How to choose capacitors for an electric motor. Capacitor for an electric motor: selection tips and rules for connecting a starting capacitor How many microfarads per 1 kW single-phase

To ensure reliable operation of the electric motor, starting capacitors are used.

The greatest load on the electric motor occurs at the moment of its start. It is in this situation that the starting capacitor begins to work. We also note that in many situations the start-up is carried out under load. In this case, the load on the windings and other components is very high. What design allows you to reduce the load?

All capacitors, including starting capacitors, have the following features:

As a dielectric special material is used. In this case, an oxide film is often used, which is applied to one of the electrodes.
Large capacity with small overall dimensions - a feature of polar storage devices.
Non-polar They are more expensive and larger, but they can be used without regard to polarity in the circuit.

This design is a combination of 2 conductors that are separated by a dielectric. The use of modern materials can significantly increase the capacity indicator and reduce its overall dimensions, as well as increase its reliability. Many with impressive performance indicators have dimensions of no more than 50 millimeters.

Purpose and benefits

Capacitors of the type in question are used in the connection system. In this case, it works only at the time of start-up, until the operating speed is reached.

The presence of such an element in the system determines the following:

Starting capacity makes it possible to bring the state of the electric field closer to circular.
Held significant increase in magnetic flux.
Rising starting torque, engine performance is significantly improved.

Without the presence of this element in the system, the service life of the engine is significantly reduced. This is due to the fact that a complex start-up leads to certain difficulties.

The AC mains can serve as a power source when using this type of capacitor. Almost all used versions are non-polar; they have a comparatively higher operating voltage for oxide capacitors.

The advantages of a network that has a similar element are as follows:

Easier engine starting.
Life time the engine is much larger.

The starting capacitor operates for several seconds when the engine starts.

Connection diagrams

wiring diagram for an electric motor with a starting capacitor

The circuit that has a starting capacitor in the network has become more widespread.

This scheme has certain nuances:

Start winding and capacitor turn on when the engine starts.
Additional winding works for a short time.
Thermal relay is included in the circuit to protect the additional winding from overheating.

If it is necessary to provide high torque during startup, a starting capacitor is included in the circuit, which is connected together with the working capacitor. It is worth noting that quite often its capacity is determined empirically to achieve the highest starting torque. Moreover, according to the measurements taken, the value of its capacity should be 2-3 times greater.

The main points of creating an electric motor power circuit include the following:

From the current source, 1 branch goes to the working capacitor. It works all the time, which is why it got its name.
There is a fork in front of him, which goes to the switch. In addition to the switch, another element can be used that starts the engine.
After the switch a starting capacitor is installed. It operates for a few seconds until the rotor picks up speed.
Both capacitors go to the engine.

You can make a connection in a similar way.

It is worth noting that the working capacitor is present in the circuit almost constantly. Therefore, it is worth remembering that they must be connected in parallel.

Selecting a starting capacitor for an electric motor

A modern approach to this issue involves the use of special calculators on the Internet that perform quick and accurate calculations.

To carry out the calculation, you should know and enter the following indicators:

Motor winding connection type: triangle or star. The capacitance also depends on the type of connection.
Engine power is one of the determining factors. This indicator is measured in Watts.
Mains voltage taken into account in calculations. As a rule, it can be 220 or 380 Volts.
Power factor– a constant value, which is often 0.9. However, it is possible to change this indicator during calculation.
Electric motor efficiency also affects the calculations performed. This information, as well as others, can be found by studying the information printed by the manufacturer. If it is not there, you should enter the engine model on the Internet to search for information about what the efficiency is. You can also enter an approximate value, which is typical for such models. It is worth remembering that efficiency may vary depending on the condition of the electric motor.

Such information is entered into the appropriate fields and an automatic calculation is carried out. At the same time, we obtain the capacity of the working condensate, and the starting condensate should have an indicator 2.5 times greater.

You can carry out such a calculation yourself.

