How to check the health of an electric motor with three outputs. How to check the windings of an electric motor with a tester, video, checking the stator for an interturn short circuit. How to ring an electric motor on a stand

Modifications of electric motors differ from each other, as well as their defects. Not every fault can be diagnosed using a tester, but in most cases it is quite possible.

Repairs begin with a visual inspection: are there any damaged parts, is the electric motor flooded with water, is there a smell of burnt insulation, and so on. The winding in an induction motor can burn out due to a short circuit between two adjacent turns. The unit overheats due to overloads and high currents.

Often, burnt windings are visible during visual inspection, in which case any measurements will be unnecessary. When there is no chance of correction, you need to remove and replace the windings with new ones. Sometimes it is necessary to check the electric motor more thoroughly.

First you need to study the configuration of the motor, for example, which windings are used. All rotating machines have two parts: a stator and a rotor.

In electric motors direct current available:

field winding, which is important for production magnetic field. It allows you to convert energy from mechanical to electrical and vice versa;
armature winding that carries the current load and regulates the alternating current to reduce eddy losses.

Engine alternating current, usually consists of two parts:

a stator having a coil for generating a rotating magnetic field;
a rotor attached to the output shaft and designed to produce a second rotating magnetic field.

How to check the integrity of the motor windings?

Using a multimeter and a few available tools, you can check:

single- and three-phase asynchronous motors;

DC and AC commutator motors;

asynchronous motors with squirrel-cage, phase-wound rotor.

Coil Winding Testing

There is a simple test used to check the condition of the motor coil. Why is the resistance of the windings measured, which varies depending on the length, thickness and material of the wire. If the resistance is too low, it indicates an insulation short circuit between turns.

You can use a multimeter, but it is better to check it with a megohmmeter because it uses more high voltage when checking resistance. This eliminates false readings caused by the inductance of the motor coil.

The test shows the quality of the wire insulation, which is determined by the resistance of the measured part of the system. The results obtained are compared with tabular data of permissible cable insulation resistances up to 1 kV, set out in the rules for electrical installations (PUE). The test results can predict a failure before it actually happens. This allows the production shop to repair or replace equipment during operation.

How to check an electric motor coil with a multimeter can be seen in the video:

Anchor diagnostics

You can also check the serviceability of the electric motor using a special digital armature testing device E236. To do this, place the anchor on the prism of the device, which is then connected to the network.

The diagnostic process includes the following steps:

position the hacksaw blade parallel to the groove of the part being examined;
holding the metal with one hand, slowly turn the anchor with the other.

If there is an interturn closure, the blade located close to the groove will begin to vibrate and be attracted to the mechanism.

A visual demonstration of checking the anchor is shown in the video:

How to ring an electric motor on a stand

To quickly detect a break in the engine circuits, you can use a work stand with a DC source, an inverter, a digital voltmeter, a voltage comparator, an indicator light and a break buzzer.

It is also possible to determine the interturn short circuit.

Conclusion

It is not always possible to purchase expensive special-purpose devices. Therefore, it is important to know how to check the engine with a simple multimeter, a very useful electrical measuring device in the household. It replaces many separate tools needed to test circuits.

You can watch a video lesson on checking the stator for a break here:

When a household electrical appliance breaks down, you have to check all its components separately.

And if testing the sensors does not cause any difficulties - it is usually enough to check the resistance, then with the engine everything is not so simple.

This unit is much more complex, and in order to identify its malfunction, you need to know the testing procedure. Next, we’ll talk about how to test an electric motor with a multimeter.

If there is no mechanical damage in the engine, which is usually determined visually, then its malfunction in most cases is due to the following:

there is a break in the internal circuit;
a short circuit has occurred, that is, contact has appeared where there should not be one.

Both defects are detected. Difficulties arise only when checking: in most of them the winding has almost zero resistance and it has to be measured by an indirect method, for which you will need to assemble a simple circuit.

The most popular AC motors are:

Three-phase asynchronous motors also operate with single-phase power.
Asynchronous single- and two-phase capacitors with squirrel-cage rotor. Most household appliance motors belong to this type.
Asynchronous with wound rotor. Such a rotor has a three-phase winding. Motors with a wound rotor are used where it is necessary to regulate the rotation speed and reduce the starting current: in crane equipment, machine tools, etc.
Collector. Used in hand-held power tools.
Asynchronous three-phase with squirrel-cage rotor.

