How to connect an asynchronous three-phase motor to 220. How to connect a single-phase motor

It must be connected to a 220 V home network. Since the engine will not start, it is necessary to change some parts in it. You can easily do this yourself. Even though the efficiency will decrease somewhat, this approach can be justified.

Three-phase and single-phase motors

To figure out how to connect an electric motor from 380 to we will find out what 380 volt power means.

Three-phase motors have many advantages over household single-phase motors. Therefore, their application in industry is extensive. And the point is not only in power, but also in efficiency. They also contain starting windings and capacitors. This simplifies the design of the mechanism. For example, the starting protective relay of a refrigerator monitors how many windings are connected. But in a three-phase motor there is no need for this element.

This is achieved through three phases, during which an electromagnetic field rotates inside the stator.

Why 380 V?

When the field inside the stator rotates, the rotor also moves. The revolutions do not coincide with the fifty Hertz of the network due to the fact that there are more windings, the number of poles is different, and also slippage occurs for various reasons. These indicators are used to regulate the rotation of the motor shaft.

All three phases have a value of 220 V. However, the difference between any two of them at any time will be different from 220. This will result in 380 Volts. That is, the engine is used for operation, and there is a phase shift of one hundred and twenty degrees.

Because it is impossible to directly connect a 380 to 220 Volt electric motor, you have to use tricks. A capacitor is considered the simplest method. When the capacitance goes through a phase, the latter changes by ninety degrees. Although it does not reach one hundred and twenty, this is enough to start and operate a three-phase motor.

How to connect an electric motor from 380 to 220 V

To implement the task, it is necessary to understand how the windings are arranged. Usually the case is protected by a casing, and wiring is located under it. After removing it, you need to examine the contents. You can often find a wiring diagram here. To connect to the 380-220 network, star-shaped switching is used. The ends of the windings are located at a common point called neutral. The phases are supplied to the opposite side.

The "star" will have to be changed. To do this, the motor windings must be connected in a different shape - in the form of a triangle, combining them at the ends with each other.

How to connect an electric motor from 380 to 220: diagrams

The diagram might look like this:

• the mains voltage is applied to the third winding;
• then the voltage will pass to the first winding through the capacitor with a phase shift of ninety degrees;
• the voltage difference will affect the second winding.

It is clear that the phase shift will be ninety and forty-five degrees. Because of this, the rotation will not be uniform. In addition, the phase shape on the second winding will not be sinusoidal. Therefore, after connecting a three-phase electric motor to 220 volts, it will not be able to be implemented without power losses. Sometimes the shaft even gets stuck and stops spinning.

Working capacity

After gaining speed, the starting capacity will no longer be needed, since the resistance to movement will become insignificant. To discharge the capacitance, it is shortened by a resistance through which the current will no longer pass. To correctly select the working and starting capacitance, you must first take into account that the operating capacitor voltage must significantly exceed 220 Volts. The minimum should be 400 V. You also need to pay attention to the wires so that the currents are intended for a single-phase network.

If the working capacity is too small, the shaft will stick, so an initial acceleration is used for it.

Working capacity also depends on the following factors:

• The more powerful the motor, the larger the capacitor rating required. If the value is 250 W, then a few tens of microfarads will be enough. However, if the power is higher, then the nominal value can be considered in the hundreds. It is better to purchase film capacitors, because electric ones will have to be additionally modified (they are designed for direct, not alternating current, and without modifications they can explode).
• The higher the engine speed, the higher the rating required. If we take a 3000 rpm engine with a power of 2.2 kW, then it will need a battery of 200 to 250 uF. And this is of great importance.

This capacity also depends on the load.

Final stage

It is known that an electric motor of 380 V at 220 Volts will work better if the voltages are equal. To do this, the winding connected to the network does not need to be touched, but the potential is measured on both others.

An asynchronous motor has its own. It is necessary to determine the minimum at which it will start rotating. After this, the value is gradually increased until all windings are aligned.

But when the engine spins up, it may turn out that equality is violated. This occurs due to a decrease in resistance. Therefore, before connecting an electric motor from 380 to 220 Volts and fixing this, you need to equalize the values ​​when the unit is running.

The voltage can be higher than 220 V. Make sure that stable connection of contacts is ensured and there is no loss of power or overheating. Switching is best done on special terminals with fixed bolts. After connecting the electric motor from 380 to 220 Volts with the necessary parameters, the casing is put on the unit again, and the wires are passed along the sides through a rubber seal.

What else can happen and how to solve problems

Often after assembly it is discovered that the shaft rotates in the wrong direction. The direction needs to be changed.