To do this, you can use the following formulas:

For the star winding connection type, Capacitance is determined using the following formula: Cр=2800*I/U. In the case of a triangle connection of the windings, the formula Cр=4800*I/U is used. As you can see from the information above, the type of connection is the determining factor.
The above formulas determine the need to calculate the amount of current that passes through the system. For this, the formula is used: I=P/1.73Uηcosφ. For the calculation you will need engine performance indicators.
After calculating the current you can find the capacitance indicator of the working capacitor.
Launcher, as previously noted, should be 2 or 3 times higher in capacity than the worker.

When choosing, you should also consider the following nuances:

Interval operating temperature.
Possible deviation from the design capacity.
Insulation resistance.
Loss tangent.

Usually, the above parameters are not paid much attention. However, they can be taken into account to create an ideal electric motor power system.

Overall dimensions can also be a determining factor. In this case, the following dependence can be distinguished:

Capacity increase leads to an increase in the diametrical size and exit distance.
Most common maximum diameter 50 millimeters with a capacitance of 400 μF. At the same time, the height is 100 millimeters.

In addition, it is worth considering that on the market you can find models from foreign and domestic manufacturers. As a rule, foreign ones are more expensive, but also more reliable. Russian versions are also often used when creating an electric motor connection network.

Model overview

capacitor CBB-60

There are several popular models that can be found on sale.

It is worth noting that these models differ not in capacity, but in type of design:

Metallized polypropylene options execution of the SVV-60 brand. The cost of this version is about 300 rubles.
Film grades NTS are somewhat cheaper. With the same capacity, the cost is about 200 rubles.
E92– products from domestic manufacturers. Their cost is small - about 120-150 rubles for the same capacity.

There are other models, often differing in the type of dielectric used and the type of insulating material.

Often, the electric motor can operate without including a starting capacitor in the circuit.
Include this element in the circuit Only recommended if starting under load.
Also, greater engine power also requires the presence of similar elements in the circuit.
Special attention It is worth paying attention to the connection procedure, since violating the integrity of the structure will lead to its malfunction.

And most asynchronous motors are designed for 380 V and three phases. And when making homemade drilling machines, concrete mixers, emery machines and others, it becomes necessary to use a powerful drive. A motor from an angle grinder, for example, cannot be used - it has a lot of revolutions and little power, so you have to use mechanical gearboxes, which complicate the design.

Design features of asynchronous three-phase motors

Asynchronous AC machines are a godsend for any owner. It’s just that connecting them to a household network turns out to be problematic. But you can still find a suitable option, the use of which will result in minimal power losses.

Before you need to understand its design. It consists of the following elements:

The rotor is made according to the “squirrel cage” type.
Stator with three identical windings.
Terminal box.

There must be a metal nameplate on the engine - all the parameters are written on it, even the year of manufacture. The wires from the stator go into the terminal box. Using three jumpers, all wires are connected to each other. Now let's look at what motor connection diagrams exist.

Star connection

Each winding has a beginning and an end. Before you connect a 380 to 220 motor, you need to find out where the ends of the windings are. To make a star connection, it is enough to install jumpers so that all ends are closed. Three phases must be connected to the beginning of the windings. When starting the engine, it is advisable to use this particular circuit, since high currents are not induced during operation.

But it is unlikely that it will be possible to achieve high power, so hybrid circuits are used in practice. The motor is started with the windings turned on in a star configuration, and when it reaches a stable mode, it switches to a delta configuration.

Connection diagram for delta windings

The disadvantage of using such a circuit in a three-phase network is that large currents are induced in the windings and wires. This leads to damage to electrical equipment. But when working on a 220 V household network, no such problems are observed. And if you are thinking about how to connect a 380 to 220 V asynchronous motor, then the answer is obvious - only by using a delta circuit. In order to make a connection according to this scheme, you need to connect the beginning of each winding to the end of the previous one. Power must be connected to the vertices of the resulting triangle.

Connecting the motor using a frequency converter

This method is at the same time the simplest, most progressive and expensive. Although, if you need the functionality of an electric drive, you won't regret any money. The cost of the simplest frequency converter is about 6,000 rubles. But with its help it will not be difficult to connect a 380 V motor to 220 V. But you need to choose the right model. Firstly, you need to pay attention to which network the device is allowed to connect to. Secondly, pay attention to how many outputs it has.

