Connecting a capacitor motor. Correct connection of a single-phase motor

Sometimes the question arises of how the connection is made single phase motor to power supplies and networks. single phase asynchronous electric motors are the most common, since they are installed on the vast majority of various household appliances and equipment (computer, etc.). Sometimes such engines are purchased and installed in workshops, garages, etc. to ensure that any work is carried out (for example, lifting a load).

Single-phase asynchronous electric motors are installed on the vast majority of various household appliances and appliances.

The work requires connecting a single-phase electric motor, and this is quite difficult for a person who does not understand electrical engineering and electric drives. The difficulty comes from the fact that the motor has many leads, and the amateur has difficulty because he does not know which lead to connect to the power supply. Therefore, this material considers connection issues specifically for the average citizen who has no idea about the electric drive and does not understand electrical engineering.

Machine Description

Single-phase electric motors are usually called asynchronous single-phase electric machines with low power. The magnetic circuit of such machines has a two-phase winding, which is divided into starting (starting) and main. The need for 2 windings is as follows: they must cause the rotor to rotate in an electric propulsor (single-phase). At the moment, such devices are conventionally divided into 2 categories:

1. The presence of starting windings. In this embodiment, the starting winding is connected through a starting capacitor. When the start is completed and the machine has reached its rated speed, starting winding turns off the power. After that, the engine continues to rotate on the working winding connected to the network (the capacitor is charged at start-up and turns off the start winding). The required volume of the condenser is standardly indicated by the manufacturer of the machine on a plate with all the parameters (it should be standard on all engines).
2. Machines with running capacitors. In such electrical machines, the auxiliary windings are always connected through capacitors. In this case, the volume of capacitors is determined by the design of the motor. In this case, the capacitor remains on even when the machine reaches the nominal operating mode.

To properly connect electrical machine, you must be able to determine (or know) how the starting and working windings are derived, as well as their characteristics.

It is worth noting: these windings are different in the conductors used (their cross section), as well as in turns. So for working windings, conductors of a larger cross section are used, and they have a greater number of turns. It is important to know that the resistance of the working windings for different machines is always less than the resistance of the starting / auxiliary ones. At the same time, it is not difficult to measure the resistance of the motor winding, especially if special multimeters are used.

Based on the above, it is worth giving some examples.

Connection examples

Here we consider 3 options for propulsion, which differ from each other.

Option number 1. The mover has 4 outputs. First, the ends of the windings are found (usually they are arranged in pairs, so it is not difficult to see them).

There can be 2 options for the location of the conclusions: either all 4 in one row, or 2 in one row and 2 in the second. In the first case, it is easier to determine the windings: the first pair is one winding, the second is the other.

In the second case, you can get confused between the windings. The most common option is when one vertical row is one winding, the other is the second. But it is worth knowing that the multimeter will give an infinite resistance value if the conclusions of different windings are selected. And then everything is simple.

The resistance of the windings is determined: where there is less resistance, it is the working one, and the larger one is the starting one.

The connection is carried out as follows: 220 V is supplied to the thick wires, and one starting terminal is connected to the working terminal. At the same time, you should not worry about the correct connection of the conclusions - the operation of the machine and the direction in which the rotation is carried out will not change depending on which end was connected to which. The direction of rotation changes due to the change in the ends of the connection of the starting winding.

The second option is when the machine has 3 outputs. In this case, when measuring the resistance between the windings, the multimeter will show various meanings- minimum, maximum, average (if they are measured in pairs). Here, the common end, which will have the minimum and average value, is one of the connection ends, the other output for connecting the network is the one that has the minimum value. The output that remains - the output of the starting winding - must be connected with a capacitor and with one of the ends of the mains supply. In this case, it is not possible to independently change the direction of rotation.

Last example. There are 3 outputs, and measurements of the resistance between the outputs in pairs showed that there are 2 absolutely identical values ​​​​and one more (about 2 times). Such movers were often installed on old ones and are installed on modern washing machines. This is exactly the case when the windings of the machine are identical, so it makes absolutely no difference how to connect the windings.

How to put it into practice? This is the most frequently asked question, because connecting tools (grinders, punchers, screwdrivers, etc.) can be difficult. This is sometimes due to the fact that the tool uses a collector mover, which often works without starting devices. Let's consider this option in more detail.

Starting a motor with a collector

This case is the most common. In the chapter above, it is indicated under example No. 3. These engines are often used for home appliances because they are simple and cheap.

Usually the ends of such engines are numbered. Therefore, to connect, connect pins 2 and 3 to each other (one comes from the armature and the other from the stator), and connect numbers 1 and 2 to the power source.

You should be aware that if you connect such a machine without special electronic devices, then it will only give the maximum number of revolutions and speed control will not be possible. In this case, there will be a large starting current and jerking force at start-up.

If a change in the direction of rotation of the propulsor is required, then the connection of the stator or armature leads should be reversed.

Practical connection

If there is a motor that should be connected to the network, then you need to carefully study its plate, which shows the nominal values ​​\u200b\u200bof the machine and the capacitor (or several capacitors). Further, by the name of the model of the electric machine, it is recommended to find a diagram.

The connection diagram of a single-phase electric motor for different devices may be different, so it is recommended to choose a diagram for a specific option. Otherwise, problems may arise, up to the complete failure of the mover (when it burns out). Next, you should pick up the capacitor (if it is out of order or not). The selection is carried out according to special tables that are in the reference literature.

Let's take a washing machine as an example. recent years release. There, a collector or three-phase mover is usually used. If there is a three-phase mover, it can only be started by connecting a special starting block, which must be selected for a specific model of the washing machine.

In the case of a collector machine, about 7 wires (± 1) will be output to the terminal block, excluding the ground terminal (it is marked with the appropriate sign, and a yellow-green wire goes to it). A pair of pins usually has a tachometer, they are not connected to the network. And 2 outputs each have a stator and a rotor of an electric machine and an alphanumeric marking (for example, A1-a1, or A-a). The first letter (capital) indicates the beginning of the winding, the second - the end. The other winding is indicated by the next letter of the Latin alphabet. Power is supplied to the beginning of the rotor and the end of the stator winding. To do this, you must first decide on the winding (which one from where). After that, the free conclusions of the windings are connected using a jumper.