The popularity of motors of the latter type is explained by a number of advantages:

simplicity of design;
strength;
reliability;
low cost;
unpretentiousness (does not require maintenance).

All electric motors consist of two parts: stationary and rotating. The first in AC motors is called the stator, y is called the inductor; the second - respectively, the rotor and armature.

Repair of asynchronous motors

Of the asynchronous motors, the most common are two- and three-phase. They are tested differently. Let's look at each variety in detail.

Three phase motor

The stator winding of such a motor consists of three parts (phases), separated by 120 degrees and connected in a star or delta configuration. The engine operates when the following conditions are met:

winding is done in the correct order;
there is reliable insulation between the turns, as well as between live parts and the housing;
All connections have good electrical contact.

First, the insulation resistance between live parts and the housing is checked. It is more correct to do this with a megger - a tester capable of generating voltages up to 2500 V and measuring resistances up to 300 GOhm. A more common multimeter will also work: it will not allow you to accurately measure resistance, but it can detect breakdown. The measuring range switch is set to maximum value- 2 or 20 MOhm.

Three-phase asynchronous motors

Measurements are performed in this order:

check the functionality of the device by applying the probes one to the other: normally, the display shows a meager value or a number with two zeros in front;
touch both probes to the motor housing: if there is contact, the multimeter will also show scanty resistance;
Continuing to hold one probe on the body, the second touches the terminals of each phase in turn: normally, the megohmmeter shows 500 - 1000 MOhm or more, the multimeter shows one (symbolizes infinity).

Winding integrity: this operation is convenient to perform by switching the multimeter to the continuity mode. If there is no break in the circuit, the device will sound a sound signal, that is, the user does not have to read the readings on the display. The ends of each winding are located in a terminal box. The absence of a sound signal or a high resistance value on the display indicates an open circuit.
Short-circuited turns: their resistance (a multimeter is enough) must be within certain limits. An overestimated value indicates a break, a low value indicates an interturn short circuit.

Finally, the resistance of the windings is measured. A difference of no more than 1 ohm is allowed.

With a larger mismatch, the winding with less inductance burns out due to the higher current.

Two-phase electric motor

The stator has two windings:

working;
launcher

They measure the resistance of each with a multimeter and compare: normally, the starting resistance is twice as high as that of the working one.

The motor is also checked for short circuits between live parts and the housing - according to the same scheme as a three-phase one.

Checking commutator electric motors

Commutator motors have sections or lamellas where the brushes fit.

Check procedure:

Use a multimeter to determine the resistance between adjacent lamellas. Normally, the values for each pair are the same. In the event of a break (infinitely high resistance) or short circuit (minuscule resistance), the engine tachometer is replaced.
The resistance between the commutator and the rotor housing is measured: normally it is infinitely high.
The stator windings are checked for integrity.
Check the resistance between the stator housing and live parts: normally - infinitely high.

A high-precision low-value resistor (about 20 Ohms) is connected in series with the coil. Resistors with a tolerance of no more than 0.05% are called high-precision. They have a gray stripe in their color marking (not to be confused with silver).
The coil-resistor circuit is connected to a DC source of 12 V or higher. The higher the voltage, the more accurate the measurements. A car battery or computer power supply is used as a 12 V source.
Use a multimeter to measure the voltage drop across the coil. It is important to observe polarity here: the probe connected to the COM port (negative potential) is shorted on the negative or ground side; the second (connects to the “V/Ω” connector) - from the “plus” side.

The multimeter measures voltage much more accurately than resistance - with an accuracy of up to 0.1 mV. This is what the indirect method is based on.

Then the coil resistance is calculated using the formula: Rcat = Ucat * Rres / (12 – Ucat), where

Rcat - coil resistance, Ohm;
Ucat - voltage drop across the coil, V;
Rres - resistor resistance, Ohm;
12 - power supply voltage, V.

Checking DC motors

Testing order:

Checking the winding resistance: such motors have low resistance, so it is also determined indirectly - by voltage and. You will need two multimeters: one used as a voltmeter, the other at the same time as an ammeter. The winding is supplied with power from a battery with a voltage of 4 - 6 V. The resistance is calculated using the formula: R = U / I.
Measuring the resistance of the armature windings and between the collector plates. Normally, the multimeter displays equal values.