For normal operation in domestic conditions, you need the frequency converter to be connected to a single-phase network. And the output should have three phases. It is recommended to carefully study the operating instructions so as not to make a mistake with the connection, otherwise the powerful transistors installed in the device may burn out.

Using capacitors

When using a motor with a power of up to 1500 W, you can install only one capacitor - a working one. To calculate its power, use the formula:

Serb=(2780*I)/U=66*P.

I - operating current, U - voltage, P - engine power.

To simplify the calculation, you can do it differently - for every 100 W of power, 7 μF of capacitance is needed. Therefore, for a 750W motor you need 52-55uF (you need to experiment a bit to get the right phase shift).

In the event that a capacitor of the required capacity is not available, you need to connect in parallel those that are available, using the following formula:

Comm=C1+C2+C3+...+Cn.

A starting capacitor is required when using motors whose power exceeds 1.5 kW. The starting capacitor works only in the first seconds of switching on to give a “push” to the rotor. It is turned on via a button parallel to the working one. In other words, it causes a stronger phase shift. This is the only way to connect a 380 to 220 motor through capacitors.

The essence of using a working capacitor is to obtain the third phase. The first two are zero and phase, which is already in the network. There should be no problems connecting the motor; the most important thing is to hide the capacitors away, preferably in a sealed, strong case. If the element fails, it may explode and harm others. The capacitor voltage must be at least 400 V.

Connection without capacitors

But you can connect a 380 to 220 motor without capacitors; you don’t even have to buy a frequency converter for this. All you have to do is rummage around in the garage and find a few main components:

Two transistors type KT315G. The cost on the radio market is about 50 kopecks. per piece, sometimes even less.
Two thyristors type KU202N.
Semiconductor diodes D231 and KD105B.

You will also need capacitors, resistors (fixed and one variable), and a zener diode. The entire structure is enclosed in a housing that can protect against electric shock. The elements used in the design must operate at voltages up to 300 V and currents up to 10 A.

It is possible to carry out both mounted and printed mounting. In the second case, you will need foil material and the ability to work with it. Please note that domestic thyristors of the KU202N type get very hot, especially if the drive power is over 0.75 kW. Therefore, install the elements on aluminum radiators; if necessary, use additional airflow.

Now you know how to independently connect a 380 motor to a 220 motor (into a household network). There is nothing complicated about this, there are many options, so you can choose the most suitable one for a specific purpose. But it’s better to spend money once and purchase it; it increases the number of drive functions many times over.

If there is a need to connect an asynchronous three-phase electric motor to a household network, you may encounter a problem - it seems completely impossible to do this. But if you know the basics of electrical engineering, you can connect a capacitor to start an electric motor in a single-phase network. But there are also capacitorless connection options; they are also worth considering when designing an installation with an electric motor.

Simple ways to connect an electric motor

The easiest way is to connect the motor using a frequency converter. There are models of these devices that convert single-phase voltage to three-phase. The advantage of this method is obvious - there is no power loss in the electric motor. But the cost of such a frequency converter is quite high - the cheapest copy will cost 5-7 thousand rubles.

There is another method that is used less frequently - the use of a three-phase asynchronous winding to convert voltage. In this case, the entire structure will be much larger and more massive. Therefore, it will be easier to calculate which capacitors are needed to start the electric motor and install them by connecting them according to the diagram. The main thing is not to lose power, since the operation of the mechanism will be much worse.

Features of the circuit with capacitors

The windings of all three-phase electric motors can be connected according to two schemes:

“Star” - in this case, the ends of all windings are connected at one point. And the beginnings of the windings are connected to the supply network.
“Triangle” - the beginning of the winding is connected to the end of the adjacent one. The result is that the connection points of the two windings are connected to the power supply.

The choice of circuit depends on what voltage the motor is supplied with. Typically, when connected to a 380 V AC network, the windings are connected in a “star”, and when operating under a voltage of 220 V - in a “delta”.

In the picture above:

a) star connection diagram;

b) triangle connection diagram.

Since a single-phase network clearly lacks one supply wire, it needs to be made artificially. For this purpose, capacitors are used that shift the phase by 120 degrees. These are working capacitors; they are not enough when starting electric motors with a power of over 1500 W. To start powerful engines, you will need to additionally include another container, which will facilitate work during the start.

