How to check an electric motor with a multimeter: step by step instructions and recommendations. How to check an electric motor: dialing with a tester and other methods How to properly check a three-phase motor with a multimeter

/ 27.07.2018

How to check an electric motor

You can detect a malfunction with uneven heating of the tool body. Touching with your hand, you feel the temperature difference in different parts of the case. In this case, the tool must be disassembled and checked with a tester and other methods.

In the event of a short circuit of the stator turns and troubleshooting, first of all we inspect the turns and leads. As a rule, during a short circuit, the current passing through the windings increases, and their overheating occurs.

There is a greater short circuit of the turns in the stator windings and the insulation layer is damaged. Therefore, we begin to identify faults by conducting a visual inspection. If burns and damaged insulation are not found, then proceed to the next step.

Perhaps the cause of the breakdown is a malfunction of the voltage regulator that occurs when the excitation currents increase. To detect a problem, the brushes are checked, they must be ground evenly and not chipped or damaged. Then you should check with a light bulb and 2 batteries.

Multimeter application

Now we need to check the possibility of breaking the stator windings. On the multimeter scale, set the switch to the sector for measuring resistance. Without knowing the measurement value, we set the maximum value for your device. We check the performance of the tester.

We touch each other with probes. The arrow of the device should show 0. We carry out work by touching the terminals of the windings. When an infinite value is shown on the multimeter scale, the winding is faulty and the stator should be rewound.

We check the possibility of a short circuit to the case. Such a malfunction will cause a decrease in the power of the grinder, the possibility of electric shock and an increase in temperature during operation. The work is carried out according to the same scheme. We turn on the resistance measurement on the scale.

We place the red probe on the winding terminal, we attach the black probe to the stator housing. If the winding is short-circuited to the case on the tester scale, the resistance value will be less than on a good one. This fault requires rewinding of the stator windings.

It is time to take measurements and check if there is an interturn short circuit in the stator winding. To do this, the resistance value on each winding is measured. We determine the zero point of the windings by measuring the resistance for each of them. When the winding resistance is shown on the device, it should be changed.

Checking the motor windings

The electronic rotor tester is a standard digital multimeter. Before you start testing the circuit, you should check the multimeter and its readiness for operation. The switch is set to measure resistance and the probes touch each other. The instrument should show zeros. Set the maximum measurement value and check:

This completes the rotor test. It is necessary to recall once again the main stages of troubleshooting. Before checking, the grinder or any other device should be de-energized. Before taking measurements, you should visually inspect the housings, insulation and the absence of deposits on the stator and rotor.

It is necessary to clean the contact surfaces from blockages with dust and dirt. Pollution leads to an increase in current when the motor power is lost.

When disassembling an instrument for the first time, write down all your steps. This will allow you to have a hint next time, to avoid the appearance of unnecessary parts during assembly. If the brush goes beyond the edge of the brush holder less than 5 mm, such brushes should be replaced. You can check the interturn circuit with an electronic tester, that is, a multimeter.

Checking the electric motor by external inspection

A full inspection can be carried out only after disassembling the electric motor, but do not rush to disassemble immediately.

All work is carried out only after turning off the power supply, checking its absence on the electric motor and taking measures to prevent its spontaneous or erroneous switching on. If the device is plugged into an outlet, then just remove the plug from it.

If there are capacitors in the circuit. then their conclusions must be discharged.

Check before starting disassembly:

1. play in bearings. How to check and replace bearings read in this article.
2. Check the paint coverage on the body. Burnt or peeling paint in places indicates engine heating in these places. Pay special attention to the location of the bearings.
3. Check the motor mounting feet and the shaft together with its connection to the mechanism. Cracks or broken legs must be welded.

After disassembling according to this instruction, you need to check:

It may burn out as part of the winding and an interturn circuit will occur (in the picture on the left), and the entire winding (in the right picture). Despite the fact that in the first case the motor will run and overheat, it is still necessary to rewind the windings in any case.

How to ring an asynchronous electric motor

If nothing is revealed during the external examination, then it is necessary to continue the check using electrical measurements.

How to ring an electric motor with a multimeter

The most common electrical measuring device in the household is a multimeter. With its help, you can ring the integrity of the winding and the absence of a breakdown on the case.

In 220 volt motors. It is necessary to ring the starting and working windings. Moreover, the starting resistance will be 1.5 times greater than that of the working one. For some electric motors, the starting and working windings will have a common third terminal. Read more about this here.

For example. the motor from the old washing machine has three outputs. The greatest resistance will be between two points, including 2 windings, for example 50 ohms. If you take the remaining third end, then this will be the common end. If you measure between it and the 2nd end of the starting winding, you will get a value of about 30-35 ohms, and if between it and the 2nd end of the working winding, about 15 ohms.

In 380 volt motors connected according to the star or delta circuit, it will be necessary to disassemble the circuit and ring each of the three windings separately. Their resistance should be the same from 2 to 15 ohms with deviations of no more than 5 percent.

It is imperative to ring all the windings between themselves and on the case. If the resistance is not great to infinity, then there is a breakdown of the windings between themselves or on the case. Such motors must be put into winding rewinding.

How to check the insulation resistance of the motor windings

Unfortunately, it is not possible to check the insulation resistance value of the motor windings with a multimeter; for this, a 1000-volt megger with a separate power source is required. The device is expensive, but every electrician at work who has to connect or repair electric motors has it.

When measuring, one wire from the megohmmeter is connected to the body in an unpainted place, and the second in turn to each winding terminal. Then measure the insulation resistance between all windings. If the value is less than 0.5 Megoma, the engine must be dried.

Be careful. To avoid electric shock, do not touch the test clamps during measurements.

All measurements are carried out only on de-energized equipment and for a duration of at least 2-3 minutes.

How to find an interturn circuit

The most difficult is the search for an interturn circuit. at which only a part of the turns of one winding is closed to each other. It is not always detected during an external examination, therefore, for these purposes, it is used for 380 Volt motors - an inductance meter. All three windings must have the same value. With an interturn circuit, the damaged winding will have a minimum inductance.

When I was in practice 16 years ago at the plant, electricians used a bearing ball with a diameter of about 10 millimeters to search for turn-to-turn short circuits in a 10 kilowatt asynchronous motor. They took out the rotor and connected 3 phases through 3 step-down transformers to the stator windings. If everything is in order, the ball moves in a circle of the stator, and in the presence of an interturn short circuit, it is magnetized to the place of its occurrence. The check should be short-term and be careful the ball can fly out!

I've been an electrician for a long time and I check for turn-to-turn shorts, unless a 380V motor starts to get very hot after 15-30 minutes of operation. But before disassembling, with the motor turned on, I check the amount of current it consumes in all three phases. It should be the same with a slight correction for measurement errors.

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Interturn short circuit of the electric motor

Causes of interturn circuit

If you have read previous articles, you know that the turn-to-turn short circuit of an electric motor accounts for 40% of electric motor failures. There can be several reasons for an interturn short circuit.

Electric motor overload - the load on the electrical installation exceeds the norm, as a result of which the stator windings heat up and the insulation of the windings is destroyed, which leads to an interturn short circuit. The load may arise due to improper operation of the equipment. The rated load can be determined from the passport of the electrical installation or read on the nameplate of the electric motor. Also, overload can occur due to mechanical damage to the electric motor itself. Seized or dry bearings can also cause inter-turn "short".

The possibility of a factory defective windings is not ruled out, and if the electric motor was rewound in a handicraft workshop, then there is a high probability that the “mezhvitnyak” is already knocking on your door.

Also, improper operation and storage of the electric motor can cause moisture to get inside the motor. Damp windings are also a very common cause of interturn short circuit.

As a rule, with such a short circuit, the electric motor is no longer a tenant, and it will work for a very short time. I think it's enough to analyze the reasons, let's move on to the question "how to determine the interturn short circuit."