After that, a test run of the device should be carried out, moreover, observing the safety regulations.

Single-phase asynchronous electric motors up to 1 kW, rarely up to 2 kW, are widely used in conditions where there is only single-phase network, for example, to drive the mechanisms of various devices, electrified tools, in household mechanisms, etc. If the motor winding is powered single-phase current, then the electromagnetic field in it will not be rotating, as in three-phase machines, but pulsating, the energy indicators will become worse than that of three-phase ones, but. Starting torque will be equal to zero, i.e. the engine will not start without special devices. Therefore, in the stators of single-phase motors, two windings are installed, which are often also called winding phases. One of them is the main, or working, the other is auxiliary. The windings are located along the stator slots so that their axes are shifted relative to each other in space by an electrical angle of 90° (Fig. 1).

Fig.1. The axes of the windings of two- and single-phase motors: a - the location of the coils different phases in the stator slots; b - conditional image of the phases of the winding.

If the phases of the winding currents are not the same, i.e., shifted in time, then the electromagnetic field in the motor stator becomes rotating. The energy performance of the engine improves and the starting torque appears. With a phase shift of the currents by an electrical angle of 90 ° and the same MMF of the windings, the field becomes circular and the efficiency of a single-phase motor will be the highest. This can be achieved by making both motor windings the same and connecting a capacitor in series to one of them (Fig. 2.a). Such motors are called single-phase capacitor motors.

Rice. 2 .. Schemes for switching on single-phase motors: a - with a permanently connected capacitor (capacitor motors); b - with working and starting capacitors; in - with a starting element; Cp - working capacitor; Sp - starting capacitor; PE - starting element.

The capacitance of the capacitor required to obtain a circular field depends on the active and inductive resistances of the motor windings and on its load. For single-phase capacitor motors, the capacitor is designed so that the field is circular at rated load. It is switched on in series with one of the phases of the windings for the entire time of operation. This capacitor is called a working capacitor and is designated Cp. During the start of the engine, the capacity of the working capacitor is insufficient for the formation of a circular field and the starting torque of the engine is small. To increase the starting torque, a second one is switched on in parallel with the working capacitor - the starting capacitor (Cp). The total capacitance of the starting and running capacitors provides a circular rotating field during engine start-up and its starting torque increases. After the engine accelerates, the starting capacitor is turned off, and the worker remains on (Fig. 2.b). Thus, the motor starts and runs at rated load with a rotating circular field.

Rice. 3. Scheme of a single-layer concentric winding with m = 2, z = 16, 2p = 2,
carried out at random.

In most stators, one and two-phase motors apply bulk single-layer windings with concentric coils (Fig. 3). They have either four outputs - the beginnings and ends of the main and auxiliary phases, or only three. With three leads, the ends of the main and auxiliary phases are connected to each other inside the case and the wire is brought out from the place of their connection common point windings.

Rice. 4. Scheme of a single-layer concentric winding with m = 2, z = 24, 2p = 4, q = 3, made with "combed" coils.

To reduce the overhang of the frontal parts of the coils, single-layer windings are often rolled. If the number of slots per pole and phase is even, then the waddle windings are essentially the same as those of three-phase machines. If the number q is odd, then big coils in groups they make them “combed”, i.e., they bend the frontal parts of half of their turns in one direction, and the second half in the other direction (Fig. 4).
The need to install capacitors increases the cost of single-phase motors, increases their size and reduces reliability, since capacitors fail more often than motors. Therefore, most single-phase induction motors are designed to work with only one - the main winding. However, in order for them to be started up, a second one is also installed - an auxiliary winding, which is often called the starting one. It is intended only to create a rotating field when starting the engine. Such single-phase motors are called motors with a starting phase (or with a starting winding).
The phase shift of the currents of the main (working) and starting windings is achieved by changing the resistance of the starting winding by connecting in series with it the so-called starting element (Fig. 2.c) - a capacitor or resistor (most often a cheaper resistor is used).
Starting windings, as a rule, differ from workers both in the number of turns, and in the number of coils, and in the wire cross section. They usually occupy 1/3 of all stator slots. In the remaining 2/3 of the grooves is the working winding. The connection diagrams and the number of poles of the working and starting windings are the same (Fig. 5).

Rice. 5. Scheme of a single-layer concentric winding of a single-phase motor with a starting phase with z \u003d 24, 2p \u003d 4; C1-C2 - main phase, B1-B2 - starting phase.

To avoid installing resistors that must be sized for the full starting current, many single-phase motors have a start winding with increased starting phase resistance. For this purpose, the starting winding is wound from a wire of a smaller cross section than the working one, or it is performed with a partially bifilar winding.

Rice. 6. Formation of bifilar coils.

In this case, the length of the wire increases, its active resistance increases, and the inductive reactance and MMF remain the same as without bifilar turns. In order to form bifilar turns, the starting winding coil is made of two sections with the opposite winding direction (Fig. 6). One section, the direction of winding of which coincides with the polarity required to start the machine, is called the main section, and the section with counter winding is called bifilar. The latter always has fewer turns than the main one. In the winding diagrams, coils with a partially bifilar winding are indicated by a loop (Fig. 7a). On fig. 7b shows a winding circuit with a starting phase having a partially bifilar winding. The main winding is made with concentric rolled coils. Loops at the coils of the starting phase indicate that the coils are made with partially bifilar winding.

Rice. 7. Winding diagram with coils having bifilar turns: a - image of coils with bifilar turns on the winding diagram, b - winding diagram with z \u003d 24, 2p \u003d 4.