For the resistance between the collector plates, the maximum permissible difference is 10%, in the presence of an equalizing winding - 30%.

Features of testing electric motors with additional elements

Electric motors are equipped with additional elements to optimize operation or protection.

Most often used:

Thermal fuses: disconnect the engine from the power supply when it reaches a temperature dangerous for insulating materials. They are located on the housing (attached with a bracket) or under the winding insulation. In the second case, the test is easier to perform because the conclusions are easily accessible. You can determine which detachable legs are connected to the protective circuit using a multimeter or a phase indicator (similar to a screwdriver with a light bulb). Normally, the resistance between the terminals of the thermal fuse is very small (short circuit).
Thermal relay: often used instead of thermal fuses. Usually they are normally closed, but there are also open ones. To diagnose, using the markings on the relay body, in reference books or on the Internet, find the resistance of its components, then check their actual value with a multimeter. To search on the Internet, type the relay brand in the line followed by “Data Sheet”. If the thermal relay burns out, an analogue is selected based on its parameters.
Three-terminal engine speed sensors. Installed in washing machines. The main element of the sensor is a metal plate on which, when small currents are passed through it, a potential difference is formed.

The sensor is powered through the two outer terminals. If you touch them with the probes of a multimeter in ohmmeter mode, it will normally display a negligible resistance.

Checking the third pin is only possible in operating mode when a magnetic field is present. Trying to ring the sensor on the go, that is, with the washing machine turned on, can lead to injury. It is safer to simulate the operating mode by removing the engine and powering the sensor separately. Pulses at the sensor output are formed by rotating the rotor.

A multimeter allows you to identify, if not all, but many breakdowns of an electric motor. Mainly, using continuity testing, breaks and short circuits are detected. Full diagnostics are carried out on special stands; a megohmmeter is required to measure the insulation resistance.

Adjustment of constant current motors

The adjustment of constant current motors is carried out in the following scope: external inspection, measurement of winding resistance to constant current, measurement of winding insulation resistance relative to the housing and among themselves, testing of turn-to-turn insulation of the armature winding, test run.

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

name or trademark of the manufacturer,

car type,

serial number of the car,

rated data (power, voltage, current, speed),

method of exciting the machine,

year of issue,

weight and GOST of the machine.

Motor winding terminals direct current must be firmly insulated from each other and from the housing, the distance between them and the housing must be more than 12-15 mm. Increased attention during an external inspection, pay attention to the commutator and brush mechanism (brushes, traverse and brush holders), because their condition significantly affects the switching of the machine, and, consequently, the stability of its operation.

When inspecting the commutator, make sure that there are no cutter marks, potholes, varnish and paint stains on the working surface, as well as traces of soot from unsatisfactory operation of the brush mechanism. The insulation between the collector plates should be selected to a depth of 1-2 mm, and a chamfer 0.5-1 mm wide should be removed from the edges of the plates (depending on the power of the motor). The spaces between the plates must be completely clean - there should be no iron shavings or filings, dust from graphite brushes, oil, varnish, etc.

The operation of a constant current motor, and especially its brush mechanism, is influenced by the commutator beating and its vibration. The higher the peripheral speed of the collector, the lower the permissible runout. For high-speed engines, the maximum permissible runout value should not exceed 0.02-0.025 mm. The magnitude of the vibration amplitude is determined by a dial indicator.

When taking measurements, the tip of the indicator is pressed against the surface in the direction in which the vibration needs to be measured. Because the surface of the commutator is discontinuous (the commutator plates and depressions 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 mm. But this device allows you to detect vibrations at speeds less than 750 rpm. For engines whose rotation speed exceeds 750 rpm, you need to use special devices - vibrometers or vibrographs, which allow you to determine or record the vibration of certain machine components.

