How to check the winding of an angle grinder with a multimeter

Table of Contents

How to check the stator and rotor of an angle grinder

If the breakdown of the insulation was small and you found it, you need to clean the place of fouling and check the resistance. If its value is normal, insulate the wires with asbestos. On top drip a quick-drying glue like “Supermoment”. It will seep through the asbestos and insulate the wire well.

Angle Grinder Diagram. How does it work

If you still can not find the place of the insulation breakdown, try to soak the winding carefully with impregnation electrolysis varnish. Pierced and un-pierced insulation will be soaked in this varnish and become stronger. Dry it in a gas oven at about 150 degrees. If that doesn’t help, try rewinding or changing the armature.

Soldering the collector blades

The lamellae are mounted on the plastic backing. They may be worn down to the core. The only thing left is the edges where the brushes can’t reach.

Such a collector can be repaired by soldering.

  • From a copper tube or plate, cut as many lamellas as you need.
  • After you have stripped the armature of the rest of the copper, solder with ordinary tin and solder acid.
  • When all lamellae are soldered, grind and polish. If you don’t have a lathe, use a drill or screwdriver. Insert the armature shaft into the chuck. First sand it down with a file. Then polish with emery paper. Don’t forget to clean the slots between the lamellae and measure the resistance.
  • There are lamellae that are not completely damaged. In order to restore them, more careful preparation must be carried out. Lightly grind the collector to clean the plates.

Check and repair the angle grinder armature with your own hands 1

Almost all appliances used in the home use an asynchronous electric motor. An important advantage of this type of motor is that when you change the load on it, the speed does not change.

This means that if, for example, you cut a stone with a household angle grinder for a long time without stopping, you will not notice any external signs of motor overload. Speed of disc rotation will be constant and the sound will be monotonous.

Only the temperature will change, but you may not notice it if your hands are wearing gloves.

Collector of asynchronous motor is sensitive to overheating

If you are not careful, the advantage can turn into a disadvantage. Asynchronous motors are very sensitive to overheating, a significant excess of operating temperature leads to melting of the insulation on the rotor winding.

At first, the motor will work intermittently, and then. when there is an inter-turn short circuit. the motor will stop altogether. It is worth several times to overheat the motor of the angle grinder and, most likely, the armature will melt.

In addition, the high temperature causes the contacts that connect the primary winding wires to the collector to desolder, leading to an interruption in the electrical current flow.

How to determine if the angle grinder armature is faulty

Signs of breakage of the angle grinder armature are: increased sparking of brushes on the motor collector, vibration of the motor at low speeds, rotation of the working shaft in different directions. If these symptoms are present, you should stop working with the tool because it is dangerous. It’s easy to check suspicions with simple tests.

Visual inspection from outside

You should start troubleshooting with a visual inspection of the angle grinder:

  • Conduct a general inspection of the tool.
  • Check that the electric cable is intact and there is voltage in the socket.
  • Using a voltage indicator, check that the motor collector and start button are energized.

Use an indicator to check the electric continuity

Inspection of the appliance from the inside

If there is nothing wrong with the power supply but the angle grinder does not work, you have to open the housing to get access to the motor. Disassembly is usually straightforward. But it is necessary to adhere to simple rules that will avoid trouble during reassembly:

  • Be sure to unplug the unit before disassembly.
  • Remove the work disk and protective cover from the spindle.
  • Open the case in a well-lit place, on a clean table surface.
  • Note the location of all the parts and components before disassembling. It is a good idea to make a sketch or take a photo of the inside of the appliance.
  • Screws and fixing screws should be stored in a separate place so that they are not lost.

It is best to inspect the motor under a bright light so that all the fine details can be seen clearly. The armature must rotate freely about its axis, and proper functioning bearings should not make a sound.

There must be no sign of melted wiring on the armature and the windings must be intact, without rips. You can smell the rotor. If there is a short circuit between the windings, the insulation varnish will burn up and give off a persistent specific smell.

But this diagnosis requires a certain amount of experience.

Carry out a continuity check with a tester

If the visual inspection does not yield obvious results, it is advisable to continue the inspection with a multimeter.

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With the tumbler switch in the ohmmeter position (200 ohm range), you must use two feelers to “probe” the two adjacent blades of the armature. If the resistance on all windings is identical, then the windings are OK.

If the tester shows a different resistance or an open circuit on some pairs, there is a fault in this coil.

Check the continuity of the coils with a multimeter in resistance measurement mode

A wire break may occur between the winding and the core. You should carefully inspect the connection points of the coils with the collector blades at the bottom of the armature, visually check the solder contacts.

