Is it possible to use a starting capacitor working. How to connect a single-phase electric motor through a capacitor: starting, working and mixed switching options. Wiring diagrams of a three-phase motor to a single-phase network

An asynchronous three-phase motor can be connected without much damage to a conventional single-phase electrical network through capacitors. With their help, the launch and achievement of the desired operating modes with such a power system is ensured. Distinguish between worker and starting capacitors.

Differences between them

They consist in their purpose, capacity, method of connection, as well as in working conditions. The first difference is that the worker (first) the capacitor serves to shift the phases... As a result, a rotating magnetic field appears between the windings, which is necessary to drive the motor without mechanical load. Such an electric motor is installed, for example, in a grinding machine.

Starting (second) provides an increase in the starting torque of the motorunder mechanical stress, making it easier to reach desired mode... The resources of one worker may not be enough, which is why the rotor of the engine simply will not start rotating. The use is justified in conjunction with machine tools, lifting mechanisms, pumps and similar heavy devices. It can also be used with a more powerful three-phase motor if there is not enough worker to start it reliably.

The capacitance of both capacitors will also differ. It is directly proportional to the power of the electric motor and inversely to the mains voltage. A correction factor is introduced depending on the connection diagram of the windings. The capacity of the launcher can be twice that of the worker.

Connection methods

The first capacitor in the most common case is connected to the rupture of one of the windings of an induction motor, which is also often called "auxiliary". The other is connected directly to the electrical network, and the third remains unused. The type of this scheme is called "star". There is also a delta connection. It differs in both the connection method and the complexity.

The second capacitive element, in contrast to the working one, is connected in parallel with the last one through a button or a centrifugal switch. In the first case, the control is carried out by a person, and in the second - by the drive itself. Both of these switches briefly close this circuit at the time the electric motor is started, and after it enters the operating mode, they open it.

Working conditions

They are different for each of the capacitors. Since the first of them is permanently connected to the motor winding, this circuit forms an elementary oscillatory circuit. Because of this, at certain moments, a voltage is generated at its terminals that exceeds the input by two and a half to three times. This circumstance should be taken into account when selecting, it is necessary to focus on parts designed for 500-600 volts.

Starting capacitors for electric motors - 220 V work in other, less harsh conditions, in contrast to the working ones. The voltage applied to this capacitive element exceeds the main voltage by about 1.15 times. It joins the circuits from time to time, which also has a positive effect on its working conditions, and significantly extends its service life.

The most commonly used domestic paper or oil-filled capacitors brands MBGO or MBGCH. Their advantage is their resistance to high AC voltages. But there is also a drawback - the large size. Oxide capacitors can be used as an alternative solution. They are not connected directly, but through diodes, according to certain schemes.

Conventional electrolytic capacitors used in various devices, and designed for considerable operating voltages, are suitable for asynchronous motors only as starting motors. This is due to the fact that a large reactive power passes through them due to the low resistance of the windings. Connecting capacitive elements with violations or deviations from the circuit will lead to damage or boiling of the electrolyte, which can harm the motor and personnel.

So, you can deduce from this a few tips, how to distinguish a starting capacitor from a working one:

• The first of these plays a supporting role. It is connected in parallel with the working one during the start of the motor - for a few seconds to facilitate the start.
• The second of them is connected permanently, providing the necessary phase shift, as a result of which a three-phase motor can operate from a single-phase network.

If you mix up the capacitors, then serious problems arise. The capacity of the worker should also not be too large, otherwise the motor will heat up, and the increase in power and torque from this will increase slightly.

In one of the previous articles, we talked about the selection of working capacitors for the operation of a 3 ph. (380 Volt) asynchronous electric motor from 1 ph. network (220 volts). Namely about. Thank you, my readers for the many reviews and thanks, because if it were not for you, you would have abandoned this business long ago. In one of the letters sent to me by mail, there were questions: "Why didn't I tell you about the starting capacitors?", "Why doesn't the engine start, because I did everything as it was written." But the truth is that there are not always enough "working" capacitors to start an electric motor under load, and the question arises: "What to do?" And here's what: "We need starting capacitors." But now we will talk about how to choose them correctly.

And so we have: a 3-phase electric motor, to which, on the basis, we selected the capacity of the working capacitor 60 μF. For the starting capacitor, we take the capacity 2 - 2.5 times more than the capacity of the working capacitor. Thus, we need a capacitor with a capacity of 120 - 150 μF. In this case, the operating voltage of these capacitors must be 1.5 times the mains voltage. Now many people have a question: "Why not 300 uF or even 1000 uF, because you can't spoil porridge with butter?" But in not this case, everything should be in moderation, with too much capacity of the starting capacitors, there is nothing very terrible not to happen, but the efficiency of starting the electric motor will be worse. Thus, you should not spend extra money on buying too much capacity.