Runout is also determined using an indicator. The manifold runout is determined both in the cold and in the heated state of the machine. When measuring, pay attention to the behavior of the indicator needle. Smooth movement of the arrow indicates sufficient cylindricity of the surface, and 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 beating is of a relative nature, because operational experience shows that there are engines in which the beating values are significant at low speeds, but at rated speed they work satisfactorily. Therefore, a 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 constant current motor, you should pay attention to the condition of the soldering and connections of the windings, bearing units, and the uniformity of the gap (with the engine disassembled). Gap measured in diametrically return 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 cages should move freely, but should not wobble. The usual gap between the brush and the cage 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 distribution of current, the pressure of individual brushes should not differ from the average by more than 10%. The specific pressure value is determined as follows. A sheet of thin paper is placed between the commutator and the brush, a dynamometer is attached to the brush, and then, by pulling the brush with a dynamometer, a position is found where the sheet of paper can be freely pulled out. The dynamometer reading at this moment corresponds to the brush pressure on the commutator. The specific pressure is determined by dividing the dynamometer reading by the area of the brush base.

Correct installation of brushes is one of the most important factors in the normal operation of the machine. Brush holders are installed in such a way that the brushes stand strictly parallel to the commutator 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 commutator as possible (the so-called staggered arrangement). This will allow the entire length of the commutator to participate in commutation, which contributes to more uniform wear. However, with such placement of the brushes, it is necessary to ensure that the brushes do not protrude during operation (taking into account the shaft run-up) beyond the edge of the commutator. Before starting the engine, the brushes are carefully rubbed onto the commutator (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, during operation, cause scratches on the commutator, thereby worsening the switching conditions of the machine.

How check collector electric motor multimeter - stator and rotor windings

Electric motor direct current. Principle of operation.

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

Before you begin checking whether the windings are turned on correctly, study the markings of the terminals of a particular type of machine. In DC motors, the winding terminals are marked first according to GOST 183-66 in capital letters their names with the addition after them of 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 motor, their beginnings and ends are marked with numbers 3-4, 5-6, etc. The designations of the terminals may correspond to the excitation circuits and directions of rotation of the motor, which are shown in Fig. 2.

The correct connection of the pole windings is checked to clarify the alternation of their polarity. The alternation of polarity of 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 a 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 alternating polarity of the poles can be determined in several ways: external inspection, using a magnetic needle, and using a special coil.

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

Rice. 1. Grinding of brushes to the commutator: a - incorrect; b - correct

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

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

The second method is used mainly for parallel excitation winding coils. The essence of this method is as follows. Current is supplied 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.

Mechanical part

The mechanical part of the electric motor, roughly speaking, consists of only two elements:

1. Rotor - a movable, rotating element that drives the motor shaft.
2. Stator - a housing with windings in the center of which there is a rotor.

These two elements do not touch each other and are separated only by bearings.

Checking the electric motor begins with an external inspection

First of all, the engine is inspected for any noticeable defects, these could be, for example, broken mounting holes and stands, darkening of the paint inside the electric motor, which clearly indicates overheating, the presence of dirt or foreign substances trapped inside the engine, any chips and cracks.

Bearing check

Most electric motor failures are caused by faulty motor bearings. The rotor should move freely inside the stator, the bearings, which are located on both sides of the shaft, should minimize friction.
There are several types of bearings used in electric motors. The two most popular types are brass plain bearings and ball bearings. Many of them have fittings for lubrication, while others have lubrication installed during production and are, as it were, “maintenance-free.”

To check the bearings, first of all, you need to remove the voltage from the electric motor and try to manually rotate the motor rotor (shaft).
To do this, place the electric motor on a hard surface and place one hand on top part engine, turn the shaft with your other hand. Observe carefully, try to feel and hear friction, scratching sounds, and uneven rotation of the rotor. The rotor should rotate calmly, freely and evenly.
After this, check the longitudinal play of the rotor; try to pull and push the rotor in the stator. A characteristic small backlash is acceptable, but no more than 3 mm; the smaller the backlash, the better. If there is a lot of play and bearing faults, the engine is noisy and quickly overheats.

It is often difficult to check rotor rotation due to the connected drive. For example, the rotor of a working vacuum cleaner motor is quite easy to spin with one finger. And in order to turn the rotor of a working rotary hammer, you will have to make an effort. Rotate the shaft of the motor connected through worm gear, it won’t work at all because design features this mechanism.
Therefore, it is necessary to check the bearings and the ease of rotation of the rotor only when the drive is turned off.

The reason for the impeded movement of the rotor may be a lack of lubrication in the bearing, thickening of the grease, or dirt getting into the cavity of the balls, inside the bearing itself.

