Wiring diagrams for connecting a three-phase motor to a single-phase network: capacitor, resistor, through a converter

In a personal household, it is often required to connect some kind of machine or device to facilitate activities. It can be a feed cutter, and a home-made crusher, and a circular, and a concrete mixer, and much more. All devices usually use asynchronous 3 phase motors. They are the most common. It remains only to choose the method of turning on this motor into a single-phase 220 V.

Standard connection

All three-phase asynchronous motors are connected to a 380 V. At the same time, they issue maximum power and the highest turnover. But not every owner has the opportunity to conduct all three phases to his site. This is due to the financial costs of installing special meters and various electricity metering boards. In addition, the paperwork itself takes quite a lot of time.

According to the standard scheme, to connect a three-phase motor to 380 V, three phases are connected

with standard motor terminals through the starters with which the launch is carried out. In the engine junction box, three contacts are usually free, to which three phases are attached. There is absolutely no difference which phase is connected to a specific wire. True, there is one nuance - when changing the connection wires, without touching the third wire, the electric motor rotates in the other direction, which is sometimes necessary in economic activity.

Connection of windings

Connection diagrams only two windings in the motor - "star" or "triangle". And how they are connected depends on the performance of the motor. No power is wasted with any connection. On the other hand, under excessive load, engines with a "star" slow down their speed than their counterparts with a "triangle". Hence, it is concluded that motors with a "star" require less starting current and, therefore, less load on the power grid when starting.

Motors with “delta” winding connection deliver their power to the end, even under heavy load, without losing speed at all. But then they suddenly stop, and for their next start, a huge starting current is required, which excessively overloads the electrical network.

In the industry, both connection schemes are used. Motors with a "star" are used where their systematic switching on and off is required, for example, on any lines of production, processing, assembly, and so on. Motors with windings connected in a "triangle" are needed for operation on permanent modes loads, for example, an unloading conveyor from a mine and others.

In personal subsidiary farms, motors are most often used, in which the connection of the windings is made according to the "star" principle. According to this scheme, the engines start easily, and this does not load the electrical network of a private house.

Electric motor in the home network

The usual nominal voltage of a home outlet is 220 V. It is considered single-phase, and all electrical devices are designed for it. Appliancesfrom the TV to the latest grinder.

But if it is necessary to connect a three-phase motor to a single-phase network, several problems arise. Namely:

• launching is impossible without additional devices;
• when the engine is running, 30 - 40% of the power is lost. This is a forced loss, since only two stator windings are involved in the work instead of three.

Still, asynchronous three-phase motors with a power of up to 2.2 kW are successfully connected to an ordinary household outlet. There are three proven ways to do this.

1. Capacitor connection of the electric motor.
2. Resistor switching.
3. Inclusion through a frequency converter.

All three connection methods have their pros and cons, so they choose the most convenient one for specific conditions. And also everything depends on the financial capabilities of the owner.

Capacitor connection

This is the most common way. And it consists in the introduction of a certain number of containers in order to there was a phase shift the third unused stator winding. This makes starting the motor much easier. How to connect a 220 volt 3-phase motor can be seen in detail in the diagram. Two types of stator winding connections are immediately presented here.

• C1-C4, C2-C5, C3-C6 - designations of stator windings;
• Ср - working capacitor;
• Cn - starting capacitor;
• KN - button to start.

Of course, if the motor without the use of capacitors is properly rotated by hand to 1 thousand. rpm, and then plug it into a 220 V network, then, most likely, it will work. But no one has ever done this. Usually searched or bought containers for starting.

The capacity of the working capacitor is calculated by the formula C = 67 × P, where P is the engine power in kW, and C is the capacitance of the capacitor in μF. In practice, they use an even simpler formula - 7 μF for every 100 W of power. For example, a 2.2 kW motor requires a 154 μF capacitor. Capacitors of such large capacities are quite rare, so they are recruited several and connected in parallel. In this case, it is necessary to take into account the voltage for which they are designed. It should be more than 220 volts by about one and a half times.