In a winding with bifilar coils it must be taken into account that in each coil of the auxiliary phase, part of the turns is wound in opposite directions. This reduces the number of effective conductors in the slot, canceling out the effect of the same number of turns wound in the main direction, so to find the number of effective turns in the coil (effective conductors in the slot), twice the number of counter-wound turns must be subtracted from the total number. If, for example, there is a coil in the groove, in which there are only 81 turns, of which 22 are counter-wound, then the number of effective conductors in the groove will be: 81-2-22 = 37.
To determine the number of counter-wound turns with the total number of conductors in the groove and the number of effective conductors in the groove known, the reverse action must be performed, i.e., subtract the number of effective conductors from the total number and divide the result by two. With a total number of conductors of 81 and an effective number of 37, the number of counter-wound turns should be: (81-37) / 2 = 22.
A bifilar coil can be obtained by placing two coil sections in the same grooves, one of which rotates 180° around an axis parallel to the grooves. The right and left sides of the rotated section are then reversed.
The starting winding of single-phase motors is designed only for short-term operation - for the duration of the motor start-up. It must be disconnected from the mains immediately, as soon as the engine accelerates, otherwise it will overheat and the engine will fail. Such motors are used, for example, to drive compressors in all household refrigerators, drive washing machines etc. Starter relay installed on refrigerators and washing machines, turns on both motor windings, and after its acceleration, turns off the starting winding. The motor operates with one working winding switched on.

Equipped with single-phase electric motors a large number of low-power refrigeration units used in everyday life (home refrigerators, freezers, domestic air conditioners, small heat pumps...).
Despite being very widespread, single-phase motors with auxiliary windings are often underestimated compared to three-phase motors.
The purpose of this section is to study the connection rules single-phase electric motors, their repair and maintenance, as well as consideration of the components and elements necessary for their operation (capacitors, starting relays). Of course, we will not study how and why such motors rotate, but all the features of their use as motors for compressors refrigeration equipment we will try to explain.
A) Single-phase motors with auxiliary winding
Such motors, found in most small compressors, are powered by 220 V. They consist of two windings (see Fig. 53.1).

The main winding P, called ________
often the working winding, or in English Run (R), has a thick wire, which remains energized during the entire period of engine operation and passes the rated current of the engine.
Auxiliary winding A, also called the starting winding, or in English S (Start), has a thinner wire, therefore, greater resistance, which makes it easy to distinguish it from the main winding.

Auxiliary or starting winding, as the name suggests, is used to start the engine.
Indeed, if you try to start the engine by applying voltage only to the main winding (and not powering the auxiliary one), the motor will hum, but will not start to rotate. If the shaft is turned by hand at this point, the motor will start and rotate in the direction in which it was turned by hand. Of course, this method of starting is not at all suitable for practice, especially if the motor is hidden in a sealed casing.
The starting winding just serves to start the engine and provide a starting torque higher than the moment of resistance on the motor shaft.
Further, we will see that, as a rule, a capacitor is introduced into the circuit in series with the starting winding, providing the necessary phase shift (about 90 °) between the current in the main and starting windings. This artificial skew just allows you to start the engine.

Attention! All measurements must be made with great care and precision, especially if the engine model is unfamiliar to you or there is no winding connection diagram.

Accidental mixing of the main and auxiliary windings, as a rule, ends with the fact that shortly after the voltage is applied, the motor burns out!
Feel free to repeat the measurements several times and sketch out the motor circuit with as many marks as possible, this will allow you to avoid many mistakes!
NOTE
If the motor is three-phase, the ohmmeter will show same values resistance between all three terminals. Thus, it seems that it is difficult to make a mistake when calling this type of engine (according to three-phase motors see section 62).
In any case, get in the habit of reading the reference data on the motor case, and also think about how to look inside the terminal box by removing its cover, since there is often a diagram of the connection of the motor windings.

Engine check. One of the most difficult questions for a novice repairman is to decide that, according to the results of the check, the engine should be considered burned out. Recall the main electrical defects that are most common in motors (whether single-phase or three-phase). Most of these defects are caused by severe motor overheating due to excessive current consumption. An increase in current may be due to electrical (continuous voltage drop, overvoltage, poor tuning safety devices, poor electrical contact, defective contactor) or mechanical (jamming due to lack of oil) malfunctions, as well as anomalies in refrigeration circuit(too high condensing pressure, presence of acids in the circuit...).

One of the windings may be broken. In this case, the ohmmeter, when measuring its resistance, will show a very large value instead of normal resistance. Make sure your ohmmeter is working properly and that its clamps are good contact with winding terminals. Feel free to test the ohmmeter with a good standard.
Recall that the winding of a conventional motor has a maximum resistance of several tens of ohms for small motors and several tenths of an ohm for huge motors. If the winding is broken, it will be necessary either to replace the motor (or the entire assembly) or rewind it (in the case where this is possible, rewinding is all the more beneficial, the greater the engine power).
Between two windings there can exist short circuit. To perform this test, the connecting wires (and connecting jumpers on a three-phase motor) must be removed.
When you disconnect, never hesitate to pre-develop a detailed measurement scheme and make as many notes as possible in order to calmly and without errors re-install the connecting wires and jumpers.

The ohmmeter should show infinity. However, it shows zero (or very low resistance), which no doubt means that there is a possibility of a short circuit between the two windings.
Such a check is less significant for a single-phase motor with an auxiliary winding in case the two windings cannot be separated (when the common point C connecting the two windings is inside the motor). Indeed, depending on exact location finding a short circuit, resistance measurements carried out between the three terminals (C -> A, C -> P and P -> A) give reduced, but rather unrelated values. For example, the resistance between points A and P may not correspond to the sum of the resistances C -> A + C -> P.
Also, as in the case of a winding break, in the event of a short circuit between the windings, it is necessary to either replace or rewind the motor.