Unhealthy noise during operation of the electric motor is created by faulty, broken bearings with increased play. In order to verify this, it is enough to shake the rotor relative to the stationary part, creating variable loads in the vertical plane, and try to insert and pull it out along the axis.

Electrical part of the electric motor

Depending on whether the motor is for direct or alternating current, asynchronous or synchronous, its design of the electrical part is also different, but general principles work based on the impact of rotating electromagnetic field stator on the rotor field which transmits rotation (shaft) to the drive.

In DC motors, the stator magnetic field is not created permanent magnets, but by two electromagnets assembled on special cores - magnetic cores, around which coils with windings are located, and the magnetic field of the rotor is created by the current passing through the brushes of the commutator assembly along the winding laid in the armature slots.
In asynchronous AC motors, the rotor is made in the form of a short-circuited winding into which no current is supplied.

In commutator electric motors, a circuit is used to transfer current from a stationary part to rotating parts using a brush holder.

Since the magnetic circuit is made of special steel plates assembled with high reliability, breakdowns of such elements occur very rarely and under the influence of aggressive operating conditions or extreme mechanical loads on the housing. Therefore, there is no need to check their magnetic fluxes and the main attention is paid to the condition of the electrical windings.

Checking the brush assembly

The graphite brush plates must create a minimum contact resistance for normal engine operation, they must be clean and fit well to the commutator.

An electric motor that has worked a lot with serious loads, as a rule, has dirty plates on the commutator with graphite shavings fairly packed into the grooves of the plates, which quite significantly worsens the insulation between the plates.

The brushes are pressed against the plates of the collector drum by spring force. During operation, the graphite is abraded and its rod wears out along the length and the clamping force of the springs decreases, and this in turn leads to a weakening of the contact pressure and an increase in the transient electrical resistance, which causes sparking in the commutator. Increased wear of the brushes and copper plates of the commutator begins.

The brush mechanism is inspected for contamination, for wear of the brushes itself, for the pressing force of the mechanism springs, and also for sparking during operation.

Dirt is removed with a soft cloth moistened with alcohol. The gaps (cavities) between the plates are cleaned with a toothpick. The brushes are rubbed in with fine-grained sandpaper.
If there are potholes or burnt areas on the collector, then it is subjected to machining and polishing to the desired level.

Checking windings for open or short circuit

Most simple single-phase or three-phase household electric motors can be checked with a conventional tester in ohmmeter mode (in the lowest range). It's good if there is a winding diagram.
The resistance is usually small. Great importance resistance indicates serious problem with electric motor windings that may have a break.

Checking for short circuit to frame

The test is carried out using a multimeter in resistance mode. Having hooked one tester probe onto the body, alternately touch the leads of the electric motor windings with the second probe. In a working electric motor, the resistance should be infinite.

Checking the insulation of the windings relative to the housing

To find violations of the dielectric properties of insulation relative to the stator and rotor, use special device— megohmmeter. Most household multimeters do an excellent job of measuring resistance up to 200 MΩ and are well suited for this purpose, but the disadvantage of multimeters is the low resistance measurement voltage, it is usually no more than 10 volts, and the operating voltage of the windings is much higher.
But still, if we couldn’t find a “professional device”, we’ll do the measurement using a tester. We set the device to maximum resistance (200 MOhm), fix one probe on the motor housing or on the grounding screw, ensuring reliable contact with the metal, and with the second one, without touching with hands, press the probe to the contacts of the windings. It is necessary to ensure reliable isolation of the probes from the hands and body, since the measurements will be incorrect.
The higher the resistance the better, sometimes it can be as low as 100 MOhm and this can be acceptable.

Sometimes in commutator motors, graphite dust can “pack” between the brush holder and the motor housing and you will see much lower resistance values; here you should pay attention not only to the windings but also to potential “breakdown” points.

Checking the starting capacitor

Check the capacitor with a tester or a simple ohmmeter.
Touch the leads of the capacitor with the probes; the resistance should start low and gradually increase as the small voltage supplied from the ohmmeter batteries gradually charges the capacitor. If the capacitor remains shorted or the resistance does not increase, then there is likely a problem with the capacitor and will need to be replaced.