Search for an interturn circuit.

Determining the turn-to-turn short is not too difficult, and there are several handy ways to do this.

If during the operation of the electric motor some part of the stator has heated up more than the entire engine, then you should think about stopping and accurate diagnosis.

Ordinary current clamps will also help to determine the short circuit, we measure the load on each phase in turn, and if on one of them it is greater than on the others, then this is a sign that there may be an interturn winding. But it should be borne in mind that there may be a phase imbalance at the substation in order to make sure that the incoming voltage is measured with a voltmeter.

You can ring the windings with a tester. To do this, we call each winding separately and compare the results of the resistance. This method may not work if only a couple of turns are closed, then the discrepancy will be minimal.

It will not be superfluous to blurt out the electric motor with a megohmmeter in search of a short to the case, we apply one probe to the motor case, and the second to in turn to the output of the windings in boron.

If you still have doubts, then you will have to disassemble the electric motor. Having removed the covers and the rotor, we visually examine the windings. It is likely that you will see a burnt part.

Well, the most accurate way to check the turn-to-turn circuit is to check with a three-phase step-down transformer (36-42 volts) and a ball from a bearing.

We supply three phases from a step-down transformer to the starter of the disassembled electric motor. With a small acceleration, we throw a ball there, if the ball starts to run in a circle inside the stator, then everything is in order. If he, having made a couple of turns, stuck to one place, then there is an inter-turn short circuit.

Instead of a ball, you can use a plate from transformer iron, put it inside the stator to the iron and in the place where the interturn it will begin to rattle, and where everything is in order, the plate will be magnetized.

Be sure to use all of the above methods with a grounded motor and strictly with a step-down transformer.

Testing with a ball and plate at a voltage of 380 volts is prohibited and very dangerous for your life.

Winding insulation resistance measurement

To test the motor for insulation resistance, electricians use a megger with a test voltage of 500 V or 1000 V. This device measures the insulation resistance of motor windings rated for an operating voltage of 220 V or 380 V.

For electric motors with a rated voltage of 12V, 24V, a tester is used, since the insulation of these windings is not designed for testing with a high voltage of 500V megger. Usually, the test voltage is indicated in the passport for the electric motor when measuring the insulation resistance of the coils.

Insulation resistance is usually checked with a megger

Before measuring the insulation resistance, you need to familiarize yourself with the connection diagram of the electric motor, since some star connections of the windings are connected by a midpoint to the motor housing. If the winding has one or more connection points, "delta", "star", single-phase motor with starting and working winding, then the insulation is checked between any connection point of the windings and the housing.

If the insulation resistance is significantly less than 20 MΩ, the windings are disconnected and checked each separately. For a whole motor, the insulation resistance between the coils and the metal case must be at least 20 MΩ. If the motor has been operated or stored in damp conditions, then the insulation resistance may be below 20 MΩ.

Then the electric motor is disassembled and dried for several hours with a 60 W incandescent lamp placed in the stator housing. When measuring insulation resistance with a multimeter, set the measurement limit to the maximum resistance, to megohms.

How to ring an electric motor for a winding break and an interturn short circuit

The turn-to-turn short circuit in the windings can be checked with a multimeter on ohms. If there are three windings, then it is enough to compare their resistance. The difference in the resistance of one winding indicates an interturn short circuit. The turn-to-turn short circuit of single-phase motors is more difficult to determine, since there are only different windings - this is the starting and working winding, which has less resistance.

There is no way to compare them. It is possible to identify the interturn short circuit of the windings of three-phase and single-phase motors with measuring clamps, comparing the winding currents with their passport data. With an interturn circuit in the windings, their rated current increases, and the starting torque decreases, the engine starts with difficulty or does not start at all, but only buzzes.

Checking the motor for open circuit and interturn circuit of the windings

It will not work to measure the resistance of the windings of powerful electric motors with a multimeter, because the cross section of the wires is large and the resistance of the windings is within tenths of an ohm. It is not possible to determine the difference in resistance, with such values ​​​​with a multimeter. In this case, the health of the electric motor is best checked with current clamps.

If it is not possible to connect the electric motor to the network, the winding resistance can be found by an indirect method. A series circuit is assembled from a 12V battery with a 20 ohm rheostat. Using a multimeter (ammeter), a current of 0.5 - 1 A is set with a rheostat. The assembled device is connected to the winding under test and the voltage drop is measured.

Electric motor continuity and insulation resistance

A smaller voltage drop across the coil will indicate an interturn short circuit. If you want to know the resistance of the winding, it is calculated by the formula R \u003d U / I. A motor failure can also be determined visually, on a disassembled stator, or by the smell of burnt insulation. If the place of the break is visually detected, it can be eliminated, the jumper soldered, well insulated and laid.

The measurement of the winding resistance of three-phase motors is carried out without removing the jumpers on the connection diagrams of the "star" and "delta" windings. The resistance of the coils of collector electric motors of direct and alternating voltage is also checked with a multimeter. And with their high power, the check is carried out using the accumulator - rheostat device, as indicated above.

The winding resistance of these motors is checked separately on the stator and rotor. On the rotor, it is better to check the resistance directly on the brushes by turning the rotor. In this case, it is possible to determine the loose fit of the brushes to the rotor lamellae. Eliminate carbon deposits and irregularities on the collector lamellas by grinding them on a lathe.

It is difficult to do this operation manually, you can not eliminate this malfunction, and the sparking of the brushes will only increase. The grooves between the lamellas are also cleaned. In the windings of electric motors, a fuse, a thermal relay can be installed. If there is a thermal relay, check its contacts and, if necessary, clean them.

The main malfunctions of the electric motor

Every year, gasoline engines are increasingly being replaced by electric motors installed in a new type of car called electric vehicles. However, just like internal combustion engines, electric powertrains can break down, causing problems in vehicle operation. The bulk of electric motor malfunctions occur due to severe wear of mechanism parts and aging of materials, which is supported by improper operation of such a car. There can be many reasons for the appearance of characteristic problems, and we will now tell you about some (the most common) ones.

Causes of motor failure

All possible malfunctions of the electric vehicle engine can be divided into mechanical and electrical. The causes of mechanical problems include distortions of the electric motor housing and its individual parts, loosening of fasteners and damage to the surface of the constituent elements or their shape. In addition, overheating of bearings, oil leakage and abnormal operating noise are common problems. The most typical malfunctions of the electrical part are attributed to short circuits inside the windings of the electric motor, as well as between them, short circuits of the windings to the housing and breaks in the windings or in the external circuit, that is, in the supply wires and starting equipment.

As a result of the appearance of certain malfunctions, the following malfunctions may occur in the operation of the vehicle: the impossibility of starting the motor, dangerous heating of the windings, abnormal motor speed, unnatural noise (hum or knock), unequal current strength in individual phases.

Typical motor problems

Let's look at the breakdowns of electric motors in more detail, identifying their possible causes.

AC motor

Problem: when connected to the power supply, the electric motor does not develop the rated speed and makes unnatural sounds, and when the shaft is scrolled by hand, uneven operation is observed. The reason for this behavior is most likely a break in two phases when the stator windings are connected in a triangle, or a break when connected in a star.

If the motor rotor does not rotate, emits a strong hum and heats up above the permissible level, it can be said with confidence that the stator phase failure is to blame. When the engine hums (especially when trying to start), and the rotor rotates at least slowly, but often the cause of the problem is a break in the phase of the rotor.

It happens that with a rated load on the shaft, the electric motor works stably, but its rotational speed is somewhat less than the rated one, and the current in one of the stator phases is increased. As a rule, this is a consequence of a break in the phase when the windings are connected in a triangle.

If at idle speed of the electric motor there are local overheating of the stator active steel, this means that due to damage to the intersheet insulation or burnout of the teeth due to damage to the winding, the sheets of the stator core are closed to each other.