But what kind of capacitors are needed to start an electric motor?

If we need a small starting capacitor, then capacitors of the same type that we used for working capacitors are quite suitable. But if we need a fairly large capacity? For this purpose, it is not advisable to use this type of capacitors due to their high cost and size (when assembling a large capacitor bank, its dimensions will be large). For such purposes, we use special starting (starting) capacitors, which are now on sale in a large assortment. Such capacitors are found in different shapes and types, but their names contain markings (inscriptions): "Start", "Starting", "Motor Start" or something like that, they all serve to start the electric motor. But for better persuasiveness, it is better to ask the seller when buying, he will always prompt.

But now you will say: "But what about the capacitors from old Soviet b / w TVs, the so-called" electrolytes "?

What can I tell you about this. I myself do not use them, and I do not recommend them and even discourage them. This is because their use as starting capacitors is not entirely safe. Because they can swell or, even worse, explode. In addition, this type of capacitor dries out over time and loses its nominal capacity, and we cannot know exactly which one we are using at the moment.

And so we have an electric motor, a working and starting capacitor. How do we connect all this?

For this we need the PNVS button.

The PNVS button (push-button starter with a starting contact) has three contacts: two extreme contacts with latching and one in the middle without latching. It serves to turn on the starting capacitor, and when you stop pressing the button, it returns to its original position (the starting capacitor "Cn" turns on only when the engine is started, and the working capacitor "Cp" is constantly in operation), the other two extreme contacts remain on and are disabled when the Stop button is pressed. The "Start" button must be held until the shaft speed reaches the maximum speed, and only then release it. Also, do not forget that a capacitor has the property of having an electric charge, and you can get electrocuted. Whatever happens, at the end of the work, disconnect the electric motor from the network, and turn on the "Start" button for one or two seconds so that the capacitors can be discharged. Or, in parallel with the starting capacitor, put a resistor of about 100 kilohms so that the capacitor is discharged to it.

It is good if you can connect the motor to the required type of voltage. And if there is no such possibility? This becomes a headache since not everyone knows how to use the three-phase version of the motor based on single-phase networks. This problem appears in various cases, it may be necessary to use a motor for an emery or drilling machine - capacitors will help. But they are of many types, and not everyone will be able to understand them.

So that you get an idea of \u200b\u200btheir functionality, we will further figure out how to choose a capacitor for an electric motor. First of all, we recommend that you determine the correct capacity of this auxiliary device, and how to accurately calculate it.

What is a capacitor?

Its device is simple and reliable - inside two parallel plates in the space between them, a dielectric is installed, which is necessary for protection against polarization in the form of a charge created by conductors. But different types of capacitors for electric motors are different, so it is easy to make a mistake at the time of purchase.

Let's consider them separately:

Polar versions are not suitable for connection based on AC voltage, since the risk of dielectric disappearance increases, which will inevitably lead to overheating and an emergency situation - fire or a short circuit.

Versions of the non-polar type are distinguished by high-quality interaction with any voltage, which is due to the universal version of the plate - it is successfully combined with increased current power and various types of dielectrics.

Electrolytic, often referred to as oxide, are considered the best for low frequency motors as their maximum capacitance can be as high as 100,000 μF. This is possible due to the thin type of oxide film included in the structure as an electrode.

Now check out the photo of capacitors for an electric motor - this will help distinguish them in appearance. This information will come in handy at the time of purchase, and will help you purchase the necessary device, since they are all similar. But the help of the seller may also be useful - it is worth using his knowledge if you do not have enough of your own.

If you need a capacitor to work with a three-phase electric motor

It is necessary to correctly calculate the capacitance of the capacitor of the electric motor, which can be done using a complex formula or using a simplified method. To do this, the power of the electric motor is specified for every 100 watts, it will take about 7-8 μF from the capacitor capacity.

But during the calculations, it is necessary to take into account the level of voltage impact on the stator winding part. It cannot exceed the nominal level.

If starting the engine can only occur based on the maximum load, you will have to add a starting capacitor. It is distinguished by its short duration of operation, since it is used about 3 seconds before reaching the peak of the rotor speed.

It must be borne in mind that it will require a power increased by 1.5, and the capacity is approximately 2.5 - 3 times than that of the network version of the capacitor.