Recently, friends and neighbors have often asked me the question: how to check an electric motor with a multimeter? So I decided to write short review instructions for novice electricians.

Let me note right away that one multimeter does not allow you to identify everything with a 100% guarantee. possible malfunctions: few of its functions. But they can easily find about 90% of defects.

I tried to make the instructions universal for all types of AC motors. These same techniques, with a thoughtful approach, can be used in DC voltage circuits.

What you should know about the engine before checking it: 2 important points

Within the framework of the presented topic, it is enough to present the simplified operating principle and design features of any engine.

Operating principle: what electrical processes need to be well understood during repairs

Any engine consists of a permanently fixed housing - a stator and a rotor rotating in it, which is also called an armature.

Its circular motion is created due to the influence of the rotating magnetic field of the stator on it, formed by the flow of electric currents through the stator windings.

When the windings are in good condition, rated currents flow through them, creating magnetic fluxes of optimal magnitude.

If the resistance of the wires or their insulation is broken, then leakage currents, short circuits and other damage are created that affect the operation of the electric motor.

The minimum possible gap is made between the stator and rotor. It can be violated:

broken bearings;
mechanical particles trapped inside;
incorrect assembly and other reasons.

When rotating parts touch a stationary body, their destruction and additional mechanical loads are created. All this requires a thorough inspection, analysis of the condition of the internal parts before electrical checks begin.

Quite often, unqualified analysis is an additional cause of breakdowns. Use it special tool and pullers to prevent damage to the shaft faces.

After disassembly, immediately during inspection they check for play, free movement of bearings, their cleanliness and lubrication, and correct seating.

In addition, the commutator motor may have severely worn plates or brushes.

All this must be checked before operating voltage is applied.

Design features affecting defect detection technology

Typically, the manufacturer indicates the electrical characteristics on a plate attached to the housing. This information is worth believing.

However, often during repair or rewinding the stator design changes, but the nameplate remains the same. This option should also be taken into account.

For a 220 volt household network the following motors can be used:

commutator with brush mechanism;
asynchronous single-phase;
synchronous and asynchronous three-phase.

Three-phase synchronous and asynchronous electric motors operate in 380-volt circuits.

They all differ in design, but, due to the work on general laws electrical engineering, allow the use of the same testing methods, consisting of measurements electrical characteristics indirect and direct methods.

How to check the motor winding on the stator: general recommendations

The three-phase stator has three built-in windings. There are six wires coming out of it. IN individual designs You can find 3 or 4 pins when the delta or star connection is assembled inside the housing. But this is rarely done.

Testing them with a multimeter in ohmmeter mode allows you to determine whether the ends are connected to the windings. You just need to place one probe on an arbitrary pin, and use the other one to alternately measure the active resistance on all the others.

The pair of wires on which resistance in Ohms is detected will belong to the same winding. They should be visually separated and marked, for example, with the number 1. Do the same with other wires.

Here you need to clearly understand that, according to Ohm’s law, the current in the winding is created under the action of , which is counteracted by the action we measure.

We take into account that the windings are wound from the same wire with the same number of turns, creating equal inductive reactance. If the wire is short-circuited or torn during operation, its active component, as well as its full value, will be disrupted.

The interturn short circuit also affects the value of the active component.

Therefore, measurements of the active resistance of the windings and their comparison make it possible to reliably judge the serviceability of the stator circuits and conclude that their integrity is not compromised.

Single phase asynchronous motor: features of stator windings

Such models are created with two windings: working and starting, such as, for example, washing machine. In the vast majority of cases, the active resistance of the working chain is always less.

Therefore, when only three ends are removed from the stator, this means that the resistance must be measured between all of them. The results of three measurements will show:

the smaller value is the working winding;
middle - starting;
large - serial connection of the first two.

How to find the beginning and end of each winding

The method only allows us to identify general direction windings of each wire. But for practical work the electric motor is more than enough.

The stator is considered as an ordinary transformer, which in principle is what it actually is: the same processes occur in it.

To operate, you will need a small constant voltage source (a regular battery) and a sensitive voltmeter. Better than a pointer. It displays information more clearly. It is difficult to monitor the change in sign of a rapidly changing pulse on a digital multimeter.

A voltmeter is connected to one winding, and voltage from the battery is briefly applied to the other winding and immediately removed. The deviation of the arrow is assessed.