When the stator winding overheats in separate places, when the motor cannot develop the rated torque and hums strongly, the cause of this phenomenon should be sought in the turn circuit of one phase of the stator winding or interphase circuit in the windings.

If the entire motor overheats evenly, then the fan of the ventilation system is faulty, and overheating of plain bearings with ring lubrication is due to one-sided attraction of the rotors (due to excessive wear of the liner) or poor fit of the shaft to the liner. When a rolling bearing overheats, making abnormal noise, it is likely that the reason for this lies in the contamination of the lubricant, excessive wear of the rolling elements and raceways, or inaccurate alignment of the shafts of the unit.

Knocking in the plain bearing and in the rolling bearing is due to serious wear of the liner or destruction of the tracks and rolling elements, and increased vibration is a consequence of the imbalance of the rotor due to interaction with pulleys and couplings, or the result of inaccurate alignment of the shafts of the unit and misalignment of the connecting halves.

A DC motor can also have its own characteristic malfunctions:

Under a serious load, the armature of the machine may not rotate, and if you try to turn it around with an external force, the engine will run “out of order”. Causes: poor contact or complete open circuit of the excitation circuit, interturn or short circuits inside the independent excitation winding. Under the conditions of the nominal values ​​of the mains voltage and excitation current, the armature speed may be less or more than the established norm. In this case, the culprits for this situation are the brushes shifted from the neutral position in the direction of rotation of the shaft or against it.

It may also be that the brushes of one sign spark a little more than the brushes of another sign. It is possible that the distances between the rows of brushes are not the same along the circumference of the collector, or there is an interturn short circuit in the windings of one of the main or additional "pluses". If the blackening of the collector plates, which are located at a certain distance from each other, is also added to the sparking of the brushes, then the culprit of this situation is most likely a poor contact or short circuit in the armature winding. Also, do not forget about the possibility of a break in the armature coil attached to the blackened plates.

In cases where only every second or third collector plate darkens, the cause of the malfunction may be a weakened pressing of the collector or a protruding micanite of insulating tracks. Brushes can spark even with normal heating of the motor and a fully functional brush apparatus, which is explained by unacceptable wear of the collector.

The reasons for the increased sparking of the brushes, overheating of the collector and the darkening of most of it are usually insulation tracks (they say that the collector “beats”). When the motor armature rotates in different directions, the brushes also spark with different intensity. There is only one reason - the displacement of the brushes from the central.

If there is an increased sparking of the brushes on the collector, then it is worth checking the tightness of their fit, as well as diagnosing for defects in the working surface of the brushes. In addition, the reason may lie in the unequal pressure of the brushes or in their jamming in the brush holder. Naturally, if any of the listed problems is detected, it must be correctly eliminated, but quite often only highly qualified specialists can do this.

Troubleshooting the motor

High-quality overhaul of electric motors can only be carried out at specialized enterprises. During the current repair work, the power unit is disassembled and the subsequent partial replacement of worn parts is carried out. Let's look at the order in which all actions are performed using the example of an asynchronous electric motor.

At the initial stage, using a screw puller, a pulley or half-coupling is removed from the motor pulley. After that, you need to unscrew the bolts securing the fan casing and remove it. Further, using the same screw puller, you need to unscrew the locking screw and remove the fan itself. If necessary, the same tool can be used to remove the bearings from the motor shaft, and then, by unscrewing the mounting bolts, dismantle their covers as well.

After that, unscrew the bolts securing the bearing shields and remove these shields with light blows of a hammer through a wooden gasket. In order not to damage the steel and the windings, a cardboard spacer is placed in the air gap, on which the rotor is lowered. The assembly of the electric motor is carried out in the reverse order.

After performing repair work (the specifics of the performance depend on the nature of the breakdown), the electric motor should be tested. To do this, simply turn the rotor by holding the pulley, and if the assembly is done correctly, the unit should rotate easily. If everything is fine, the engine is installed in place, connected to the network and checked for operability in idle mode, after which the motor is connected to the machine shaft and tested again. Let's look at the options for troubleshooting an electric motor using some typical breakdowns as an example.

So, let's imagine that the motor does not start due to a lack of voltage in the network, a shutdown of the machine, or blown fuses. The presence of voltage can be checked using a special device - an AC voltmeter with a scale of 500 V, or using a low-voltage indicator. You can fix the problem by replacing blown fuses. Note! If at least one fuse blows, the engine will emit a characteristic hum.

An open phase of the stator winding can be detected with a megger, but before that, all ends of the motor windings must be released. If a break is detected inside the winding phase, then the motor will have to be sent for professional repair. The permissible rate of voltage drop at the motor terminals when it is started is considered to be an indicator of 30% of the nominal value, which is due to losses in the network, insufficient power of the transformer or its overload.

If you notice a decrease in voltage at the terminals of the electric motor, it is necessary to replace the supply transformer or increase the cross section of the supply line wires. The absence of a power supply contact in one of the stator windings (phase loss) causes an increase in current in the element windings and a decrease in the number of revolutions. If you leave the motor running on two windings, it will simply burn out.

In addition to the listed electrical problems, electric motors can also suffer from mechanical problems. So, the cause of excessive heating of the bearings is often the incorrect assembly of these parts, poor alignment of the motor, contamination of the bearings, or excessive wear of the balls and rollers.

In any case, before proceeding to direct action, a complete diagnosis of the electric motor and the parts interacting with it should be carried out. The inspection procedure begins with checking the battery, and if it is in good condition, then the next step is to check the supply of power to the controller circuit (ECU that controls the speed of rotation of the electric motor). It is quite possible that on the way from the battery to the board you will find a wire break. Breakdown of an electronic board is an infrequent phenomenon, but if there is even the slightest doubt about its serviceability, then it is better to immediately visually assess the condition of the part. If there was a strong heating of the board elements, you will immediately find blackened and swollen areas with possible smudges.

In the event that the car owner has at least minimal knowledge in the field of electronics, he can independently check the fuses, semiconductor parts (like diodes and transistors), all contacts, capacitances and soldering quality.

When, in the on state, there is an operating voltage at the output of the computer, then, as a rule, the cause of the malfunction should be sought in the electric motor itself. The complexity of repairing the unit depends on the specific malfunction and type of mechanism. So, when examining rotary-fed AC motors, first of all, it is necessary to check the contact brushes, because they are the most often the cause of breakdowns of engines of this type. After that, the windings should be checked for an open or short circuit. In the event of a break, the tester will not show any resistance value, and in the event of a short circuit, the resistance indicator will correspond to zero or one Ohm.

Having found a malfunction, it, of course, must be eliminated. This can be done either by repairing and replacing failed parts (for example, brushes), or by replacing the entire motor with a working analogue.

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Methods for diagnosing malfunctions of asynchronous electric motors

The engine does not turn over when starting, or the rotation speed is abnormal. The causes of this malfunction can be mechanical and electrical problems.

Electrical problems include: internal breaks in the stator or rotor winding, break in the mains supply, disruption of normal connections in the starting equipment. If the stator winding breaks, a rotating magnetic field will not be created in it, and if there is a break in two phases of the rotor, there will be no current in the winding of the latter interacting with the rotating stator field, and the engine will not be able to work. If a winding break occurs while the motor is running, it may continue to operate at rated torque, but the rotation speed will be greatly reduced, and the current will increase so much that, in the absence of maximum protection, the stator or rotor winding may burn out.

If the motor windings are connected into a triangle and one of its phases is interrupted, the motor will start to turn around, since its windings will be connected into an open triangle, in which a rotating magnetic field is formed, the current strength in the phases will be uneven, and the rotation speed will be lower than the nominal one. With this fault, the current in one of the phases in the case of a rated motor load will be 1.73 times greater than in the other two. When all six ends of its windings are removed from the engine, a phase break is determined with a megohmmeter. The winding is disconnected and the resistance of each phase is measured.