To do this, the third winding is connected through a capacitor to the threaded terminal of the second stator winding.

It happens that due to prolonged operation, engine noise appears over time. However, this sound is of a completely different type compared to the hum from an incorrect connection. Engine vibration also happens over time. Sometimes you even have to forcefully rotate the rotor. This is usually caused by worn bearings, causing excessive clearances and noise. Over time, this can lead to jamming, and later to damage to engine parts.

It is better not to allow this, otherwise the mechanism will become unusable. It's easier to replace the bearings with new ones. Then the electric motor will last for many years.

Home-grown “kulibins” use whatever they can get their hands on for electromechanical crafts. When choosing an electric motor, you usually come across three-phase asynchronous ones. This type has become widespread due to its successful design, good balancing and efficiency.

This is especially true in powerful industrial units. Outside a private house or apartment, there are no problems with three-phase power. How to organize the connection of a three-phase motor to a single-phase network if your meter has two wires?

Let's consider the standard connection option

Three-phase motor, has three windings at an angle of 120°. Three pairs of contacts are output to the terminal block. The connection can be organized in two ways:

Star and delta connection

Each winding is connected at one end to two other windings, forming the so-called neutral. The remaining ends are connected to the three phases. Thus, 380 volts are supplied to each pair of windings:

In the distribution block, the jumpers are connected accordingly, it is impossible to mix up the contacts. There is no concept of polarity in alternating current, so it does not matter which phase or wire is applied to.

With this method, the end of each winding is connected to the next, resulting in a closed circle, or rather a triangle. Each winding has a voltage of 380 volts.

Connection diagram:

Accordingly, the jumpers on the terminal block are installed differently. Similar to the first option, there is no polarity as a class.

Each group of contacts receives current at different times, following the concept of “phase shift”. Therefore, the magnetic field consistently pulls the rotor along with it, creating a continuous torque. This is how the engine works with its “native” three-phase power supply.

What if you received an engine in excellent condition, but you need to connect it to a single-phase network? Don’t be upset; the connection diagram for a three-phase motor has been worked out by engineers a long time ago. We will share with you the secrets of several popular options.

Connecting a three-phase motor to a 220 volt network (single phase)

At first glance, the operation of a three-phase motor when connected to one phase is no different from being turned on correctly. The rotor rotates, practically without losing speed, no jerks or slowdowns are observed.

However, it is impossible to achieve standard power with such a power supply. This is a forced loss, there is no way to fix it, you have to reckon with it. Depending on the control circuit, the power reduction ranges from 20% to 50%.

At the same time, electricity is consumed in the same way as if you were using all the power. To choose the most profitable option, we suggest that you familiarize yourself with the various methods.

It happens that a three-phase electric motor falls into your hands. It is from such engines that homemade circular saws, emery machines and various types of shredders are made. In general, a good owner knows what can be done with it. But the trouble is, a three-phase network in private homes is very rare, and it is not always possible to install it. But there are several ways to connect such a motor to a 220V network.

It should be understood that the engine power with such a connection, no matter how hard you try, will drop noticeably. Thus, a delta connection uses only 70% of the engine power, and a star connection uses even less - only 50%.

In this regard, it is desirable to have a more powerful engine.

Important! When connecting the motor, be extremely careful. Take your time. When changing the circuit, turn off the power supply and discharge the capacitor with an electric lamp. Work with at least two people.

So, in any connection scheme, capacitors are used. In essence, they act as the third phase. Thanks to it, the phase to which one terminal of the capacitor is connected shifts exactly as much as necessary to simulate the third phase. Moreover, to operate the engine, one capacity is used (working), and for starting, another (starting) is used in parallel with the working one. Although this is not always necessary.

For example, for a lawn mower with a blade in the form of a sharpened blade, a 1 kW unit and only working capacitors will be sufficient, without the need for containers for starting. This is due to the fact that the engine is idling when starting and it has enough energy to spin the shaft.

If you take a circular saw, a hood or another device that puts an initial load on the shaft, then you cannot do without additional banks of capacitors for starting. Someone may say: “why not connect the maximum capacity so that there is not enough?” But it's not that simple. With such a connection, the motor will overheat and may fail. Don't risk your equipment.

Important! Whatever the capacitance of the capacitors, their operating voltage must be at least 400V, otherwise they will not work for a long time and may explode.

Let's first consider how a three-phase motor is connected to a 380V network.