Working capacitor capacity

In order to find out what capacitors are needed to start an electric motor when operating on a 220 V network, you need to use the following formulas:

When connected in a star configuration C (slave) = (2800 * I1) / U (network).
When connected in a "triangle" C (slave) = (4800 * I1) / U (network).

Current I1 can be measured independently using clamps. But you can also use this formula: I1 = P / (1.73 U (network) cosφ η).

The value of power P, supply voltage, power factor cosφ, efficiency η can be found on the tag, which is riveted on the motor housing.

A simplified version of calculating a working capacitor

If all these formulas seem a little complicated to you, you can use their simplified version: C (slave) = 66 * P (motor).

And if we simplify the calculation as much as possible, then for every 100 W of electric motor power a capacitance of about 7 μF is required. In other words, if you have a 0.75 kW motor, then you will need a run capacitor with a capacity of at least 52.5 uF. After selection, be sure to measure the current when the motor is running - its value should not exceed the permissible values.

Start capacitor

In the event that the motor is subject to heavy loads or its power exceeds 1500 W, a phase shift alone cannot be done. You will need to know what other capacitors are needed to start an electric motor of 2.2 kW and higher. The starter is connected in parallel with the worker, but only it is excluded from the circuit when the idle speed is reached.

Be sure to turn off the starting capacitors - otherwise phase imbalance and overheating of the electric motor occurs. The starting capacitor should be 2.5-3 times larger in capacity than the working capacitor. If you consider that a capacitance of 80 μF is required for normal operation of the motor, then to start you need to connect another block of capacitors of 240 μF. You can hardly find capacitors with such a capacitance on sale, so you need to make the connection:

When the capacitances are added in parallel, the operating voltage remains the same as indicated on the element.
In a series connection, the voltages are added, and the total capacitance will be equal to C (total) = (C1*C2*..*CX)/(C1+C2+..+CX).

It is advisable to install starting capacitors on electric motors whose power is over 1 kW. It is better to reduce the power rating a little to increase the degree of reliability.

What type of capacitors to use

Now you know how to select capacitors to start an electric motor when operating on a 220 V AC network. After calculating the capacitance, you can begin to select a specific type of element. It is recommended to use the same type of elements as working and starting ones. Paper capacitors perform well; their designations are as follows: MBGP, MPGO, MBGO, KBP. You can also use foreign elements that are installed in computer power supplies.

The operating voltage and capacitance must be indicated on the body of any capacitor. One drawback of paper cells is that they are large in size, so to operate a powerful engine you will need a rather large battery of cells. It is much better to use foreign capacitors, since they are smaller in size and have a larger capacity.

Using Electrolytic Capacitors

You can even use electrolytic capacitors, but they have a peculiarity - they must operate on direct current. Therefore, to install them in the structure, you will need to use semiconductor diodes. It is undesirable to use electrolytic capacitors without them - they tend to explode.

But even if you install diodes and resistors, this cannot guarantee complete safety. If the semiconductor breaks through, then alternating current will flow to the capacitors, resulting in an explosion. The modern element base allows the use of high-quality products, for example, polypropylene capacitors for operation on alternating current with the designation SVV.

For example, the designation of elements SVV60 indicates that the capacitor is designed in a cylindrical housing. But SVV61 has a rectangular body. These elements operate under a voltage of 400... 450 V. Therefore, they can be used without problems in the design of any device that requires connecting an asynchronous three-phase electric motor to a household network.

Operating voltage

One important parameter of capacitors must be taken into account - operating voltage. If you use capacitors to start an electric motor with a very large voltage reserve, this will lead to an increase in the dimensions of the structure. But if you use elements designed to operate with a lower voltage (for example, 160 V), this will lead to rapid failure. In order for capacitors to function normally, their operating voltage must be approximately 1.15 times greater than the network voltage.