The winding can be shorted to ground. The insulation resistance of a new motor (between each winding and ground) must be 1000 MQ. Over time, this resistance decreases and can drop to 10...100 MQ. As a rule, it is considered that starting from 1 MQ (1000 kQ) it is necessary to provide for the replacement of the motor, and with an insulation resistance value of 500 kQ and below, the operation of the motor is not allowed (recall: 1 MQ = 103kQ = 10°>Q).
The winding is shorted to ground
Resistance tends to zero
If the insulation is broken, measuring the resistance between the winding terminal and the motor case gives zero ham (or very low resistance) instead of infinity (see figure 53.8). Note that such a measurement must be made on each motor terminal using the most accurate ohmmeter. Before each measurement, make sure that your ohmmeter is in good condition and that its clamps make good contact with the terminal and metal of the motor housing (if necessary, scrape off the paint on the housing to ensure good contact).
In the example in fig. 53.8 measurement indicates that the winding can certainly be closed to the housing.
Rice. 53.8.
However, the contact of the winding with the mass may not be complete. Indeed, the insulation resistance between the windings and the case can become low enough when the motor is energized to cause the circuit breaker to operate, while remaining high enough that, in the absence of voltage, it cannot be detected with an ordinary ohmmeter.
In this case, it is necessary to use a megger (or similar device) that allows you to monitor the insulation resistance using a constant voltage of 500 V, instead of a few volts for a conventional ohmmeter
When the manual inductor of the megger is rotated, if the insulation resistance is normal, the arrow of the device should deviate to the left (pos. 1) and indicate infinity (oo). A weaker deviation, for example, at the level of 10 MQ (pos. 2), indicates a decrease in the insulating characteristics of the motor, which, although not enough to cause the circuit breaker to trip, nevertheless must be noted and eliminated , because even minor damage to the insulation, in addition to the existing ones, in most cases, sooner or later will lead to a complete stop of the unit.
We also note that only a megohmmeter can make it possible to perform a qualitative check of the insulation of two windings between them when it is impossible to separate them (see above the problem of a short circuit between the windings in a single-phase motor). In conclusion, we point out that the check of a suspicious electric motor must be carried out very strictly.
In any case, it is not enough just to replace the engine, but it is also necessary to find, in addition to this, the root cause of the malfunction (mechanical, electrical or other) in order to radically exclude any possibility of its recurrence. In refrigeration compressors, where there is a high probability of acid in the working fluid (detected by a simple oil analysis), after replacing a burnt out motor, it will be necessary to take measures to additional measures precautions. Do not neglect the inspection of electrical equipment (if necessary, replacing the contactor and breaker, checking connections and fuses ...).

In addition to this, the replacement of the compressor requires highly qualified personnel and strict adherence to the rules: draining the refrigerant, if necessary, flushing the circuit after that, possible installation suction line anti-acid filter, changing the drier filter, looking for leaks, dehydrating the circuit by vacuum, charging the circuit with refrigerant and full control functioning... Finally, especially if the unit was originally charged with CFC type refrigerant (R12, R502...), would it be possible and reasonable to use a compressor change to change the type of refrigerant?
B) Capacitors
To start a single-phase motor with an auxiliary winding, it is necessary to provide a phase shift alternating current in the auxiliary winding in relation to the main one. To achieve a phase shift and, consequently, to ensure the required starting torque (recall that the starting torque of the motor must necessarily be greater than the resistance moment on its shaft), they mainly use capacitors installed in series with the auxiliary winding. From now on, we must remember that if the capacitance of the capacitor is chosen incorrectly (too small or too large), the phase shift achieved may not ensure the start of the engine (the engine stops).
In electrical equipment refrigeration units we will be dealing with two types of capacitors:
Working (running) capacitors (paper) of small capacity (rarely more than 30 microfarads), and of considerable size.
Starting capacitors (electrolytic), which, on the contrary, have a large capacity (may exceed 100 microfarads) with relatively small sizes. They should not be constantly energized, otherwise such capacitors overheat very quickly and may explode. As a rule, it is considered that the time they are energized should not exceed 5 seconds, and the maximum allowable number of starts is no more than 20 per hour.
On the one hand, the dimensions of capacitors depend on their capacitance (the larger the capacitance, the larger the dimensions). The capacitance is indicated on the capacitor case in microfarads (dr, or uF, or MF, or MFD, depending on the developer) with the manufacturer's tolerance, for example: 15uF ± 10% (capacitance can be from 13.5 to 16.5 uF) or 88 -108 MFD (capacitance is 88 to 108uF).
In addition, the dimensions of the capacitor depend on the amount of voltage indicated on it (the higher the voltage, the larger the capacitor). It is useful to recall that the voltage specified by the designer is the maximum voltage that can be applied to the capacitor without fear of destruction. So, if 20 microfarad / 360V is indicated on the capacitor, this means that such a capacitor can be freely used in a network with a voltage of 220 V, but in no case should a voltage of 380 V be applied to it.

Try for each of the 5 capacitors shown in fig. 53.10 on the same scale, determine which of them are working (running) and which are starting.

Capacitor number 1 is the largest of all presented, has a rather low capacitance in comparison with its size. Apparently, this is a working capacitor.
Capacitors No. 3 and No. 4, with the same dimensions, have very small capacity(Note that Capacitor #4, designed for use on a network with a supply voltage higher than Capacitor #3, has a lower capacitance). Therefore, these two capacitors are also working.
Capacitor number 2 has, in comparison with its size, a very large capacitance, therefore it is a starting capacitor. Capacitor #5 has a slightly smaller capacitance than #2, but it's designed for higher voltage: it's also a start capacitor.

Checking capacitors. Measurements with an ohmmeter, when they give the results we have just considered, are an excellent indication of the health of the capacitor. However, they must be supplemented by measuring the actual capacitance of the capacitor (we will see how to make such a measurement shortly).
Now let's study typical faults capacitors (open circuit, short circuit between plates, short to ground, low capacitance) and how to detect them. First of all, it should be noted that swelling of the capacitor case is completely unacceptable.

The capacitor may have an open circuit.
Then an ohmmeter connected to the terminals and set to the maximum range constantly shows infinity. With such a malfunction, everything happens as in the absence of a capacitor. However, if the motor is equipped with a capacitor, then it is needed for something. Therefore, we can imagine that the motor will either not run normally or will not start, which will often cause the thermal protection to trip (thermal protection relay, circuit breaker ...).
There may be a short circuit between the plates inside the capacitor.
With such a fault, the ohmmeter will show zero or very low resistance (use a small range). Sometimes the compressor may start (we'll see why later), but in most cases a short circuit in the capacitor causes the thermal protection to trip.
Plates can be grounded
The plates of the capacitor, as well as the windings of the electric motor, are isolated from the ground. If the insulation resistance drops sharply (the danger of which is manifested by excessive overheating), the leakage current causes the installation to turn off the circuit breaker.
Such a malfunction may occur if the capacitor has a metal sheath. The resistance measured between one of the pins and the body in this case tends to 0, instead of being infinite (you need to check both pins).
Capacitor capacitance may be reduced
In this case, the actual value of the capacitance measured at its ends is lower than the capacitance indicated on the body, taking into account the manufacturer's tolerance.