Three-phase motors come with either three terminals - for connection to a star only - or with six connections, with the ability to select a circuit - star or delta. The classic scheme can be seen in the figure. Here in the picture on the left there is a star connection. The photo on the right shows how it looks on a real engine frame.

It can be seen that for this it is necessary to install special jumpers on the required pins. These jumpers come with the motor. In the case where there are only 3 terminals, the star connection is already made inside the motor housing. In this case, it is simply impossible to change the winding connection diagram.

Some say that they did this to prevent workers from stealing units from home for their own needs. Be that as it may, such engine options can be successfully used for garage purposes, but their power will be noticeably lower than those connected by a triangle.

Connection diagram for a 3-phase motor in a 220V network connected by a star.

As you can see, the 220V voltage is distributed over two series-connected windings, where each is designed for such a 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 380V motor in a 220V network can only 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. The connection diagram for such an electric motor is shown in Figure 1.

Fig. 2 shows a terminal with a 6-pin terminal for delta connection. The three resulting outputs are supplied with: phase, zero and one terminal of the capacitor. The direction of rotation of the electric motor depends on where the second terminal of the capacitor is connected - phase or zero.

In the photo: an electric motor with only working capacitors and no capacitors for starting.

If there is an initial load on the shaft, it is necessary to use capacitors for starting. They are connected in parallel with the workers using a button or switch at the time of switching on. As soon as the engine reaches maximum speed, the starting tanks should be disconnected from the workers. If it is a button, we simply release it, and if it is a switch, then we turn it off. Then the engine uses only working capacitors. Such a connection is shown in the photo.

How to select capacitors for a three-phase motor using it in a 220V network.

The first thing you need to know is that the capacitors must be non-polar, that is, not electrolytic. It is best to use containers of the brand ― MBGO. They were successfully used in the USSR and in our time. They perfectly withstand voltage, current surges and the damaging effects of the environment.

They also have mounting eyes that help you easily place them at any point on the device’s body. Unfortunately, getting them now is problematic, but there are many other modern capacitors that are no worse than the first ones. The main thing is that, as mentioned above, their operating voltage is not less than 400V.

Calculation of capacitors. Working capacitor capacity.

In order not to resort to long formulas and torture your brain, there is a simple way to calculate a capacitor for a 380V motor. For every 100 W (0.1 kW) 7 µF is taken. For example, if the motor is 1 kW, then we calculate it like this: 7 * 10 = 70 µF. It is extremely difficult to find such a capacity in one jar, and it is also expensive. Therefore, most often the containers are connected in parallel, gaining the required capacity.

Starting capacitor capacity.

This value is taken at the rate of 2-3 times greater than the capacity of the working capacitor. It should be taken into account that this capacity is taken in total with the working capacity, that is, for a 1 kW motor, the working capacity is equal to 70 μF, multiply it by 2 or 3, and get the required value. This is 70-140 µF of additional capacitance - starting. At the moment of switching on, it is connected to the working one and the total is 140-210 µF.

Features of the selection of capacitors.

Capacitors, both working and starting, 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.

Many zealous owners who are accustomed to doing everything as much as possible with their own hands have to face this problem. Including collecting various equipment for household needs; for example, a circular saw on the site, an electric sander, a small lift in the garage, and the like.

Considering how much an electric motor costs, it is better to adapt the 3-phase sample at hand to work from 1ph, thereby adapting it to the home electrical network, than to purchase a new one. You just need to understand how and which electric motor is better to convert from 380 volts to 220, so as not to spend additional money, and understand the existing circuits for connecting them.

1. Converting from 380 to 220 makes sense if we are talking about an electric motor of relatively low power - up to 2.5, but not more (this is a maximum) 3 kW. In principle, there are no restrictions on this characteristic. But at the same time, most likely, you will need to carry out a number of activities and spend a certain amount of money and time.

• Relocate the power supply cable, and you will also have to negotiate with the electricity supplier in terms of increasing the limit. We should not forget that for private households there is a limit on en/consumption; usually 15 kW. Will a new load in the form of a powerful electric motor “fit” into it? Will the originally installed cable withstand it?
• For such a device, you need to lay a separate line from the power panel and install an individual machine, at a minimum. It’s unlikely that you’ll be able to simply connect it through an outlet; It's better not to experiment.

• The practice of rework shows that even if everything is done correctly, another problem will arise with the launch. The “start” of a powerful electric motor will be difficult, with prolonged build-up and voltage surges. Few people will be happy with this prospect, especially if something is being assembled not on a suburban site, but on the territory adjacent to a residential building. While the homemade installation based on this engine is functioning, malfunctions in the operation of household appliances will begin. Tested more than once.