If, when applying a “plus” to the first winding, an electromagnetic pulse was transformed into the second, deflecting the arrow to the right, and when it is turned off, it moves to the left, then it is concluded that the wires have the same direction when the “+” of the device and the source coincide.

Otherwise, you need to switch the voltmeter or battery - that is, change the ends of one of the windings. The next third chain is checked in the same way.

Personal experience: checking the stator windings of an asynchronous electric motor

For the article, I used my new one. At the same time, I continue to identify the shortcomings of its design, which I already showed in the article earlier.

Electrical tests were carried out on a three-phase motor connected to single-phase network through capacitors in a star circuit.

General assessment of the winding insulation condition

Since all the windings are already assembled together at the terminal terminals, I started taking measurements by checking their insulation resistance relative to the housing. One probe is located on the terminal block of the zero assembly, and the second is on the socket of the cover fastening screw. My Mestek showed no leaks.

I didn't expect any other result. This method of measuring the insulation condition is very inaccurate and it simply cannot detect most damage: 3 volt battery power is clearly not enough.

But it’s still better to do at least this way than to completely neglect such a check.

To fully analyze the dielectric layer of conductors, it is necessary to use the high voltage that megohmmeters produce. Its value usually starts from 500 volts and above. The home master does not have such devices.

You can do it indirectly, using a household network. To do this, a voltage of 220 volts is supplied to the winding and housing terminals through an incandescent test lamp with a power of about 75 watts (a current-limiting resistance that excludes the supply of phase potential to the circuit) and a series-connected ammeter.

The expected leakage current through normal insulation will not exceed microamps or their fractions, but you need to count on emergency mode and start measuring within amperes. By measuring the current and voltage, the insulation resistance is calculated.

However, such work produced under current voltage. She's dangerous. It can only be performed by those workers who have good practical skills as an electrician and have at least a third safety group.

When using this method, keep in mind that:

a full-fledged phase is supplied to the motor body: it must be located on a dielectric base and have no contact with other objects;
even a temporarily assembled circuit requires reliable insulation of all ends and wires, strong fastening of all clamps;
The lamp bulb may break: it must be kept in a protective case.

Measurement of winding resistance

Here you need to disassemble the wiring diagram and remove all jumpers. I switch the multimeter to ohmmeter mode and determine the active resistance of each winding.

The device showed 80, 92 and 88 Ohms. In principle, there is no big difference, and I explain deviations of several ohms by the fact that the crocodile does not provide high-quality electrical contact. Different transition resistance is created.

This is one of the disadvantages of this multimeter. The probe does not fit well into the crocodile groove, and besides thin metal the clamp moves apart. I immediately had to tighten it with pliers.

Measuring insulation resistance between windings

I show this principle because it must be followed between each winding. However, instead of an ohmmeter, you need a megohmmeter or, as a last resort, check with household voltage according to the method I described above.

A multimeter can be misleading: it will show good insulation where hidden defects will be created.

How to check an electric motor armature: 4 types of different designs

The rotor windings create a magnetic field, which is influenced by the stator field. They must also be in good working order. Otherwise, the energy of the rotating magnetic field will be wasted.

The armature windings have different designs for motors with wound rotor, asynchronous and commutator. This is worth considering.

Synchronous wound rotor models

At the anchor, wire leads are created in the form of metal rings located on one side of the shaft near the rolling bearing.

The wires of the circuit are already assembled before these rings, which causes small features to check them with a multimeter. You should not turn them off, however, the technique described above for the stator is, in principle, suitable for this design.

Such a rotor can also be conditionally represented as a working transformer. All you need to do is compare the individual resistances of their circuits and the quality of insulation between them, as well as the housing.

Asynchronous motor armature

In most cases, the situation here is much simpler, although there may be problems. The fact is that such a rotor is made in the shape of a “squirrel wheel” and is difficult to damage: a fairly reliable design.

The short-circuited windings are made of thick aluminum rods (rarely copper) and are firmly pressed into the same bushings. All this is designed for the flow of short circuit currents.

However, in practice, various damages occur even in reliable devices, and somehow they need to be found and eliminated.

A digital multimeter is not required to identify faults in the squirrel wheel winding. Here you need other equipment that supplies voltage to the short circuit of this armature and controls the magnetic field around it.