The measured capacitance would have to be between 90 and 110 microfarads. Therefore, in fact, the capacitance is too low, which will not provide the required amounts of phase shift and starting torque. As a result, the engine may no longer start.

Let us now consider how to measure the actual capacitance of a capacitor using a simple circuit that is easily implemented in the conditions of the installation site.
ABOUT
ATTENTION! To eliminate possible dangers, it is necessary to check the capacitor with an ohmmeter before assembling this circuit.
It is enough to connect an externally serviceable capacitor to an alternating current network with a voltage of 220 V and measure the consumed current (of course, in this case, the operating voltage of the capacitor must be at least 220 V).
The circuit must be protected either by a circuit breaker or a fuse with a knife switch. The measurement should be as short as possible (it is dangerous to keep the start capacitor energized for a long time).

At a voltage of 220 V, the actual capacitance of the capacitor (in microfarads) is about 14 times the current drawn (in amps).

For example, you want to check the capacitance of a capacitor (obviously, this is a start capacitor, so the time it is energized must be very short, see Fig. 53.21). Since it indicates that the operating voltage is 240 V, it can be connected to a 220 V network.

If the capacitance marked on the capacitor is 60uF ± 10% (that is, from 54 to 66uF), theoretically it should draw a current of 60 / 14 = 4.3A.
Install an automatic machine or a fuse designed for such a current, connect transformer clamps and set the measuring range on the ammeter, for example, 10 A. Apply voltage to the capacitor, read the ammeter readings and immediately turn off the power.

CAUTION - DANGER! When you measure the capacitance of the starting capacitor, its time under voltage should not exceed 5 seconds (practice shows that with little effort to organize the measurement process, this time is enough to perform the measurement).
In our example, the actual capacitance is about 4.1 x 14 = 57 uF, which means that the capacitor is good, since its capacitance should be between 54 and 66 uF.
If the measured current were, for example, 3 A, the actual capacitance would be 3 x 14 = 42 uF. This value is out of tolerance, hence the capacitor would need to be replaced.

B) Start relays

In most cases (but not always) these relays are connected directly to the compressor using two or three (depending on models) sockets that accept motor winding plugs, preventing possible errors when connecting the relay to the auxiliary and main windings. On the top cover of the relay, as a rule, the following designations are applied:
R / M -> Working (Main) -> Main winding A / S -> Starting (Start) -> Auxiliary winding L Line (Line) -> Mains phase
If the relay is reversed top cover down, you can clearly hear the sound of moving contacts that slide freely.
Therefore, when installing such a relay, it is necessary to strictly maintain its spatial orientation so that the inscription "Top" (Tor) is on top, since if the relay is turned upside down, its normally open contact will be constantly closed.

When checking with an ohmmeter the resistance between the contacts of the current starting relay (in the case of its correct location) between sockets A/S and P/M, as well as between sockets L and A/S, there must be an open circuit (resistance equal to co), since the relay contacts are open when the power is removed.
Between the P/M and L sockets, the resistance is close to 0, corresponding to the resistance of the relay coil, which is wound with thick wire and is designed to pass the inrush current.
You can also test the resistance of the relay upside down. In this case, between sockets A / S and L, instead of infinity, there should be a resistance close to zero.
When mounting the current relay in an inverted position), its contacts will remain permanently closed, which will not allow the starting winding to be turned off. As a result, there is a risk of rapid combustion of the electric motor.

Let us now study the operation of the starting current relay in the circuit shown in the absence of voltage.
As soon as voltage is applied to the circuit, current will flow through the thermal protection relay, the main winding and the relay coil. Since contacts A/S and L are open, the start winding is de-energized and the motor does not start - this causes a sharp increase in current consumption.
An increase in starting current (about five times the nominal value) provides such a voltage drop on the relay coil (between points L and P / M), which becomes sufficient for the core to be drawn into the coil, contacts A / S and L closed and the starting winding turned out to be under tension.

Thanks to the impulse received from the starting winding, the motor starts and as the number of revolutions increases, the current drawn decreases. At the same time, the voltage on the relay coil drops (between L and P / M). When the motor reaches about 80% of the rated speed, the voltage between points L and P / M will not be enough to keep the core inside the coil, the contact between A / S and L will open and completely disconnect the starting winding.
However, with such a scheme, the starting torque on the motor shaft is very small, since it does not have a starting capacitor that provides a sufficient phase shift between the current in the main and starting windings (recall that the main purpose of the capacitor is to increase the starting torque). That's why this scheme used only in small motors with negligible torque on the shaft.
If we are talking about small refrigeration compressors, in which capillary tubes are necessarily used as an expansion device, ensuring equalization of the pressure in the condenser and the pressure in the evaporator during stops, then the engine starts at the lowest possible moment of resistance on the shaft (see section 51 . "Capillary expansion devices").
If it is necessary to increase the starting torque, a starting capacitor (Cd) must be installed in series with the starting winding. Therefore, current relays are often produced with four sockets, as, for example, in the model presented.
Relays of this type are supplied with a shunt jumper between slots 1 and 2. If a start capacitor is required, the shunt must be removed.
Note that when such a relay rings with an ohmmeter between sockets M and 2, the resistance will be close to zero and equal to the resistance of the relay winding. Between sockets 1 and S, the resistance is equal to infinity (when the relay is in the normal position) and zero (when the relay is turned upside down).

ATTENTION! When replacing a faulty current relay, the new relay must always have the same index as the faulty one.

Indeed, there are dozens of different modifications of the current relay, each of which has its own characteristics (closing and opening current, maximum allowable current ...). If the newly installed relay has different characteristics from the relay being replaced, then either its contacts will never close, or they will remain permanently closed.

