Y “star” circuit, another type of connection ∆ “delta” will burn out the electric motor;
When it is not possible to find a starting and running capacitor to operate and start the engine, you can assemble a chain of parallel-connected capacitance storage devices. In this case: C total = the sum of all capacitances of the capacitors (C1+C2+C3...);
If the motor gets hot during operation, you can lower the parameters of the working condenser connected to the electric motor winding. In the event that the engine does not have enough power, it is necessary to experimentally increase the parameters of the working condenser and capacity.

For home purposes, you can use a three-phase electric motor, which is used in industry, but take into account the fact that there will be power losses. The following brands of capacitors are popular among modification enthusiasts:

SVV-60 is a metallized polypropylene container storage device, its cost is 300 rubles;
brand of capacitors NTS - film, which cost a little cheaper, 200 rubles;
capacitive storage devices E92 costing up to 150 rubles;
The use of metal-paper storage tanks of the MBGO brand is widespread.

There are cases when a starting capacitor is not required. This is possible when starting the electric motor without load. But if the electric motor has a high power of 3 kW or more, a capacitor is needed to start the engine.

Video

There are 2 types of single-phase asynchronous motors - bifilar (with a starting winding) and capacitor. Their difference is that in bifilar single-phase motors the starting winding operates 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 because after overclocking it reduces efficiency.

In capacitor single-phase motors, the capacitor winding runs all the time. Two windings - main and auxiliary, they 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.

Connection diagram for a single-phase motor via a capacitor

When connecting a single-phase capacitor motor, there are several options for connection diagrams. Without capacitors, the electric motor hums, but does not start.

1 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.
3, 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, and with a working capacitor - if good performance characteristics are needed.
Diagram 2 - connecting a single-phase motor - install both capacitors. It turns out something between the options described above. This scheme is used most often. She's in the second picture. 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.

Connection diagram for a three-phase motor via a capacitor

Here, the voltage of 220 volts is distributed into 2 series-connected windings, where each is designed for this voltage. Therefore, the power is lost almost twice, but such an engine can be used in many low-power devices.

The maximum power of a 380 V motor in a 220 V network can be achieved using a delta connection. In addition to minimal power losses, the engine speed also remains unchanged. Here, each winding is used for its own operating voltage, hence the power.

It is important to remember: three-phase electric motors have higher efficiency than single-phase 220 V motors. Therefore, if there is a 380 V input, be sure to connect to it - this will ensure more stable and economical operation of the devices. To start the motor, you will not need various starters and windings, because a rotating magnetic field appears in the stator immediately after connecting to a 380 V network.

Online calculation of motor capacitor capacity

There is a special formula that can be used to calculate the required capacity exactly, but it’s quite possible to get by online calculator or recommendations that are derived from many experiences:

The working capacitor is taken at the rate of 0.8 μF per 1 kW of engine power;
The launcher is selected 2-3 times more.

Capacitors must be non-polar, that is, not electrolytic. The operating voltage of these capacitors must be at least 1.5 times higher than the network voltage, that is, for a 220 V network we take capacitors with an operating voltage of 350 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.

Starting capacitors for motors

These capacitors can be selected using the method from smallest to largest. Having thus selected the average capacity, you can gradually add and monitor the operating mode of the engine so that it does not overheat and has enough power on the shaft. Also, the starting capacitor is selected by adding until it starts smoothly without delays.

During normal operation of three-phase asynchronous electric motors with capacitor start, connected to a single-phase network, it is assumed that the capacitance of the capacitor will change (decrease) with increasing shaft speed. At the moment of starting asynchronous motors (especially with a load on the shaft) in a 220 V network, an increased capacity of the phase-shifting capacitor is required.

Reversing the direction of movement of the engine

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. This operation can be performed by a two-position switch, the central contact of which is connected to the output from the capacitor, and to the two outer terminals from “phase” and “zero”.