The motor rotation speed at full load below the nominal may be due to low mains voltage, poor contacts in the rotor winding, and also due to high resistance in the rotor circuit of a motor with a phase rotor. With a large resistance in the rotor circuit, the motor slip increases and its rotation speed decreases.

The resistance in the rotor circuit is increased by poor contacts in the rotor brush device, starting rheostat, winding connections with slip rings, soldering of the frontal parts of the winding, as well as insufficient cross-section of cables and wires between slip rings and starting rheostat.

Bad contacts in the rotor winding can be detected if a voltage equal to 20-25% of the nominal voltage is applied to the motor stator. The locked rotor is slowly turned by hand and the current strength is checked in all three phases of the stator. If the rotor is in good condition, then at all its positions the current in the stator is the same, and in the event of a break or poor contact, it will vary depending on the position of the rotor.

Bad contacts in the soldering of the frontal parts of the phase rotor winding are determined by the voltage drop method. The method is based on increasing the voltage drop in places of poor-quality soldering. At the same time, the magnitude of the voltage drop is measured at all joints, after which the measurement results are compared. Solders are considered satisfactory if the voltage drop in them exceeds the voltage drop in the solderings with minimum values ​​by no more than 10%.

Rotor with deep slots can also break the bars due to mechanical overstressing of the material. The rupture of the rods in the slot part of the squirrel-cage rotor is determined as follows. The rotor is pulled out of the stator and several wooden wedges are hammered into the gap between them so that the rotor cannot turn. A reduced voltage of not more than 0.25 Unom is applied to the stator. A steel plate is alternately placed on each groove of the protruding part of the rotor, which should cover two teeth of the rotor. If the rods are intact, the plate will be attracted to the rotor and rattle. In the presence of a gap, the attraction and rattling of the plate disappear.

The motor turns around with the phase rotor open circuit. The cause of the malfunction is a short circuit in the rotor winding. When turned on, the motor slowly turns around, and its windings become very hot, since a large current is induced in the short-circuited turns by the rotating stator field. Short circuits occur between the clamps of the frontal parts, as well as between the rods during breakdown or weakening of the insulation in the rotor winding.

This damage is determined by careful visual inspection and measurement of the insulation resistance of the rotor winding. If during the inspection it is not possible to detect damage, then it is determined by the uneven heating of the rotor winding to the touch, for which the rotor is braked, and a reduced voltage is supplied to the stator.

Uniform heating of the entire engine above the permissible norm can result from prolonged overload and deterioration of cooling conditions. Increased heat causes premature wear of the winding insulation.

Local heating of the stator winding, which is usually accompanied by a strong buzz, a decrease in the motor speed and uneven currents in its phases, as well as the smell of overheated insulation. This malfunction can occur as a result of incorrect connection of the coils in one of the phases, a short circuit of the winding to the housing in two places, a short circuit between two phases, a short circuit between the turns in one of the phases of the stator winding.

In case of short circuits in the motor windings, e will be induced by a rotating magnetic field in a short-circuited circuit. d.s., which will create a large current, depending on the resistance of the closed circuit. A damaged winding can be found by the value of the measured resistance, while the damaged phase will have less resistance than the good ones. Resistance is measured by a bridge or by the method of an ammeter - voltmeter. A damaged phase can also be determined by measuring the current in the phases if a reduced voltage is applied to the motor.

When the windings are connected to a star, the current in the damaged phase will be greater than in the others. If the windings are connected in a delta, the line current in the two wires to which the damaged phase is connected will be greater than in the third wire. When determining the specified damage for a motor with a squirrel-cage rotor, the latter may be inhibited or rotate, and for motors with a phase rotor, the rotor winding may be open. Damaged coils are determined by the voltage drop at their ends: on damaged coils, the voltage drop will be less than on serviceable ones.

Local heating of the active steel of the stator occurs due to burnout and melting of the steel during short circuits in the stator winding, as well as when the steel sheets are closed due to the rotor touching the stator during engine operation or due to the destruction of the insulation between individual steel sheets. Signs of grazing the rotor on the stator are smoke, sparks and the smell of burning; active steel in the places of grazing takes the form of a polished surface; there is a hum, accompanied by engine vibration. The reason for grabbing is a violation of the normal gap between the rotor and the stator as a result of bearing wear, improper installation, large shaft bending, deformation of the stator or rotor steel, one-sided attraction of the rotor to the stator due to turn short circuits in the stator winding, strong vibration of the rotor, which determined with a probe.

Abnormal noise in the engine. A normally running motor produces a uniform hum that is common to all AC machines. An increase in hum and the appearance of abnormal noises in the engine may be the result of a weakening of the active steel pressing, the packages of which will periodically shrink and weaken under the influence of a magnetic flux. To eliminate the defect, it is necessary to repress the steel packages. Strong buzz and noises in the machine can also be the result of an uneven gap between the rotor and the stator.

Damage to the winding insulation can occur from prolonged overheating of the motor, moistening and contamination of the windings, metal dust, shavings on them, and also as a result of natural aging of the insulation. Insulation damage can cause short circuits between phases and turns of individual winding coils, as well as short circuit windings on the motor housing.

Moistening of the windings occurs in the event of long interruptions in the operation of the engine, with direct ingress of water or steam into it as a result of storing the engine in a damp, unheated room, etc.

Metal dust that gets inside the machine creates conductive bridges, which can gradually cause short circuits between the phases of the windings and to the housing. It is necessary to strictly observe the terms of inspections and scheduled preventive repairs of engines.

The insulation resistance of the motor windings with voltage up to 1000 V is not standardized, the insulation is considered satisfactory with a resistance of 1000 ohms per 1 V of the rated voltage, but not less than 0.5 MΩ at the operating temperature of the windings.

The short circuit of the winding on the motor housing is detected with a megohmmeter, and the place of the short circuit is detected by the method of “burning” the winding or by supplying it with direct current.

The “burning” method consists in the fact that one end of the damaged phase of the winding is connected to the network, and the other to the case. When the current passes in the place where the winding is shorted to the case, a “burn-through” is formed, smoke and the smell of burnt insulation appear.

The engine does not start as a result of blown fuses in the armature winding, a break in the resistance winding in the starting rheostat, or a broken contact in the supply wires. A break in the resistance winding in the starting rheostat is detected with a test lamp or a megohmmeter.

Today we will discuss how to ring an electric motor with a multimeter. A screwdriver-indicator is suitable for those who know how to use it. One caveat: with the help of a tester, we will evaluate the parameters, distinguish the starting winding from the working winding by the resistance value (in the first case, the value will be twice as high). The indicator screwdriver is miniature, convenient, you will acquire the ability to use it, if necessary, by paying 30 rubles you will find a new one.

Motor device

There are many types of engines. Composed by a moving part - a rotor - a fixed part - a stator. First of all, let's see where the copper wire is wound. There are three answer options:

1. Coils on the rotor only.
2. Coils on the stator only.
3. On the movable and fixed parts of the winding.

Otherwise, ringing an asynchronous electric motor will be no more difficult than a collector one. And vice versa. The difference is limited to the principle of operation, without affecting the methodology for assessing the performance of the structure. To correctly ring the electric motor, stop disassembling the features.

Motor rotor

In this and the next subheading, we will teach you how to ring a three-phase electric motor. If there are coils (regardless of the number) on the rotor, we look at the design of the current collector. There are at least two answers.

Graphite brushes

We see the rotor drum, equipped with pronounced sections. Current collectors are graphite brushes. Collector motor. You need to ring all sections. The coil leads are opposite sections of the circle.

We take a tester, we begin to evaluate the resistance one by one: in each case, the answer (in ohms) is the same plus or minus the error. When fixing a break, cleaning the drum does not help. The fact of infinite resistance or short circuit indicates: the coil burned out. In some engines, the coil resistance is close to zero.