1. The procedure for reworking depends on the internal circuit of the electric motor. In some models, only 3 wires are output to the terminal box, in others - 6.

What is the difference? In the first case, the windings are already connected according to one of the traditional circuits - “star” or “delta”, so there are somewhat less possibilities for maneuver (in terms of modification).

There are few options - leave the original connection or disassemble the engine and reconnect the other ends. If all six are output, then you can connect them according to any of the schemes, without restrictions. The main thing is to wisely choose the one that will be optimal for a specific situation (electric motor power, the specifics of its application). .

How to convert an electric motor

Scheme

Considering that the power of the electric motor is small (which means you won’t have to “rip it off” during startup), and it is planned to be powered from a 220 network, the optimal circuit is a “triangle”. That is, there is no need to focus on high starting currents (there won’t be any), and the power loss is practically reduced to zero (you can ignore it). All of the above is clearly demonstrated by the drawing.

If the circuit in the electric motor is initially assembled in a “triangle”, then nothing needs to be altered in it at all.

Calculation of working tanks

Since instead of 3 phases there will now be only one, it is supplied to each of the windings, but with a slight shift of the sinusoid. In fact, turning on the capacitors simulates the power supply to the electric motor from a 380/3 ph source. Formulas for calculating working capacitors are shown in the figures below.

You shouldn’t install them according to the “bigger is better” principle, which is what home craftsmen who are not particularly versed in electrical engineering often do. Only based on calculations of the required denomination. Otherwise, the electric motor may overheat. If it is installed on factory equipment (for example, a lawn mower is being rebuilt), then you will either have to take constant breaks in work, or prepare for unplanned repairs and unjustified financial expenses on a new “engine”.

Note:

• Capacitances for the electric motor windings are selected not only by nominal value, but also by operating voltage. Since we are talking about converting from 380 to 220, then U p should be at least 400 V.
• Another important factor is the type of capacitors. Firstly, they must be of the same type. Secondly, just not electrolytic ones. Optimally, paper; for example, the outdated KGB, MBG series (and their modifications) or its modern analogues. They are easy to mount (they have eyes) and can easily withstand fluctuations in temperature, current, and voltage.

For the star circuit

For the triangle pattern

You can clearly see the whole process in action in the video:

In practice, few knowledgeable people are involved in engineering calculations. There are certain proportions that allow you to quite accurately select a working capacitor for a specific electric motor.

The ratio is easy to remember: for every 100 W of engine power - 7 microfarads of working capacity. That is, for a 2 kW product you will need to include capacitors of 7 x 20 = 140 uF in the windings.

What's the difficulty? It is unlikely that you will be able to find a container with such a rating. There is a simple solution - take several capacitors and connect them in parallel. As a result of small calculations, it is easy to select the required number of them with the total capacity of the required value. For those who have forgotten school, I can give you a hint: with this method of connecting capacitors, their capacitances are added together.

Launcher

This capacity is not always needed. It is placed in the circuit only if, when starting, a significant load is created on the motor shaft. Examples - a powerful exhaust device, a circular saw. But for the same lawn mower, working capacitors are quite enough.

The calculation is simple - the nominal value of Cn must exceed Cr by 2.5 (plus/minus). Here extreme precision is not required; The value of the starting capacitance is determined approximately. Further analysis of the operation of the electric motor in different modes will tell you whether to increase or decrease it.

By the way, this also applies to working capacitors. The fact is that all calculations a priori assume that the electric motor is new and has never been in operation. And since mostly used products are remade, during the process it will become clear what the user is not happy with. There are many options - poor startup, rapid heating of the case, and so on.

Conclusion - selecting containers for converting an electric engine from 380 to 220, that's not all. At first, you need to carefully monitor its operation in various modes. Only in this way, experimentally, by replacing capacitors according to their ratings, can you select the ideal capacitance value for a particular product.

How to organize reverse

Sometimes it is necessary to change the direction of rotation of the shaft without additional modifications. This is quite possible for a 380 electric motor switched to 220 power. As can be seen from the figure, there is nothing complicated about this; you only need a 2-position switch.

On a note

There are three-phase electric motors that can operate from 220 V. Their inclusion in the home network has its own specifics - only as a “star”. The fact is that each of the windings is designed for 127, and when connected with a “triangle” they will simply burn out.

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 the 380 V network.

Online calculation of motor capacitor capacity

There is a special formula that can be used to calculate the required capacity accurately, but you can easily get by with an online calculator or recommendations that are derived from many experiments:

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.

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”.