If the contacts never close, e.g. because the starting current relay is too strong (designed to close at 12 A inrush current, when in fact the inrush current does not exceed 8 A), the auxiliary winding cannot be energized. and the motor won't start. It hums and is turned off by a thermal protection relay.
Note that the same symptoms accompany such a malfunction as a breakdown of the relay contacts
IN last resort, you can test this hypothesis by short-circuiting contacts 1 and S for a few seconds, for example. If the motor starts, this will be evidence of a relay failure.
If the contact remains constantly closed, for example, due to the low power of the starting current relay (it should open when the current drops to 4 A, and the motor consumes 6 A in nominal mode), the starting winding will be energized all the time. Note that the same will happen if, due to excessive current, the relay contacts are "welded" or if the relay is installed upside down*, causing the contacts to remain permanently closed.
The compressor will then consume a huge current and, in the best case, will be switched off by the thermal protection relay (in the worst case, it will burn out). If at the same time a starting capacitor is present in the circuit, it will also be energized all the time and will overheat strongly with each attempt to start, which will ultimately lead to its destruction.

The normal operation of the starting current relay can be easily checked using transformer clamps installed in the line of the capacitor and the starting winding. If the relay is working properly, then at the moment of starting the current will be maximum, and when the contact opens, the ammeter will show no current.
Finally, to complete the consideration of the current starting relay, it is necessary to dwell on one malfunction that can occur when the condensing pressure rises excessively. Indeed, any increase in the condensing pressure, no matter what it is caused by (for example, the condenser is dirty), inevitably leads to an increase in the current consumed by the motor (see section 10. "Influence of the condensing pressure on the current consumed by the compressor electric motor"). This rise can sometimes be enough to cause the relay to trip and close the contacts while the motor is spinning. You can imagine the consequences of such a phenomenon!
* Installing the start relay in a horizontal plane usually gives the same result and is also incorrect. - Ed.

When the motor power increases (becoming higher than 600 W), the current consumed also increases, and the use of a current starting relay becomes impossible due to the fact that the required diameter of the relay coil increases. The starting voltage relay also has a coil and contacts, but unlike the current relay, the coil of the voltage relay has a very high resistance (it is wound thin wire with a large number of turns), and its contacts are normally closed. Therefore, the probability of confusing these two devices is very small.
presented appearance the most common starting voltage relay, which is a sealed black box. If you ring the relay terminals with an ohmmeter, you can find that between terminals 1 and 2 the resistance is 0, and between 1-5 and 2-5 it is the same and amounts to, for example, 8500 Ohms (note that terminals 4 are not included in the circuit and are used only for ease of connection and wiring on the relay housing).

The relay contacts are probably located between terminals 1 and 2, since the resistance between them is zero, but which of these terminals is connected to one of the coil terminals cannot be determined, since the measurement result will be the same (see the diagram in Fig. 53.29).
If you have a relay circuit, there will be no problems with determining the common point. Otherwise, you will need to perform an additional little experiment, that is, first apply power to terminals 1 and 5, and then 2 and 5 (the resistance measured between them was 8500 ohms, therefore, one of the ends of the coil is connected either to terminal 1 or to terminal 2).

Suppose that when voltage is applied to terminals 1-5, the relay will operate in the "bounce" mode (like a buzzer) and you can clearly distinguish the constant closing and opening of its contact (imagine the consequences of such a mode for the engine). This will be a sign that terminal 2 is common and one of the ends of the coil is connected to it. When
you can test yourself by applying power to terminals 5 and 2 (pins 1 and 2
open and stay open).
ATTENTION! If you apply voltage to terminals 1 and 2 (normally closed contact terminals), you will get a short circuit, which can be very dangerous

To perform this test, you must use 220V if the relay is designed to power a 220V motor (it is highly recommended to use a fuse in the circuit to protect the circuit from possible errors when connected). However, it may happen that the relay contacts will not open either when power is applied to terminals 1 and 5, or when power is applied to terminals 2 and 5, although the coil will be serviceable (when dialing with an ohmmeter, the resistance 1-5 and 2-5 are equally high) . This may be due to the very principle underlying the operation of the circuit with a voltage relay (immediately after this paragraph, we will consider it), which requires an increased voltage relay to operate. To continue the test, you can increase the voltage to 380 V (the relay is not in danger, since it can withstand voltage up to 400 V).

As soon as the circuit is energized, current flows through the thermal protection relay and the main winding (C->P). At the same time, it passes through the starting winding (C-»A). normally closed contacts 2-1 and start capacitor (Cd). All conditions for starting are met and the motor starts to rotate.
As the motor picks up speed, additional voltage is induced in the starting winding, which is added to the supply voltage.

At the end of the start, the induced voltage becomes maximum and the voltage at the ends of the starting winding can reach 400 V (with a supply voltage of 220 V). The voltage relay coil is designed in such a way as to open the contacts exactly at the moment when the voltage on it exceeds the supply voltage by an amount determined by the motor designer. When the contacts I-2 open, the relay coil remains powered by the voltage induced in the starting winding (this winding, wound on the main winding, is, as it were, the secondary winding of the transformer).
During starting, it is very important that the voltage at the relay terminals exactly matches the voltage at the ends of the starting winding. Therefore, the starting capacitor should always be included in the circuit between points I and P, and not between A and 2. Note that when contacts 1-2 are opened, the starting capacitor is completely excluded from the circuit.
There are many different models of voltage relays, differing in their characteristics (contact opening and closing voltage...).

Therefore, if it is necessary to replace a faulty voltage relay, a relay of the same model must be used for this.
If the replacement relay does not quite match the engine, this means that either its contacts will not be closed at start-up or will be closed permanently.
When the relay contacts turn out to be open at startup, for example, due to the fact that the relay is too low-power (it operates at 130 V, that is, immediately after voltage is applied and the starting winding is powered only as secondary winding), the engine will not be able to start, it will hum and be turned off by the thermal protection relay (see Fig. 53.33).

Note that the same signs will occur in the event of a contact breakage. As a last resort, you can always test this hypothesis by briefly shorting contacts 1 and 2. If the engine starts, then there is no contact.