They told me what to do in this case. Take a normal Krona 12 volts, connect the rotor coil in series with a low-resistance resistance (20 ohms). Using a tester, measure the voltage drop across the coil, additional resistor, using the proportion, calculate the value (R1 / R2 \u003d U1 / U2). Please note that the resistor is high-precision (E48 series or higher), so that the calculations have a small error. It is possible to measure relatively small resistances.

Please note: the current reaches 0.5A at a power of 7W. Instead of a battery, it is better to take a computer power supply or a battery.

Continuous rings

The current collector is made in the form of one or more continuous rings. It indicates eloquently: a synchronous motor (the number of phases by the number of sections), or an asynchronous motor with a phase rotor. Actually, this is not the case, because we were going to ring the electric motor with a tester, we will be too lazy to determine the purpose of the device. We look at the number of rings: the number fits within the limits of 1 - 3. The latter means: a three-phase motor. We start calling.

The windings are connected in a star, as a result, the resistance between each two contacts is equal. If you have equipment on hand to create a voltage of 500 V, you should ring the electric motor with a megohmmeter on the case. The standard insulation value is 20 MΩ. Please note: windings may not pass the test. With a 12 volt motor, such actions should not be taken. As a result, with a fully serviceable rotor, equal resistance will be obtained between the contacts. If a short to ground is detected, check if it is a technical solution to create a system with a solidly grounded neutral.

It's time to mention that for such a system, the power supply method is typical for voltages below 1 kV. However, with resonant compensation (if it is possible to find an engine in nature), something similar can be used. On the nameplate with the marking, you can quickly resolve the issue (neutral output to the housing).

Collector brushes are more often located perpendicular to the surface of the drum, while they are pressed against the current collectors at a certain angle. The question arises - where is the neutral. Does not go to the body - do not use in the circuit. Often found at voltages above 3 kV. Here the neutral is isolated, the currents go through the phase, where in this case there is zero (or a negative value).

In high voltage circuits, the common wire can be grounded through the arcing reactor. When one phase is short-circuited to ground, a parallel circuit is formed between the line capacitance and the reactor inductance. Actually, the type of impedance gave the name to the device (the imaginary, reactive part of the resistance). At industrial frequency, the resistance of the circuit is close to infinity, as a result, the break is blocked until the arrival of the repair team.

The rotor is often referred to as the armature.

motor stator

After calling the rotor of the electric motor, take care of the stator. Detail of a simpler design. If we have a generator in front of us, part of the exciting windings, in the general case, you just need to find the resistance of each. Windings are starting only single-phase circuits. The coil resistance will be higher. Let's say there are three contacts, then the distribution between them is as follows:

• The common wire of both windings, where zero (ground) is applied.
• Phase input of the working coil.
• The end of the starting winding, where 230 volts is supplied, bypassing the capacitor.

The difference is made according to the resistance value: the value between the phase inputs is greater, therefore, the remaining end is the neutral wire. Further division is carried out as described above. The resistance of the starting coil is the largest (the difference between zero and this contact), the remaining ends will indicate the working winding. The value of the active part of the impedance is reduced, reducing thermal losses. Please note: there are also models of electric motors for 230 volts, where both windings are considered to be working. The difference in resistance between them is small (less than two times).

For three-phase motors, the stator windings are made for a different number of poles, always equivalent. Strict symmetry is practiced. The association is carried out according to the star scheme. In high power collector motors, additional (additional) ones can be placed between the poles of the main coil. They are wound in one layer, therefore they show more resistance. Designed to compensate for the reactive power of the armature. It is clear that the number of additional poles is equal to the number of main ones. The difference is limited by geometric dimensions.

The core of the additional poles is made with an overlap (laminated design) to reduce eddy currents. Similar to the rotor, it will not be enough to ring a three-phase electric motor with a multimeter, you should also measure the insulation of the case (typical value 20 MΩ).

Additional engine design

Often the composition of engines is replete with additional elements that optimize the work, performing a protective, different function. Varistors should be included here. Resistors connecting each brush to the body, with a sharp increase in voltage, close the spark. Extinguishing is in progress. Phenomena such as circular fire on the collector lead to premature equipment failure.

The phenomenon is observed as a result of the occurrence of back-EMF. The generation mechanism is quite simple: when the current changes in the conductor, a force is formed that counteracts the process. In the process of moving to the next section, the phenomenon causes the appearance of a potential difference between the brush and the non-working part of the collector. At voltages above 35 volts, the process causes ionization of the gap air, which is observed in the form of a spark. At the same time, the noise characteristics of the equipment deteriorate.

This phenomenon, however, is used to monitor the constancy of the speed of rotation of the shaft of the collector motor. The level of sparking is determined by the number of revolutions. When the parameter deviates from the nominal, the thyristor circuit changes the voltage cutoff angle in the desired direction in order to return the shaft speed to the nominal one. Such electronic boards are often found in household food processors or meat grinders. The composition of the engine is as follows:

Electrical engine

1. Thermal fuses. The response temperature is chosen to protect the insulation from burnout and destruction. The fuse is fixed on the motor housing with a steel shackle, or is hidden under the winding insulation. In the latter case, the conclusions stick out, you can easily ring with a multimeter. It is easier to trace, with the help of a tester, an indicator screwdriver, which pins of the connector the protection circuit goes to. In the normal state, the thermal fuse gives a short circuit.
2. Temperature relays are installed instead of frequency fuses. Normally open or closed. The latter type is more commonly used. A brand is written on the body, you can find the corresponding type of element on the Internet. Then proceed according to the information found (type, resistance, response temperature, position of the contacts at the initial moment of time).
3. On the engines of washing machines, speed sensors and tachometers are often installed. In the first case there are three conclusions, in the second - two. The principle of operation of Hall sensors is based on a change in the potential difference in the transverse direction of the plate, through which a weak electric current flows. Accordingly, the two extreme outputs are used to supply power, they should give a short circuit (small resistance), while the output can only be checked under the influence of a magnetic field in operating mode. To do this, you need to supply power according to the electrical wiring. We recommend downloading the technical information (data sheet) for the Hall sensor present in the electric motor. Other options have been devised. You can measure the power with a tester while the washing machine is on. We believe readers understand the dangers of manipulation. It would be better to remove the electric motor, supply power separately, only to the Hall sensor. Then it all depends on the design. If the magnet is permanent on the rotor, it is enough just to rotate the axis by hand so that pulses appear at the output of the Hall sensor (fixed by the tester). Otherwise, you will need to remove the sensor. Enlisting the help of a permanent magnet, the performance is checked. The Hall sensor as part of the electric motor is usually used to control the speed of rotation.

Now readers know how to ring an electric motor with a multimeter, the review ends. A number of specific devices can be continued indefinitely. The main thing is to ring the motor winding, the motor usually costs more than other parts. We do not take the case when the Hall sensor is priced at 4,000 rubles. We are sure that readers will be able to supplement the recommendations. But enter into a position - it is impossible to embrace the immensity ... within one review.

The electric motor is the main component of any modern household electrical equipment, whether it is a refrigerator, vacuum cleaner or other unit used in the household. In the event of a failure of any device, it is first necessary to establish the cause of the failure. To find out if the motor is in good condition, it must be checked. It is not necessary to carry the device to the workshop for this, it is enough to have an ordinary tester. After reading this article, you will learn how to check the electric motor with a multimeter, and you can handle this task yourself.

What electric motors can be checked with a multimeter?

There are various modifications of electric motors, and the list of their possible malfunctions is quite large. Most problems can be diagnosed using a regular multimeter, even if you are not an expert in this field.