Moreover, one feature must be taken into account - if you use paper capacitors, then when working in alternating current circuits their voltage must be reduced by 2 times. In other words, if the housing indicates that the element is designed for a voltage of 300 V, then this characteristic is relevant for direct current. Such an element can be used in an alternating current circuit with a voltage of no more than 150 V. Therefore, it is better to assemble batteries from paper capacitors, the total voltage of which is about 600 V.

Connecting an electric motor: a practical example

Let's say you have an asynchronous electric motor designed to be connected to a three-phase AC network. Power - 0.4 kW, motor type - AOL 22-4. Main characteristics for connection:

Power - 0.4 kW.
Supply voltage - 220 V.
The current when operating from a three-phase network is 1.9 A.
The motor windings are connected using a star circuit.

Now it remains to calculate the capacitors to start the electric motor. The motor power is relatively small, therefore, to use it in a household network, you only need to select a working capacitor; there is no need for a starting capacitor. Using the formula, calculate the capacitance of the capacitor: C (slave) = 66*P (motor) = 66*0.4 = 26.4 µF.

You can use more complex formulas; the capacity value will differ slightly from this. But if there is no capacitor suitable for the capacitance, you need to connect several elements. When connected in parallel, the containers are folded.

note

Now you know which capacitors are best to use to start an electric motor. But the power will drop by about 20-30%. If a simple mechanism is set in motion, it will not be felt. The rotor speed will remain approximately the same as indicated in the passport. Please note that if the motor is designed to operate from a 220 and 380 V network, then it is connected to a household network only if the windings are connected in a triangle. Carefully study the tag; if it only has the designation of a “star” circuit, then in order to work in a single-phase network you will have to make changes to the design of the electric motor.

But the operating voltage of our household network is 220 V. And in order to connect an industrial three-phase motor to a regular consumer network, phase-shifting elements are used:

starting capacitor;
working capacitor.

Connection diagrams for an operating voltage of 380 V

Industrially produced asynchronous three-phase motors can be connected in two main ways:

star connection";
delta connection".

Electric motors are structurally made of a movable rotor and a housing into which a stationary stator is inserted (can be assembled directly in the housing or inserted there). The stator consists of 3 equal windings, wound in a special way and located on it.

In a star connection, the ends of all three motor windings are connected together, and three phases are supplied to their beginnings. When connecting windings in a triangle, the end of one is connected to the beginning of the next.

Engine operating principle

When an electric motor is operating, connected to a three-phase 380 V network, voltage is sequentially applied to each of its windings and a current flows through each of them, creating an alternating magnetic field that affects the rotor, movably mounted on bearings, which causes it to rotate. To start with this type of operation, no additional elements are needed.

If one of the three-phase asynchronous electric motors is connected to a single-phase 220 V network, then no torque will arise and the motor will not start. To run three-phase devices from a single-phase network, many different options have been invented.

One of the simplest and most common among them is the use of phase shift. For this purpose, various phase-shifting capacitors are used for electric motors, through which the third phase contact is connected.

In addition, there must be one more element. This is the starting capacitor. It is designed to start the engine itself and should only work at the moment of starting for about 2-3 seconds. If it is left on for a long time, the motor windings will quickly overheat and it will fail.

To implement this, you can use a special switch that has two pairs of switchable contacts. When the button is pressed, one pair is fixed until the next press of the Stop button, and the second will be closed only when the Start button is pressed. This prevents motor failure.

Connection diagrams for operating voltage 220 V

Due to the fact that there are two main options for connecting electric motor windings, there will also be two circuits for supplying a household network. Designations:

“P” – switch that performs the start;
“P” is a special switch designed to reverse the engine;
“Sp” and “Cr” are starting and running capacitors, respectively.

When connected to a 220 V network, three-phase electric motors have the opportunity to change the direction of rotation to the opposite. This can be done using the “P” toggle switch.

Attention! The direction of rotation can only be changed when the supply voltage is turned off and the electric motor is completely stopped, so as not to break it.