Typically, capacitors of such types as BGT, KBP, MBGCH, MBGO and the like are used. This is the most safe paper containerscapable of withstanding significant overload when starting the engine. In addition, they are weakly susceptible to heating. But in the absence of them, electrolytic capacitors are also used. In this case, the bodies of these containers are connected and well insulated, since after the electrolyte has dried out, they are capable of exploding under load. True, quite rarely.

When starting an engine with a power of up to 2.2 kW, only a working capacitor is used. It is quite enough to accelerate the engine to the nominal speed. With a higher power, it is necessary to use a starting capacitor. Its capacity is 2.5 - 3 times larger than the working one, that is, for a 2.2 kW motor it will be 300 - 450 μF. Electrolytic ones are often used as starting capacities, since in this case they work for a short time and are needed only for starting. After the motor sets its full speed, the starting capacitors are turned off with the KN button, which is shown in the diagram.

To change the direction of rotation of the electric motor, it is necessary to make changes. To do this, you need to refer to the diagram, where the windings are connected by a "star":

• instead of C1-C2, connect to a single-phase network C1-C3;
• the working capacitor Cp is connected between C2 and C3;
• switch the button with the starting capacitor to C2-C3.

In the "triangle" connection diagram, similar actions are carried out.

There is a special electrical circuit for switching motor rotation, which is rarely used in practice. Usually the rotation is set to one direction. A motor is needed to drive a specific device or unit, and to change the rotation of the working body, an ordinary gearbox is used. This can be seen in the example of a lathe or other machine. In personal subsidiary plots, for example, to change the course of the belt, where potatoes are calibrated, they also use a reducer. This greatly simplifies a certain task and provides good safety techniques.

Resistor switching of the electric motor

In the absence of capacitors to connect a three-phase motor to a single-phase network, sometimes use resistors. These are powerful ceramic or vitrified resistances. Tungsten wire up to 1 mm thick will do just fine. When connected, it is twisted into a spring and placed in a ceramic tube.

The size of the resistance is calculated by the formula R = (0.87 × U) / I, where U is the voltage of a single-phase network of 220 V, and I is the current value in amperes A.

The connection diagram with resistors is used only for motors with a power of up to 1 kW, since there is a large energy loss in the resistance.

Via frequency converter

Starting a 3-phase motor from a 220 V network using this device is now the most promising. This is why it is used in the latest electric drive control projects. The fact is that when the voltage and frequency of the network change, the number of motor revolutions changes, and as a result, the direction of rotation.

The converter is two electronic partswhich are in the same building. This is a control module and a power one. The first is directly responsible for starting and adjusting, and the second supplies the motor with electricity.

Using a converter to start a three-phase motor from a home network allows reduce the starting current dramatically and therefore the load. In practice, the motor can be started gradually, increasing its speed from 0 to 1000 - 1500 rpm.

While such a device has a very high cost, that limits its use in the household. In addition, due to the poor quality indicators of the power grid itself, the device is constantly being improved. This forces many owners to use the old proven methods of connecting three-phase motors to a single-phase network.

The use of single-phase motors in everyday life

In addition to three-phase motors, single-phase asynchronous motors are also widely used. They are used everywhere in powerful pumps, in washing machines, in heating and ventilation systems, and are also popular with private entrepreneurs who have decided to open their own sawmill.

Such motors are connected to a regular 220 V network. There are two windings inside these motors - one of them is starting and the other is working. When you create a phase shift between them, a rotating magnetic field is obtained - this is the main condition for starting these motors. The phases are shifted, as is the case with three-phase motors, by adding capacitors. The wiring diagram for a single-phase motor is very similar to that for a three-phase motor.

The calculation of capacitors is carried out according to the same formula or it is taken into account that for each kilowatt of motor power, 75 μF of capacity is needed. This is for a working capacitor, and for a starting capacitor - three times more. In addition, capacitors must be able to withstand a voltage of at least 300 V. At low engine power, they are quite costly with one working capacity.