Modern electric motors are divided into several types, which are listed below:

• Asynchronous, three-phase, with a squirrel-cage rotor. This type of electric powertrain is the most popular due to its simple device that provides easy diagnostics.
• Asynchronous capacitor, with one or two phases and squirrel-cage rotor. Such a power plant is usually equipped with household appliances powered by a conventional 220V network, the most common in modern homes.
• Asynchronous, equipped with a phase rotor. This equipment has a more powerful starting torque than motors with a squirrel-cage rotor, and therefore it is used as a drive in large power devices (hoists, cranes, power plants).
• Collector, direct current. Such motors are widely used in automobiles, where they play the role of driving fans and pumps, as well as power windows and wipers.
• Collector, alternating current. These motors are equipped with hand-held power tools.

The first step in any diagnosis is a visual inspection. Even if burnt windings or broken parts of the motor are visible to the naked eye, it is clear that further verification is pointless, and the unit must be taken to the workshop. But often an inspection is not enough to identify problems, and then a more thorough check is necessary.

Repair of asynchronous motors

The most common asynchronous power units for two and three phases. The order of their diagnosis is not exactly the same, so we should dwell on this in more detail.

Three phase motor

There are two types of malfunctions of electrical units, regardless of their complexity: the presence of contact in the wrong place or its absence.

A three-phase AC motor consists of three coils that can be connected in a delta or star configuration. There are three factors that determine the performance of this power plant:

• Correct winding.
• The quality of the insulation.
• Reliability of contacts.

A short to the case is usually checked with a megohmmeter, but if it is not there, you can get by with an ordinary tester by setting the maximum resistance value on it - megaohms. In this case, one cannot speak of high measurement accuracy, but it is possible to obtain approximate data.

Before measuring the resistance, make sure that the motor is not connected to the mains, otherwise the multimeter will become unusable. Then you need to calibrate by setting the arrow to zero (the probes must be closed). It is necessary to check the serviceability of the tester and the correctness of the settings by briefly touching one probe to the other every time before measuring the resistance value.

Attach one probe to the motor housing and check that there is contact. After that, take the readings of the device, touching the engine with the second probe. If the data is within the normal range, connect the second probe to the output of each phase in turn. A high resistance value (500-1000 or more MΩ) indicates good insulation.

How to check the insulation of the windings is shown in this video:

Then you need to make sure that all three windings are intact. You can check this by ringing the ends that go into the motor terminal box. If a break in any winding is detected, the diagnostics should be stopped until the malfunction is corrected.

The next check point is the determination of short-circuited turns. Quite often, this can be seen during a visual inspection, but if the windings look normal on the outside, then you can establish the fact of a short circuit by unequal current consumption.

Two phase electric motor b

Diagnostics of power units of this type is somewhat different from the above procedure. When checking a motor equipped with two coils and powered by a conventional electrical network, its windings must be ringed with an ohmmeter. The resistance index of the working winding should be 50% less than that of the starting winding.

Be sure to measure the resistance to the case - normally it should be very large, as in the previous case. A low resistance indicator indicates the need to rewind the stator. Of course, to obtain accurate data, it is better to carry out such measurements with a megohmmeter, but such an opportunity at home is rarely available.

Checking collector electric motors

Having dealt with the diagnostics of asynchronous motors, let's move on to the question of how to ring the electric motor with a multimeter if the power unit is of the collector type, and what are the features of such checks.

To correctly check the performance of these engines with a multimeter, you need to proceed in the following order:

• Turn on the ohm tester and measure the resistance of the collector lamellas in pairs. Normally, these data should not differ.
• Measure the resistance indicator by attaching one probe of the device to the armature body, and the other to the collector. This indicator should be very high, tend to infinity.
• Check the stator winding for continuity.
• Measure the resistance by applying one probe to the stator housing and the other to the terminals. The higher the score, the better.

Checking the motor with a multimeter for an interturn short circuit will not work. For this, a special apparatus is used, with the help of which the anchor is checked.

A detailed check of power tool motors is shown in this video:

Features of checking electric motors with additional elements

Often, electric power plants are equipped with additional components designed to protect equipment or optimize its operation. The most common elements built into the motor are:

An ordinary multimeter is usually sufficient to diagnose most of the problems that can occur in electric motors. If it is not possible to establish the cause of the malfunction with this device, the check is carried out using high-precision and expensive devices that only specialists have.

This material contains all the necessary information on how to properly check the electric motor with a multimeter at home. When any electrical equipment fails, the most important thing is to ring the motor winding in order to exclude its malfunction, since the power plant has the highest cost compared to other elements.

Setting up DC motors

The adjustment of constant current engines is done in the following volume: external inspection, measurement of winding resistance to constant current, measurement of the insulation resistance of the windings relative to the housing and among themselves, testing of the inter-turn insulation of the armature winding, test run.

An external inspection of a DC motor, as well as an inspection of an asynchronous motor, begins with a shield. On the shield DC motor current, the following data must be indicated:

• name or trademark of the manufacturer,

• machine type,

• machine serial number,

• nominal data (power, voltage, current, speed),

• machine excitation method,

• year of issue,

• weight and GOST of the machine.

Motor winding leads direct current must be firmly isolated from each other and from the body, the distance between them and the body must be more than 12-15 mm. During external examination, increased attention is paid to the collector and the brush mechanism (brushes, traverse and brush holders), because their condition significantly affects the switching of the machine, and, as it should, the stability of its operation.

When inspecting the collector, make sure that there are no traces of a cutter, potholes, varnish and paint stains on the working surface, as well as traces of soot from the unsatisfactory operation of the brush mechanism. The insulation between the collector plates should be selected to a depth of 1-2 mm, a chamfer 0.5-1 mm wide should be removed from the edges of the plates (depending on the motor power). The gaps between the plates must be completely clean - they should not contain iron shavings or sawdust, dust from graphite brushes, oil, varnish, etc.

The operation of the DC motor, and in particular its brush mechanism, is affected by the beating of the collector and its vibration. The higher the circumferential speed of the collector, the smaller the amount of allowable runout. For high-speed engines, the maximum allowable runout value should not exceed 0.02-0.025 mm. The magnitude of the vibration amplitude is determined by a dial gauge.

When measuring, the indicator tip is pressed against the surface in the direction in which the vibration measurement is to be made. Because the surface of the collector is interrupted (collector plates and cavities alternate), a well-ground brush is used, against which the tip of the indicator should rest. The indicator housing must be mounted on a base that is not subject to vibration.

When measuring, the indicator needle oscillates with the frequency of the measured vibration within a certain angle, the value of which is estimated on the indicator scale in hundredths of a mm. But this device allows you to determine the vibration at a speed of less than 750 rpm. For engines whose rotational speed exceeds 750 rpm, you need to use special vibration meters or vibrographs that allow you to determine or record the vibration of certain machine components.

The beat is also determined using an indicator. The runout of the collector is determined both in the cool and in the heated state of the machine. When measuring, pay attention to the behavior of the indicator arrow. The smooth movement of the arrow indicates a sufficient cylindricity of the surface, and the twitching of the arrow indicates local violations of the cylindricity of the surface, especially unsafe for the brush mechanism of the motor. The measurement of the beat is conditional, because experience shows that there are engines that have significant beat values ​​at low speeds, and they work satisfactorily at nominal speed. Therefore, the final conclusion about the quality of the collector can be given only after checking the operation of the motor under load.

When inspecting the mechanical part of a DC motor, one should pay attention to the state of soldering and winding connections, bearing assemblies, to the uniformity of the gap (with the engine disassembled). The gap measured at the diametrically opposite points between the armature and the main poles of the motor should not differ from the average value by more than 10% for gaps of less than 3 mm and less than 5% for gaps of more than 3 mm.

After checking the beats and vibrations, they begin to adjust the brush mechanism of the motor. The brushes in the clips should move freely, but should not stagger. The usual gap between the brush and the holder in the direction of rotation should not exceed 0.1-0.4 mm, in the longitudinal direction 0.2-0.5 mm.