Thermistor Trigger (CTP)

The thermistor, or thermistor (STR * - abbreviation, translated means a positive temperature coefficient, that is, an increase in resistance with increasing temperature) is included in the circuit as shown in fig. 53.37.
When the motor rotor is stationary, the STR is cold (has ambient temperature) and its resistance is very low (a few ohms). As soon as voltage is applied to the motor, the main winding is energized. Simultaneously, current passes through the low resistance of the CTP and the start winding, causing the motor to start. However, the current flowing through the starting winding, passing through the STR, heats it, which causes a sharp increase in its temperature, and hence the resistance. After one or two seconds, the temperature of the CTP becomes more than 100°C, and its resistance easily exceeds 1000 ohms.
A sharp increase in the resistance of the CTP reduces the current in the starting winding to a few milliamps, which is equivalent to turning off this winding in the same way as a conventional starting relay would. A weak current, without any effect on the state of the starting winding, continues to pass through the STR, remaining quite sufficient to maintain its temperature at the desired level.
This method of starting is used by some designers if the moment of resistance at start is very small, for example in installations with capillary expansion devices (where pressure equalization is unavoidable upon shutdown).
However, once the compressor has stopped, the stop time should be long enough to not only equalize the pressures, but also to cool down the CTP mainly (calculated to take at least 5 minutes).
Any attempt to start the motor with a hot CTP (hence very high resistance) will prevent the starting winding from starting the motor. For such an attempt, you can pay a significant increase in current and the operation of a thermal protection relay.
Thermistors are ceramic discs or rods and the main failure mode of this type of starters is their cracking and destruction of internal contacts, most often caused by attempts to start at hot GTP, which
inevitably entails an excessive increase in the starting current.
. We have often pointed out the importance of respecting the identity of models when replacing faulty items of electrical equipment ( thermal relays protection, starting relays...) to new ones, or to those that are recommended for replacement by the developer. We also recommend changing the starter kit (relay + capacitor(s)) when replacing the compressor.
* Sometimes the term RTS is encountered, which means the same as STR (note peo.j.

D) Generalization of the most common schemes of starting devices

In the documentation of various developers, there are many schemes with several exotic names which we will now explain. Taking this opportunity, we will replenish our knowledge and see the role of working capacitors.
For better understanding For further material, we recall that, unlike starting capacitors, running capacitors are designed to be constantly energized and that the capacitor is included in the circuit in series with the starting winding, allowing you to increase the torque per motor shaft.
1) PSC circuit (Permanent Split Capacitor) - the circuit with a permanently connected capacitor is the simplest, since it does not have a start relay.
A capacitor, constantly under voltage (see Fig. 53.40 \ must be a working capacitor. Since this type of capacitor quickly increases in size with increasing capacitance, their capacitance is limited to small values ​​\u200b\u200b(rarely more than 30 microfarads).
Therefore, the PSC scheme is used, as a rule, in small motors with low shaft torque (small refrigeration compressors for capillary expansion devices that provide pressure equalization during shutdowns, fan motors of small air conditioners).
When voltage is applied to the circuit, a permanently connected con-
the condenser (Cp) gives a push, allowing the engine to start. When the motor is started, the start winding remains energized along with the capacitor in series, which limits the current and allows for more torque when the motor is running.
2) Scheme PAGE previously studied, is also called PTC (Positive Temperature Coefficient) and is used as a relatively simple trigger.
It can be improved by adding a permanently connected capacitor.
When voltage is applied to the circuit (after a stop of at least 5 minutes), the resistance of the thermistor CTP is very low and the capacitor Cp, being short-circuited, does not affect the start process (therefore, the moment of resistance on the shaft should be insignificant, which requires equalization of pressures when stopping ).
At the end of the start-up, the resistance of the STR increases sharply, but the auxiliary winding remains connected to the network through the capacitor Cp, which allows you to increase the torque when the engine is running (for example, with an increase in condensation pressure).
Since the capacitor is energized all the time,
starting capacitors in circuits of this type cannot be used.

A single-phase motor with a supply voltage of 220 V, equipped with a 3 microfarad run capacitor, rotates the air conditioner fan. The switch has 4 terminals: "Input" (V), "Low speed" (MS), "Medium speed" (SS), "High speed" (BS), allowing you to switch the motor with the network in such a way as to select the required value (MS , SS or BS) speed.

Solution

Let's sketch, according to our assumption, the internal circuit of the engine, referring to the resistance measurement data (for example, between Г and Ж there should be 290 Ohms, and between Г and 3 - 200 Ohms).
It remains only to include a switch in the circuit, remembering that maximum speed rotation (BS) is achieved if the motor is directly connected to the network. And vice versa, the minimum number of revolutions will be provided at the weakest supply voltage, therefore, when using the maximum value of the damping resistance.

Such motors, which are currently rare, can however be used to drive gland compressors. To change the direction of rotation of the motor, it is enough to crosswise change the connection point of the starting and main windings.
As an example, in fig. it is shown how the end of the starting winding became the beginning, and the beginning became the end.
Note that in this case, the direction of current flow through the starting winding has changed to the opposite, which allows you to give an impulse at the moment of starting magnetic field in the opposite direction.
Finally, we also note two-wire "Fraget" or "phase-shifting ring" motors, widely used to drive small fans with low resistance torque (usually bladed). These motors are very reliable, although they have low torque, and there are no particular problems when they are connected to the network, since they have only two wires (plus earth, of course).

B) Start relays
Regardless of the design, the task of the start relay is to turn off the start winding as soon as the motor reaches approximately 80% of the rated speed. After that, the engine is considered to be started and continues to rotate only with the help of a working winding.
There are two main types of start relays: current relay and voltage relay. We will also mention triggering with the thermistor PP.
First, we will study the starting current relay
This type of relay is generally used in small single-phase motors used to drive compressors with a power not exceeding 600W (domestic refrigerators, small freezers...).

Instruction

Examine the engine carefully. In the event that it has six pins with jumpers, check in what order they are installed. If the engine has six leads and no block, the leads must be collected in two bundles, and the beginnings of the windings should be collected in one bundle, and the ends in the second.

In the event that the engine has only three leads, disassemble the motor: remove the cover from the block side and find the connection of three wires in the windings. Then disconnect these three wires from each other, solder lead wires to them and combine them into a bundle. Subsequently, these six wires will be connected in a "triangle" pattern.

Calculate the approximate capacitance of the capacitor. To do this, substitute the values ​​​​in the formula: Cmkf \u003d P / 10, in which Cmkf is the capacitance of one capacitor in microfarads, P is the rated power (in watts). And here's what else is important: the operating voltage of the capacitor must be high.

Please note: if you turn on the volt capacitors in a serial way of connecting, then half of the capacitance will be “lost”, but the voltage will double. A battery of the required capacity can be assembled from a pair of such capacitors.