If you need a capacitor to work with a single-phase electric motor

Typically, various capacitors for asynchronous motors are used to operate with a voltage of 220 V, taking into account the installation in a single-phase network.

But the process of using them is a little more complicated, since three-phase electric motors operate using a constructive connection, and for single-phase versions, it will be necessary to provide an offset torque at the rotor. This is achieved by using an increased amount of winding to start, and the phase is shifted by the forces of the capacitor.

What is the difficulty in choosing such a capacitor?

In principle, there is no greater difference, but different capacitors for asynchronous motors will require a different calculation of the permissible voltage. It will take about 100 watts for each μF of device capacitance. And they differ in the available modes of operation of electric motors:

• A starting capacitor and a layer of additional winding are used (only for the starting process), then the calculation of the capacitance of the capacitor is 70 μF for 1 kW of the power of the electric motor;
• A working version of a capacitor with a capacity of 25 - 35 μF is used based on an additional winding with a permanent connection during the entire duration of the device's operation;
• A working version of the capacitor is used based on the parallel connection of the starting version.

But in any case, it is necessary to monitor the level of heating of the engine elements during its operation. If overheating is noticed then action must be taken.

In the case of a working version of the capacitor, we recommend reducing its capacity. We recommend using capacitors based on 450 volts or more as they are considered the best option.

To avoid unpleasant moments before connecting to the electric motor, we recommend that you make sure that the capacitor is working with a multimeter. In the process of creating the necessary connection with the electric motor, the user can create a fully functional circuit.

Almost always, the leads of the windings and capacitors are located in the terminal part of the motor housing. Due to this, you can create virtually any modernization.

Important: The starting version of the capacitor must have an operating voltage of at least 400 V, which is associated with the appearance of a surge of increased power up to 300 - 600 V that occurs during the start or shutdown of the engine.

So, what is the difference between a single-phase asynchronous version of an electric motor? Let's look at this in detail:

• It is often used for household appliances;
• To start it, an additional winding is used and an element for phase shifting is required - a capacitor;
• Connects on the basis of many circuits using a capacitor;
• The starting version of the capacitor is used to improve the starting torque, and the performance is increased with the working version of the capacitor.

Now you have the information you need and know how to connect a capacitor to an induction motor for maximum efficiency. And you also have knowledge about capacitors and how to use them.

Photo of capacitors for an electric motor

Many owners quite often find themselves in a situation where they need to connect in the garage or in the country a device such as a three-phase asynchronous motor to various equipment, which can be an emery or drilling machine. This raises a problem, since the source is designed for single phase voltage. What to do here? In fact, this problem can be solved quite easily by connecting the unit according to the circuits used for condensing units. To realize this idea, a working and starting device will be required, often referred to as phase shifters.

Capacity selection

To ensure the correct operation of the electric motor, certain parameters must be calculated.

For working capacitor

To select the effective capacity of the device, it is necessary to perform calculations using the formula:

• I1 is the nominal value of the stator current, for the measurement of which special clamps are used;
• Umains - network voltage with one phase, (V).

After performing the calculations, the capacity of the working capacitor in μF will be obtained.

It may be difficult for someone to calculate this parameter using the above formula. However, in this case, you can use another scheme for calculating the capacity, where it is not necessary to carry out such complex operations. This method makes it quite easy to determine the required parameter based only on the power of the induction motor.

It is enough to remember here that 100 watts of power of a three-phase unit should correspond to about 7 μF of the capacity of the working capacitor.

When calculating, you need to monitor the current that flows to the phase stator winding in the selected mode. It is considered unacceptable if the current is greater than the nominal value.

For starting capacitor

There are situations when the electric motor has to be turned on under conditions of heavy load on the shaft. Then one working capacitor will not be enough, so a starting capacitor will have to be added to it. A feature of its work is that it will work only during the launch of the device no more than 3 seconds, which is used by the SA key. When the rotor reaches the level of the rated speed, the device turns off.

If, through an oversight, the owner left the starting devices turned on, this will lead to the formation of a significant imbalance in the currents in the phases. In such situations, the possibility of engine overheating is high. When determining the capacitance, one should proceed from the fact that the value of this parameter should be 2.5-3 times higher than the capacity of the working capacitor. By doing so, it is possible to ensure that the starting torque of the engine reaches the rated value, so that no complications arise during starting.

To create the required capacitance, capacitors can be connected in parallel and in series. It should be borne in mind that the operation of three-phase units with a capacity of not more than 1 kW is allowed if they are connected to a single-phase network in the presence of a working device. And here you can do without a starting capacitor.