The usual specific pressure of brushes on the commutator, depending on the brand of brush material, should be more than 150-180 g/cm2 for graphite brushes, 220-250 g/cm2 for copper-graphite brushes. To avoid uneven current distribution, the pressure of individual brushes should not differ from the average by more than 10%. The value of the specific pressure is determined as follows. A sheet of thin paper is placed between the collector and the brush, a dynamometer is attached to the brush, and then, pulling the brush with the dynamometer, they find a position where it will be possible to freely pull out a sheet of paper. The dynamometer reading at this point corresponds to the brush pressure on the manifold. The specific pressure is determined by dividing the dynamometer reading by the base area of ​​the brush.

Proper installation of the brushes is one of the most important factors for the smooth operation of the machine. The brush holders are installed in such a way that the brushes are strictly parallel to the collector plates and the distances between their running edges are equal to the pole division of the machine with an error of no more than 2%.

For engines with several traverses, the brush holders are placed in such a way that the brushes cover as much of the length of the collector as possible (the so-called staggered arrangement). This will allow you to participate in the commutation of the entire length of the collector, which contributes to its more uniform wear. However, with such an arrangement of the brushes, it is necessary to ensure that the brushes do not protrude during operation (taking into account the run-up of the shaft) beyond the edge of the collector. Before starting the engine, the brushes are carefully ground to the collector (Fig. 1) with glass (but not carborundum) paper with medium-sized grains. Grains of carborundum paper can penetrate into the body of the brush and then scratch the commutator during operation, thereby worsening the commutation conditions of the machine.

how check collector electric motor multimeter - stator and rotor windings

Read also:

electric motor direct current. Principle of operation.

DC motors can be found in many portable home devices, cars.

Before proceeding to check the correctness of the inclusion of the windings, they study the marking of the conclusions of a particular type of machine. In DC motors, the winding leads are marked in accordance with GOST 183-66 with the first capital letters of their name, followed by the number 1 for the beginning of the winding and 2 for its end. If there are other windings of the same name in the engine, their beginnings and ends are marked with the numbers 3-4, 5-6, etc. The terminal designations can correspond to the excitation circuits and directions of rotation of the engine, which are shown in fig. 2.

The correctness of the inclusion of the windings of the poles is checked to clarify the alternation of their polarity. The alternation of the polarity of the additional and main poles for any machine must be strictly defined for a given direction of rotation of the machine. When moving from pole to pole in the direction of rotation of the machine operating in motor mode, each main pole is followed by an additional pole of the same polarity, for example N-p, S-s. The alternation of the polarity of the poles can be determined in several ways: external examination, using a magnetic needle, and using a special coil.

The first method is used in cases where the winding direction of the windings can be traced visually.

Rice. 1. Lapping brushes to the commutator: a - wrong; b - right

Rice. 2. Designations of the terminals of the windings of DC motors for various excitation schemes and directions of rotation

Knowing the winding direction of the winding and using the “gimlet” rule, the polarity of the poles is determined. This method is convenient for coils of a series excitation winding, the winding direction of which, due to the significant cross section of the turns, is very easy to determine.

The second method is used mainly for coils of parallel excitation windings. The essence of this method is as follows. Current is applied to the motor winding, a magnetic needle is suspended on a thread, the polarity of the ends of which is marked, and it is brought in turn to each pole. Depending on the polarity of the pole, the arrow will turn towards it with the end of the opposite polarity.

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When using this method, it must be remembered that the arrow has the ability to re-magic, so the experiment must be done as quickly as possible. The magnetic needle method is rarely used to determine the polarity of a series excitation winding, since a significant current must be passed through the winding to create a sufficiently strong field.

The third way to determine the polarity of the windings is applicable to any winding, it is called the test coil method. The coil can have any shape - torroidal, rectangular, cylindrical. The coil is wound with the largest possible number of turns of thin insulated copper wire on a frame made of cardboard, celluloid, etc. The coil is attached to a sensitive galvanometer and applied to the surface of the pole (Fig. 3), and then quickly pulled off it and the direction of the deflection of the arrow is noted millivoltmeter.

The connection of the windings is considered correct if, under each two adjacent poles, the arrows of the device deviate in different directions, provided that the test coil faces the poles with the same side. Checking the correctness of the connection of the winding of the additional poles in relation to the armature winding is carried out according to the scheme shown in fig. 4.

When the key K is closed, the arrow of the millivoltmeter will deviate. When properly turned on, the magnetizing force of the winding of the additional poles is directed oppositely to the magnetizing force of the armature winding, therefore the armature winding and the winding of the additional poles must be turned on in the opposite direction, i.e. the minus (or plus) of the armature should be connected to the minus (or plus) windings of the additional poles.

Rice. 3. Determining the polarity of the poles of DC motors using a test coil

Rice. 4. Scheme for checking the correctness of the inclusion of the winding of additional poles in relation to the armature winding

To check the mutual inclusion of the winding of additional poles and the compensation winding, you can use the circuit shown in fig. 5, for small engines.

During normal engine operation direct current the magnetic flux created by the compensation winding must coincide in direction with the magnetic flux of the additional pole winding. After determining the polarity of the windings, the compensation winding and the winding of the additional poles must be switched on in concert, i.e., the minus of one winding should be connected to the plus of the other.

Rice. 5. Scheme for checking the correctness of the inclusion of the winding of additional poles to the compensation winding

Before determining the polarity of the brushes and making the necessary measurements of the resistance of the windings, set the brushes to neutral. The neutral of an electric motor is understood as such a mutual arrangement of the windings of the main poles and the armature, when the transformation ratio between them is zero. To install the brushes on the neutral, a circuit is assembled (Fig. 6).

The excitation winding is connected to a power source (battery) through a key, and a sensitive millivoltmeter is connected to the armature brushes. When a current is applied to the excitation winding with a push, the millivoltmeter needle deviates in one direction or another. When the position of the brushes is strictly in the neutral pointer of the device will not deviate.

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The accuracy of conventional instruments is low - at best 0.5%. Therefore, the brushes are set to the position corresponding to the minimum reading of the instrument, and this is considered to be neutral. The difficulty in setting the brushes to neutral is that the position of the neutral depends on the position of the commutator plates.

It often happens that the neutral found for one position of the anchor moves when it is turned. Therefore, the neutral position is determined for two different shaft positions. If the position of the neutral turns out to be different for different positions of the armature, then the brushes should be set in the middle position between the two marks. The accuracy of setting the brushes to neutral depends on the degree of adhesion of the brush surface to the commutator. Therefore, in order to obtain a more accurate result, when determining the neutral of the engine, the brushes are first rubbed against the collector.

The polarity of the brushes is determined by one of the following methods.

1. A voltmeter is connected to two points of the collector (Fig. 7), spaced from opposite brushes at the same distance. When excitation is applied, the voltmeter needle will deviate in one direction or another. If the arrow deviates to the right, then "plus" is at point 1, and "minus" is at point 2. The brush closest against the direction of rotation will have the polarity of the attached appliance clamp.

2. A direct current of a certain polarity is passed through the excitation winding, a voltmeter is connected to the armature and the armature is set into rotation by hand or by means of a mechanism. The voltmeter needle will deviate. The direction of the deflection of the arrow will indicate the polarity of the brushes.

Measuring the resistance of the windings of a DC motor is a very important element in checking DC motors, since the results of the measurement are used to judge the state of the contact connections of the windings (solders, bolted, welded joints). Measuring the resistance of the motor windings is carried out by one of the following methods: ammeter-voltmeter, single or double bridge and microohmmeter. It is necessary to remember some features of measuring the resistance of the windings of DC motors.

1. The resistance of the series excitation winding, equalizing winding, winding of additional poles is small (thousandths of an ohm), therefore, measurements are made with a microohmmeter or a double bridge.