However, internal failures of such structures are usually accompanied by cracks on the body, and they can be noticed during a careful internal inspection.

Who is interested in such testing using electrical methods, watch the video of the owner Viktor Yungblyudt. He shows in detail how to determine the breakage of the rods of such a rotor, which makes it possible to subsequently restore the functionality of the entire structure.

Commutator motors: 3 winding analysis methods

Fundamental electrical diagram commutator motor in a simplified form can be represented by rotor and stator windings connected through a brush mechanism.

The diagram of an assembled electric motor with a commutator mechanism and brushes is shown in the following picture.

The rotor winding consists of parts connected in series with each other by a certain number of turns on the collector plates. They are all of the same design and therefore have equal active resistance.

This allows you to check their serviceability with a multimeter in ohmmeter mode using three different methods.

The simplest measurement method

I show principle No. 1 of determining the resistance between the collector plates in the photo below.

Here I made one simplification that cannot be made in a real test: I was too lazy to remove the brushes from the brush holder, and they create additional chains that can distort the information. Always take them out for accurate measurements.

The probes are placed on adjacent lamellas. This type of measurement requires precision and perseverance. You must mark the collector with paint or a felt-tip pen. From there you will have to move in a circle, taking sequential measurements between all successive plates.

Constantly monitor the device readings. They should all be the same. However, the resistance of such sections is small and if the ohmmeter does not respond to it accurately enough, then it can be sensed by increasing the length of the chain being measured.

Method No. 2: diametric measurement

This second method will require even greater care and concentration. The ohmmeter probes must be placed not on the nearest adjacent plates, but on diametrically opposite ones.

In other words, the multimeter probes should fall on those plates that are connected by brushes when the electric motor is running. And to do this, they will need to be marked somehow so as not to get confused.

However, even in this case there may be difficulties associated with measurement accuracy. Then you will have to use the third method.

Method No. 3: indirect method of comparing small resistance values

To measure, we need to assemble a circuit that includes:

12 volt battery;
powerful resistance of about 20 Ohms;
multimeter with ends and connecting wires.

It should be imagined that the measurement accuracy increases the stability of the created current source due to:

high battery capacity, providing the same voltage level during operation;
increased power of the resistor, eliminating its heating and deviation of parameters at currents up to one ampere;
short and thick connecting wires.

One connecting wire is connected directly to the battery terminal and the collector lamella, and a current-limiting resistor is inserted into the second, eliminating large currents. A voltmeter is placed parallel to the contact plates.

The next pairs of lamellas on the collector are sequentially moved with probes and readings are taken with a voltmeter.

Since the battery and resistor are on a short time For each measurement we produce the same voltage, the voltmeter readings will depend only on the resistance value of the chain connected to its terminals.

Therefore, with equal readings, we can conclude that there are no defects in the electrical circuit.

If desired, you can measure the current through the lamellas with a milliammeter and calculate the value of active resistance.

Checking the condition of the rotor windings of a commutator motor strongly depends on the accuracy class of the multimeter in ohmmeter mode.

My digital Mestek MT102, despite the shortcomings identified in it, copes well with this task.

DC motors

The design of their rotor resembles the armature device of a commutator motor, and stator windings are created to work with a switching circuit with parallel, series or mixed excitation.

The stator and armature testing methods disclosed above allow you to check a DC motor, both asynchronous and commutator.

The final stage: features of engine checks under load

You cannot make a conclusion about the serviceability of the electric motor by relying only on the readings of the multimeter. It is necessary to check the performance characteristics of the drive under load, when it needs to perform rated work using the applied power.

Turning the voltage on at idle and checking that the rotor begins to rotate, as some novice electricians do, is a typical mistake.

For example, the owner of a very short video of PrJSC Dunaisudoremont believes that by measuring the current in the windings, he was convinced that the repaired engine was ready for further operation.

However, such a conclusion can only be given after long work and assessments of not only current values, but also measurements of stator and rotor temperatures, analysis of heat removal systems.

Unidentified defects of improper assembly or damage individual elements may repeatedly require additional repairs with greater labor costs. If you still have questions on the topic of how to check an electric motor with a multimeter, then ask them in the comments. We'll definitely discuss it.