“Сп” and “Ср” (working and starting capacitors) can be calculated using a special formula: Ср=2800*I/U, where I is the current consumed, U is the rated voltage of the electric motor. After calculating Cp, you can select Sp. The capacity of the starting capacitors should be at least twice as large as that of the Average. For convenience and simplification of choice, the following values can be taken as a basis:

M = 0.4 kW Av = 40 μF, Sp = 80 μF;
M = 0.8 kW Av = 80 μF, Sp = 160 μF;
M = 1.1 kW Av = 100 μF, Sp = 200 μF;
M = 1.5 kW Av = 150 μF, Sp = 250 μF;
M = 2.2 kW Av = 230 μF, Sp = 300 μF.

Where M is the rated power of the electric motors used, Cp and Sp are working and starting capacitors.

When using asynchronous electric motors designed for an operating voltage of 380 V in the domestic sphere, by connecting them to a 220 V network, you lose about 50% of the rated power of the motors, but the rotor speed remains unchanged. Keep this in mind when choosing the power needed for the job.

Power losses can be reduced by using a “triangle” connection of the windings; in this case, the efficiency of the electric motor will remain somewhere at the level of 70%, which will be significantly higher than when connecting the windings “star”.

Therefore, if it is technically feasible to change the star connection to a delta connection in the junction box of the electric motor itself, then do it. After all, purchasing an “additional” 20% of power will be a good step and help in your work.

When choosing starting and operating capacitors, keep in mind that their rated voltage must be at least 1.5 times greater than the mains voltage. That is, for a 220 V network, it is advisable to use containers designed for a voltage of 400 - 500 V for startup and stable operation.

Motors with an operating voltage of 220/127 V can only be connected as a star. If you use another connection, you will simply burn it when starting up, and all that remains is to scrap it all.

If you cannot find a capacitor used for start-up and operation, then you can take several of them and connect them in parallel. The total capacity in this case is calculated as follows: Total = C1+C2+....+Sk, where k is the required number.

Sometimes, especially under heavy load, it overheats greatly. In this case, you can try to reduce the degree of heating by changing the capacitance Cp (working capacitor). It is gradually reduced, while checking the engine heating. Conversely, if the operating capacity is insufficient, then the output power produced by the device will be small. In this case, you can try increasing the capacitor capacity.

For a faster and easier start-up of the device, if possible, disconnect the load from it. This applies specifically to those engines that have been converted from a 380 V network to a 220 V network.

Conclusion on the topic

If you want to use an industrial three-phase electric motor for your needs, then you need to assemble an additional connection diagram for it, taking into account all the conditions necessary for this. And be sure to remember that this is electrical equipment and you must comply with all safety standards and regulations when working with it.

Starting a 3-phase motor from 220 Volts

Often there is a need for subsidiary farming connect a three-phase electric motor, but there is only single-phase network(220 V). Nothing, the matter can be fixed. You just have to connect a capacitor to the motor and it will work.

The capacity of the capacitor used depends on the power of the electric motor and is calculated by the formula

C = 66 R nom,

Where WITH- capacitor capacity, μF, R nom - rated power of the electric motor, kW.

For example, a 600 W electric motor requires a capacitor with a capacity of 42 μF. A capacitor of such a capacity can be assembled from several parallel-connected capacitors of smaller capacity:

Ctot = C 1 + C 1 + … + C n

So, the total capacitance of the capacitors for a 600 W motor must be at least 42 μF. It must be remembered that capacitors are suitable whose operating voltage is 1.5 times the voltage in a single-phase network.

Capacitors of the KBG, MBGCh, and BGT types can be used as working capacitors. In the absence of such capacitors, electrolytic capacitors are also used. In this case, the housings of the electrolytic capacitors are connected to each other and are well insulated.

Note that the rotational speed of a three-phase electric motor operating from a single-phase network almost does not change compared to the rotational speed of the motor in three-phase mode.

Most three-phase electric motors are connected to a single-phase network in a delta circuit ( rice. 1). The power developed by a three-phase electric motor connected in a delta circuit is 70-75% of its rated power.

Fig 1. Schematic (a) and installation (b) diagrams for connecting a three-phase electric motor to a single-phase network according to the “delta” diagram

A three-phase electric motor is also connected according to the “star” circuit (Fig. 2).

Rice. 2. Schematic (a) and installation (b) diagrams for connecting a three-phase electric motor to a single-phase network according to the “star” circuit

To make a star connection, you need to connect two phase windings of the electric motor directly to a single-phase network (220 V), and the third through a working capacitor ( WITH p) to any of the two wires of the network.