Check the contacts with the light bulb

If you don’t have a tester, you can get out of this situation with a simple 12 volt light bulb. The power can be any, optimally 30-40 watts.

12 volt battery power should be applied to the angle grinder’s plug, with a light bulb inserted in the gap of one wire. If the armature is functioning, if you rotate the spindle by hand, the light should be on without changing the brightness.

If the incandescence changes, it is a sure sign of an inter-turn short circuit.

If the bulb does not light, however, it may indicate the following:

  • The brushes may be stuck in an inoperative position. Retaining spring has failed.
  • There is an open circuit.
  • A short or rupture in the stator winding.

There are other ways to diagnose, but they require more sophisticated equipment that is not usually used at home. An experienced craftsman will locate the breakage with a high degree of accuracy using a “puncher” or a simple transformer with a cut toroidal core and one primary winding.

When the armature can be salvaged and repaired with your own hands

If the armature damage is identified with certainty, the part must be removed from the motor. Disassembly of the motor must be carried out with special care, by first removing the brushes and disconnecting the power supply terminals. Take out the rotor with the bearing blocks and the motor cooling impeller, they make one piece.

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If most of the wiring is damaged and the armature is out of balance as a result of overheating, it is better to replace the whole armature. Unbalanced condition is indicated by increased vibration and irregular hum during operation of the mechanism.

How to rewind an armature. step-by-step instructions

If the armature is not out of balance, and the problem is only in damaged windings, then such an armature can be restored by yourself by rewinding the coils. Rewinding the rotor at home requires a lot of patience and care.

Visual inspection

If the tool body is unevenly heated, you may detect a malfunction. Touching with your hand, you can feel the temperature differences in different areas of the housing. If this is the case, you should disassemble the tool and check it with a tester or other methods.

If you notice a short circuit in the stator windings and look for faults, first inspect the windings and the leads. Generally, when the windings are shorted, the current flow through them increases and overheating occurs.

There is more winding short circuit in the stator windings and the insulation layer is damaged. So we begin defining faults by conducting a visual inspection. If no burns or damaged insulation are found, then proceed to the next step.

Probably the cause of the breakdown in the failure of the voltage regulator, which occurs when the excitation currents increase. To find the problem check the brushes, they should be uniformly ground and have no chips or damage. Then check with a light bulb and 2 batteries.

Possible electrical faults

Faults in the electrical part of the Bosch angle grinder can be roughly divided into simple and complex.

Simple electrical faults on the Bosch angle grinder

If you turned on the angle grinder and it refuses to work, start troubleshooting with a broken power cord. Most often the wire breakage is evident at the entry point to the angle grinder or plug. Do not allow twisting, it will cause a short circuit in the tool.

To determine such a malfunction, open the handle covers of the angle grinder. Bosch angle grinders up to 1000 W have a single screw to fix the cover at the end. On Bosch angle grinders over 1000 W, the handle cover is secured with several screws.

Use a tester to test the power supply circuits from the input plug pos.5 to the switch. If the circuit is intact, proceed to check the switch operation. Bosch power tools have simple on/off switches that are controlled by the on/off lever.

But the electrical contacts in the switch will burn out and cause the angle grinder to malfunction. Repairing the contacts of a plastic switch is not a good idea, you have to replace it with a new one.

If the switch is intact, use a tester to check the circuit from each prong of the plug to each carbon brush.If circuits are intact the angle grinder should start. If it will not turn, then there is a mechanical problem. Jamming of gears or bearing damage is possible.

Checking the motor

If your Bosch angle grinder picks up speeds regardless of you, starts to get very hot, sparks, you need to pay attention to the integrity of the windings of the rotor, stator. Unintentional revolutions of the angle grinder are indicative of a defective stator winding. The integrity of the windings can be checked with a tester, and the short circuit between the coils can be checked with a special tool. Angle grinder’s involuntary rpm indicates a faulty stator winding. The integrity of the windings can be checked with a tester, and a short circuit between the coils can be checked with a special tool

Unintentional rotational acceleration of an angle grinder is an indication of a defective stator winding. The integrity of the windings is checked with a tester, and the short circuit between the coils is checked with a special device.

How to determine if the rotor is defective

Repair of the rotor is a complex technological process, accessible to craftsmen with straight hands.

Rotor malfunction is indicated by drop of engine rpm, appearance of long sparkling traces at one of brushes. This is the first sign of a shorted armature winding.

check, winding, angle, grinder, multimeter

It is preferable to have the rotor repaired by a specialized workshop. And you can rewind and on your own, if you decide to make your own repair of angle grinder Bosch with your own hands.