A type

After calculations, you need to determine what type of capacitor can be used for the selected circuit

The best option is when the same type is used for both capacitors. Usually, the operation of a three-phase motor is provided by paper starting capacitors, clothed in a steel sealed case such as MPGO, MBGP, KBP or MBGO.

Most of these devices are rectangular in shape. If you look at the case, then there are their characteristics:

• Capacitance (μF);
• Working voltage (V).

Application of electrolytic devices

When using paper starting capacitors, you need to remember the following negative point: they have quite big sizeswhile providing a small capacity. For this reason, for the efficient operation of a three-phase motor of low power, it is necessary to use enough a large number of capacitors. If desired, paper can be replaced with electrolytic ones. In this case, they must be connected in a slightly different way, where additional elements, represented by diodes and resistors, must be present.

However, experts advise against using electrolytic starting capacitors. This is due to the fact that they have a serious drawback, which manifests itself in the following: if the diode does not cope with its task, alternating current will be sold to the device, and this is already fraught with its heating and subsequent explosion.

Another reason is that today on the market you can find improved with a metallized coating polypropylene AC starting models of the SVV type.

Most often, they are designed to work with a voltage of 400-450 V. They should be given preference, given that they have repeatedly shown themselves to be on the good side.

Voltage

Considering the various types of starting rectifiers for a three-phase motor connected to a single-phase network, one should take into account such a parameter as the operating voltage.

A mistake will be the use of a rectifier whose voltage indicator exceeds the required one by an order of magnitude. In addition to the high costs of purchasing it, you will have to allocate more space for it due to its large dimensions.

At the same time, you should not consider models in which the voltage has a lower indicator than the mains voltage. Devices with such characteristics will not be able to effectively perform their functions and will fail pretty soon.

To reduce to not making a mistake when choosing the operating voltage, you should adhere to the following calculation scheme: the final parameter must correspond to the product of the actual mains voltage and the coefficient 1.15, while the calculated value must be at least 300 V.

In the event that paper rectifiers are selected for operation in an alternating voltage network, then their operating voltage must be divided by 1.5-2. Therefore, the operating voltage for a paper capacitor, for which the manufacturer indicated a voltage of 180 V, will be 90-120 V.

In order to understand how the idea of \u200b\u200bconnecting a three-phase electric motor to a single-phase network is realized in practice, we will perform an experiment using an AOL 22-4 unit with a power of 400 (W). The main task that must be solved is starting the engine from a single-phase network with a voltage of 220 V.

The used electric motor has the following characteristics:

Keeping in mind that the electric motor used has a low power, when connecting it to a single-phase network, you can buy only a working capacitor.

Calculation of the capacity of the working rectifier:

Using the above formulas, we take the average value of the capacitance of the working rectifier to be 25 μF. Here, a slightly larger capacitance of 10 μF was chosen. So we will try to find out how such a change affects the launch of the apparatus.

Now we need to buy rectifiers, capacitors of the MBGO type will be used as the latter. Further, on the basis of the prepared rectifiers, the required capacity is assembled.

In the process, it should be remembered that each such rectifier has a capacity of 10 μF.

If you take two capacitors and connect them to each other in parallel, the total capacitance will be 20 μF. In this case, the indicator of the operating voltage will be 160V. To achieve the required level of 320 V, it is necessary to take these two rectifiers and connect them to the same pair of capacitors connected in parallel, but using a series circuit. As a result, the total capacity will be 10 μF. When the battery of working capacitors is ready, we connect it to the engine. Then it remains only to run it in a single-phase network.

In the course of the experiment with connecting the motor to a single-phase network, the work required less time and effort. Using a similar unit with a selected battery of rectifiers, it should be noted that its useful power will be at the level of up to 70-80% of the rated power, while the rotor speed will correspond to the rated indicator.

Important: if the motor used is designed for a 380/220 V network, then when connecting to the network, use the "delta" scheme.

Pay attention to the content of the tag: it so happens that there is an image of a star with a voltage of 380 V. In this case correct work the motor in the network can be provided by fulfilling the following conditions. First, you have to "gut" the common star, and then connect 6 ends to the terminal block. Search for a common point should be in the front of the engine.

Video: connecting a single-phase motor to a single-phase network

The decision to use a starting capacitor should be made based on specific conditions, most often a working one is sufficient. However, if the motor used is subject to increased load, it is recommended to stop operation. In this case, it is necessary to correctly determine the required capacity of the device in order to ensure the efficient operation of the unit.