To start a three-phase electric motor of small power, usually only a running capacitor is sufficient, but with a power greater than 1.5 kW, the electric motor either does not start or picks up speed very slowly, so it is also necessary to use a starting capacitor ( WITH P). The capacity of the starting capacitor is 2.5-3 times greater than the capacity of the working capacitor. Electrolytic capacitors of the type are best used as starting capacitors EP or the same type as working capacitors.

Connection diagram for a three-phase electric motor with a starting capacitor WITH n shown in rice. 3.

Rice. 3. Connection diagram of a three-phase electric motor to a single-phase network according to the “triangle” circuit with a starting capacitor C p

You need to remember: starting capacitors are turned on only for the duration of starting a three-phase motor connected to a single-phase network for 2-3 s, and then the starting capacitor is turned off and discharged.

Typically, the terminals of the stator windings of electric motors are marked with metal or cardboard tags indicating the beginnings and ends of the windings. If for some reason there are no tags, proceed as follows. First, the belonging of the wires to the individual phases of the stator winding is determined. To do this, take any of the 6 external terminals of the electric motor and connect it to any power source, and connect the second terminal of the source to the control light and, with the second wire from the lamp, touch the remaining 5 terminals of the stator winding in turn until the light comes on. When the light comes on, it means that the 2 terminals belong to the same phase. Conventionally, let's mark the beginning of the first wire C1 with tags, and its end - C4. Similarly, we will find the beginning and end of the second winding and designate them C2 and C5, and the beginning and end of the third - SZ and C6.

The next and main stage will be determination of the beginning and end of the stator windings. To do this, we will use the selection method, which is used for electric motors with a power of up to 5 kW. Let's connect all the beginnings of the phase windings of the electric motor according to the previously connected tags to one point (using a star circuit) and connect the motor to a single-phase network using capacitors.

If the engine immediately picks up the rated speed without a strong hum, this means that all the beginnings or all ends of the winding have hit the common point. If, when turned on, the engine hums strongly and the rotor cannot reach the rated speed, then in the first winding, swap terminals C1 and C4. If this does not help, return the ends of the first winding to their original position and now swap terminals C2 and C5. Do the same for the third pair if the engine continues to hum.

When determining the beginnings and ends of the phase windings of the stator of an electric motor, strictly adhere to safety regulations. In particular, when touching the stator winding clamps, hold the wires only by the insulated part. This must also be done because the electric motor has a common steel magnetic core and a large voltage may appear at the terminals of other windings.

For change direction of rotation the rotor of a three-phase electric motor connected to a single-phase network in a delta circuit (see. rice. 1), a third phase stator winding ( W) connect through a capacitor to the terminal of the second phase winding of the stator ( V).

To change the direction of rotation of a three-phase electric motor connected to a single-phase network in a star configuration (see. rice. 2, b), you need a third phase stator winding ( W) connect through a capacitor to the terminal of the second winding ( V). The direction of rotation of a single-phase motor is changed by changing the connection of the ends of the starting winding P1 And P2 (Fig. 4).

When checking the technical condition With electric motors, you can often notice with disappointment that after prolonged operation, extraneous noise and vibration appear, and the rotor is difficult to turn manually. The reason for this may be the poor condition of the bearings: the treadmills are covered with rust, deep scratches and dents, individual balls and the cage are damaged. In all cases, it is necessary to inspect the electric motor in detail and eliminate any existing faults. In case of minor damage, it is enough to wash the bearings with gasoline, lubricate them, and clean the engine housing from dirt and dust.

To replace damaged bearings, remove them with a screw puller from the shaft and wash the bearing seat with gasoline. Heat the new bearing in an oil bath to 80° C. Press a metal pipe, the inner diameter of which is slightly larger than the diameter of the shaft, into the inner ring of the bearing and lightly hit the pipe with a hammer and press the bearing onto the electric motor shaft. After this, fill the bearing 2/3 full with grease. Reassemble in reverse order. In a properly assembled electric motor, the rotor should rotate without knocking or vibration.

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