2. The resistance of the armature winding is measured by the ammeter-voltmeter method using a special two-contact probe with springs in the insulating handle (Fig. 8). The measurement is carried out as follows: to the collector plates of the fixed armature with the brushes removed, one by one constant current from a well-charged battery with a voltage of 4-6 V. Between the plates to which the current is supplied, the voltage drop is measured using a millivoltmeter. The desired value of the resistance of one armature branch

Rice. 6. Scheme for checking the correct installation of brushes in neutral

How to check the condition of the electric motor winding

At first glance, the winding is a piece of wire wound in a specific way and there is nothing to break in it. But she has features:

serious selection of homogeneous material along the entire length;

clear calibration of shape and cross section;

applying a layer of varnish in industrial conditions, which has the highest insulating qualities;

strong contacts.

If at any point of the wire any of these requirements is violated, then the conditions for the passage of electronic current change and the engine starts to work with reduced power or stops altogether.

To check one winding of a three-phase motor, you need to disconnect it from other circuits. What electric motors can be checked with a multimeter? Three-phase how to check the insulation. In all electric motors, they can be assembled according to one of 2 schemes:

The ends of the windings are usually brought out to the terminal blocks and marked with the signs "H" (beginning) and "K" (end). How to test an engine with a multimeter. From time to time, individual connections may be hidden inside the case, and other methods of designation are used for terminals, for example, by numbers.

A three-phase motor on the stator uses windings with similar electronic features that have equal resistances. If, when measured with an ohmmeter, they show different values, then this is already a reason to seriously think about the reasons for the scatter in readings.

How do faults appear in the winding

It is not possible to visually assess the quality of the windings due to the limited access to them. In practice, their electronic properties are inspected, taking into account that all winding faults appear:

breakage, when the integrity of the wire is violated and the passage of electronic current through it is excluded;

a small circuit that occurs when the insulation layer between the input and output turns is broken, characterized by the exclusion of the winding from work with shunting of the ends;

interturn short circuit, when the insulation is broken between one or more nearby turns, which are thereby taken out of operation. The current passes through the winding, bypassing the short-circuited turns, without overcoming their electronic resistance and without creating a certain work by them;

insulation breakdown between the winding and the stator or rotor housing.

Checking the winding for a broken wire

This type of malfunction is determined by measuring the insulation resistance with an ohmmeter. The device will show a huge resistance - ∞, which takes into account the section of the air space formed by the gap.

Checking the winding for a short circuit

The engine, inside the electronic circuit of which a short circuit has appeared, is turned off by protection from the power supply. But, even with a quick withdrawal from work by this method, the place where the short circuit appears is clearly visible visually due to the consequences of exposure to high temperatures with pronounced soot or traces of melting of metals.

With electronic methods for determining the resistance of the winding with an ohmmeter, a very small value comes out, very close to zero. Indeed, virtually the entire length of the wire is excluded from the measurement due to random shunting of the input ends.

Checking the winding for an interturn short circuit

This is a more hidden and difficult to detect malfunction. Several methods can be used to identify it.

Ohmmeter method

The device operates on a constant current and measures only the active resistance of the conductor. The winding, when working due to turns, makes a significantly huge inductive component.

When the 1st turn is closed, and their total number can be several hundred, it is very difficult to see the change in active resistance. After all, it varies within the limits of a few percent of the total value, and immediately less.

How to ring an electric motor

three-phase asynchronous electric motor, checking by a tester. In practice, quite check electric motor

The location of the contacts of a three-phase motor and the continuity of the windings

We consider the placement of the ends of the windings three-phase motor, we determine whether they are connected correctly.

You can try to accurately calibrate the device and closely measure the resistance of all windings, comparing the results. But the difference in readings, even in this case, will not always be visible.

More accurate results can be obtained by the bridge method for measuring active resistance, but this is usually a laboratory method that is difficult for most electricians.

Measurement of consumption currents in phases

With an interturn circuit, the ratio of currents in the windings changes, and excessive heating of the stator appears. A good motor has similar currents. Therefore, their direct measurement in the current circuit under load more accurately reflects the real picture of the technical condition.

AC measurements

It is not always possible to find the impedance of the winding, taking into account the inductive component in a complete working circuit. To do this, you have to remove the cover from the terminal box and cut into the wiring.

For a motor that has been taken out of operation, a step-down transformer with a voltmeter and an ammeter can be used for measurement. To limit the current will allow a current-limiting resistor or a rheostat of the corresponding rating.

When measuring, the winding is inside the magnetic circuit, and the rotor or stator can be removed. There will be no balance of electrical flows, on the condition of which the engine is designed. About how to check the engine and can it be trusted with a multimeter? And how can. Therefore, a reduced voltage is used and the values ​​\u200b\u200bof currents are controlled, which should not exceed the nominal values.

The voltage drop measured across the winding divided by the current, according to Ohm's law, will give the value of the impedance. It remains to be compared with the features of other windings.

The same scheme allows you to remove the current-voltage properties of the windings. You just need to take measurements at various currents and write them down in tabular form or build graphs. If, when compared with similar windings, there are no serious deviations, then there is no inter-turn short circuit.

ball in stator

The method is based on the development of a rotating electric field with serviceable windings. How to check an electric motor with a multimeter step by step. To do this, they are supplied with a three-phase symmetrical voltage, but certainly a reduced value. For this purpose, three similar step-down transformers are usually used, operating in each phase of the power circuit.

To limit the current loads on the windings, the experiment is carried out for a short time.

A small metal ball from a ball bearing is introduced into the rotating magnetic field of the stator immediately after the coils are energized. If the windings are in good order, then the ball rolls synchronously along the inner surface of the magnetic circuit.

When one of the windings has an interturn circuit, the ball will hang at the fault.

During the test, the current in the windings must not exceed the nominal value and it should be taken into account that the ball freely jumps out of the body at the speed of departure from the slingshot.

Electrical check of winding polarity

The stator windings may not be marked at the beginning and end of the leads and this will make correct assembly more difficult.

In practice, 2 methods are used to search for polarity:

1. using a low-power constant current source and a sensitive ammeter showing the direction of the current;

2. by using a step-down transformer and a voltmeter.

In both versions, the stator is considered as a magnetic circuit with windings, operating by analogy with a voltage transformer.

Polarity check with battery and ammeter

On the outer surface of the stator, three separate windings are brought out by six wires, the beginnings and ends of which must be found.

With the help of an ohmmeter, they call and mark the conclusions related to each winding, for example, with the numbers 1, 2, 3. Then they arbitrarily mark the beginning and end on any of the windings. An ammeter is connected to one of the remaining windings with an arrow in the center of the scale capable of indicating the direction of the current.

The minus of the battery is aggressively connected to the end of the selected winding, and the plus is briefly touched at its beginning and immediately breaks the circuit.

When a current pulse is applied to the first winding, it is transformed due to electric induction into a second circuit closed through the ammeter, repeating its original shape. In this case, if the polarity of the windings is guessed correctly, then the ammeter needle will deviate to the right at the beginning of the pulse and move to the left when the circuit is opened.

If the arrow behaves differently, then the polarity is simply confused. It remains only to mark the conclusions of the 2nd winding.

Another 3rd winding is checked in the same way.

Polarity check with step-down transformer and voltmeter

Here, too, the windings are first called with an ohmmeter, determining the conclusions that relate to them.

Then, the ends of the first selected winding are arbitrarily marked for connection to a step-down voltage transformer, for example, 12 volts.

The two remaining windings are randomly twisted at one point with 2 leads, and the remaining pair is connected to a voltmeter and power is supplied to the transformer. Its output voltage is transformed into other windings with the same value, since they have an equal number of turns.

Due to the alternate connection of the 2nd and third windings, the voltage vectors will add up, and the voltmeter will show their sum. How to check the parking sensors sensor with a multimeter (tester. In our case, if the direction of the windings coincides, this value will be 24 volts, and with different polarity - 0.

It remains to mark all the ends and perform a control freeze.

The article gives a general procedure for checking the technical condition of some random motor without certain technical features. They are subject to change on a case-by-case basis. See the documentation for your hardware for details.