When connecting capacitors, take into account their peculiarity: the fact is that after disconnecting the capacitors, they retain voltage at the terminals for a long time. In view of this, such capacitors pose a danger to life, because the risk of electric shock is too high.

The starting resistance Rn is determined empirically. To increase the torque during engine start, connect the starting capacitor simultaneously with the working capacitor (it is connected in parallel with the working one). Calculate the capacitance of the starting capacitor using the formula: Sp \u003d (from 2.5 to 3) Cp, in which Cp is the capacitance of the working capacitor.

Capacitors are actively used in the automotive industry in high-tech electrical equipment. They are included in many components and mechanisms of the car, starting from the control unit power plant, ending with the power supply circuits of the audio system.

Instruction

Without a capacitor, stable operation of the power supply is impossible. It must be included in wiring diagram, in addition, have a certain capacity. This part, in fact, dampens voltage drops in the electrical network, as a shock absorber does, smoothing out the bumps in the road. At the same time, it accumulates excess electricity and gives it away as needed. This protects the elements from burnout and wear. Which capacitor is recommended for your car is usually indicated in the documentation for it. If the documents are lost, contact a specialized car service.

Choosing the right capacitor for you is an important task. After all, this market is developing dynamically, provoking developers and manufacturers to release new models. And the number of manufacturers is constantly growing. However, everything

home » Electrical equipment » Electric motors » Single-phase » How to connect a single-phase electric motor through a capacitor: starting, working and mixed switching options

How to connect a single-phase electric motor through a capacitor: starting, working and mixed switching options

In technology, asynchronous motors are often used. Such units are characterized by simplicity, good performance, low noise level, ease of operation. In order to asynchronous motor rotated, a rotating magnetic field is required.

Such a field is easily created if there is three-phase network. In this case, in the motor stator, it is enough to place three windings placed at an angle of 120 degrees from each other and connect the appropriate voltage to them. And the circular rotating field will begin to rotate the stator.

However Appliances commonly used in homes that most often have only single-phase electrical network. In this case, single-phase asynchronous motors are usually used.

Why is it used to start a single-phase motor through a capacitor?

If one winding is placed on the motor stator, then during the flow of alternating sinusoidal current it generates a pulsating magnetic field. But this field will not be able to make the rotor rotate. To start the engine you need:

• place an additional winding on the stator at an angle of about 90 ° relative to the working winding;
• in series with an additional winding, turn on a phase-shifting element, for example, a capacitor.

In this case, a circular magnetic field will appear in the motor, and currents will appear in the squirrel-cage rotor.

The interaction of currents and the stator field will lead to the rotation of the rotor. It is worth recalling that to adjust the starting currents - control and limitation of their magnitude - use a frequency converter for asynchronous motors.

Switching scheme options - which method to choose?

• launcher,
• workers,
• start and run capacitors.

The most common method is the scheme with starting capacitor .

In this case, the capacitor and the starting winding are turned on only at the moment the engine starts. This is due to the property of the unit continuing its rotation even after turning off additional winding. For such inclusion, a button or relay is most often used.

Since the start-up of a single-phase motor with a capacitor occurs quite quickly, the additional winding works for a short time. This allows, for economy, to make it from a wire with a smaller cross section than the main winding. To prevent overheating of the additional winding, a centrifugal switch or thermal relay is often added to the circuit. These devices turn it off when the engine picks up a certain speed or when it gets very hot.

The start capacitor circuit has good motor starting characteristics. But performance is degraded with this inclusion.

This is due to the principle of operation of an asynchronous motor. when the rotating field is not circular, but elliptical. As a result of this field distortion, losses increase and efficiency decreases.

There are several options for connecting asynchronous motors to operating voltage. Star and delta connections (as well as the combined method) have their advantages and disadvantages. The selected switching method affects the starting characteristics of the unit and its operating power.

Operating principle magnetic starter It is based on the appearance of a magnetic field when electricity passes through a retracting coil. Read more about motor control with and without reversing in a separate article.

Better performance can be obtained by using a circuit with working capacitor .

In this circuit, the capacitor does not turn off after the engine starts. The right selection capacitor for a single-phase motor, you can compensate for field distortion and increase the efficiency of the unit. But for such a circuit, starting characteristics deteriorate.

It must also be taken into account that the choice of the capacitor capacitance for a single-phase motor is made for a certain load current.

When the current changes relative to the calculated value, the field will change from a circular to an elliptical shape and the performance of the unit will deteriorate. Basically, to ensure good performance it is necessary to change the value of the capacitance of the capacitor when the engine load changes. But this can complicate the wiring diagram too much.



A compromise solution is to choose a scheme with start and run capacitors. For such a circuit, the operating and starting characteristics will be average compared to the previously considered circuits.

In general, if a large starting torque is required when connecting a single-phase motor through a capacitor, then a circuit with a starting element is selected, and if there is no such need, with a working one.

Connection of capacitors for starting single-phase electric motors

Before connecting to the engine, you can check the capacitor with a multimeter for operability.

When choosing a scheme, the user always has the opportunity to choose exactly the scheme that suits him. Typically, all winding leads and capacitor leads are routed to the motor terminal box.

The presence of three-core wiring in a private house involves the use of a grounding system. which you can do by hand. How to replace the wiring in the apartment typical schemes, can be found here.

If necessary, you can upgrade the circuit or independently calculate the capacitor for a single-phase motor, based on the fact that for each kilowatt of power of the unit, a capacitance of 0.7 - 0.8 microfarads is required for the working type and two and a half times more capacitance for the starting one.

When choosing a capacitor, it must be taken into account that the starting one must have an operating voltage of at least 400 V.

This is due to the fact that when starting and stopping the engine in electrical circuit due to the presence EMF self-induction there is a surge of voltage, reaching 300-600 V.

1. Single-phase asynchronous motor is widely used in household appliances.
2. To start such a unit, an additional (starting) winding and a phase-shifting element - a capacitor are required.
3. Exist various schemes connecting a single-phase electric motor through a capacitor.
4. If more starting torque is needed, a start capacitor circuit is used, if good motor performance is required, a run capacitor circuit is used.