Dark color of rotor winding and burned collector lamellae indicate short circuit in rotor circuits. The problem can only be repaired by exchanging the stator for a new one.

Repair of stator

Repair of angle grinder Bosch includes the restoration of the stator. The main sign of stator failure is the spontaneous increase in speed of the running angle grinder, which can not be reduced by adjustments.A burned stator winding changes color and becomes darker. The core of the stator also darkens from high temperature.

The stator is easier to rewind, but even here you need to follow certain rules and follow a certain sequence.

If you have removed the cover of the stator housing, carefully inspect the condition of the carbon brushes and rotor manifold lamellae.

Carbon brushes must be at least 8 mm long. By the way, in Bosch angle grinders are used carbon brushes with a “shot”, a device that stops the angle grinder at the minimum length of the carbon brush.

Collector blades must not show any signs of carbon build-up or wear. Carbon deposits are easily removed with absorbent cotton soaked in alcohol.

Speed regulator malfunctions

The Bosch brushcutters, especially the smaller ones, are equipped with speed controllers. The speed regulator is accessed by opening the knob of the stator housing, held by one end screw.

The speed range of the speed regulator can be adjusted with a potentiometer hidden in the knob panel.

check, winding, angle, grinder, multimeter

Faulty regulator is easy enough to remove, because it is mounted only on the guide.

Repair of the speed regulator angle grinder is a complex process, which requires not only expertise, but tools and equipment.

If speed regulator is out of order and there is no new one, disconnect supply wires and install jumper.

Jumper installed in case of speed regulator failure is shown in red.

Causes of breakdowns

Anchor angle grinder. the rotor, is the part that is subjected to the highest loads: thermal, mechanical and electromagnetic. Violations of the rules of operation, prescribed by the manufacturer, leads to a rapid failure of this node. Some of the factors of such violations are:

  • Exceeding the permissible continuous running time;
  • Lack of protection against aggressive media. dust, sand, dirt, moisture;
  • exceeding the load parameters;
  • mechanical damage
  • operation at the moment of voltage fluctuations.

These causes can lead to the following armature malfunctions

  • melting of insulation (insulating varnish) of contacts or winding as a result of overheating;
  • mechanical damage: scratches, chips, cracks, from contact with foreign particles caught in the compartment with moving parts;
  • Breakdown in the weak points of the winding, caused by overloading;
  • distortion or imbalance of the anchor shaft;
  • Short circuit or the appearance of fouling on the lamellae.

To eliminate the cause of the breakdown, it is necessary to study the device of the anchor angle grinder and conduct appropriate diagnostics.

How to check the serviceability and perform repair of the angle grinder armature with your own hands, step by step instructions, video

As Shakespeare said, “Nothing lasts forever under the moon.”. Household appliances, alas, are no exception. It happens that even the most reliable mechanism fails. And you must be prepared to face this fact without panic, with the firm belief that there is no such thing as a hopeless situation.

How is the angle grinder arranged, what can be faults, how to check the motor armature, determine the cause of failure and troubleshooting? Knowledge of the device of the main units of the power tool will allow the master with his own hands to diagnose and repair the angle grinder.

Peculiarities of operation of asynchronous motor of angle grinder

Almost all electrical appliances used in the home, asynchronous electric motor is used. An important advantage of this type of motor is that when the load on it changes, the speed does not change.

This means that if, for example, you cut a stone with a household angle grinder for a long time without stopping, you will not notice any external signs of motor overload. The speed of the disc is constant and the sound is monotonous.

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Only the temperature will change, but you may not even notice it if your hands are wearing gloves.

Asynchronous motor manifold is sensitive to overheating

If you are not attentive, the advantage can turn into a disadvantage. Asynchronous motors are very sensitive to overheating, a significant excess of operating temperature leads to melting of the insulation on the rotor windings.

At first, the motor will falter and then, after a short circuit, the motor will stop altogether. It is worth several times to overheat the angle grinder motor and, most likely, the armature will melt.

In addition, the high temperature will de-solder the contacts that connect the primary winding wires to the collector, leading to an interruption of the electric current.

How to Determine Angle Grinder Armature Failure

Signs of angle grinder armature failure are: increased sparking of brushes on the motor collector, vibration of the motor at low speeds, rotation of the working shaft in different directions. If these symptoms are present, you must stop using the tool because it is dangerous. Suspicions are easy to check with simple tests.

Visual inspection from the outside

Troubleshooting should begin with a visual inspection of the angle grinder:

  • Carry out a general inspection of the tool.
  • Pay attention to the integrity of the power cord, the presence of voltage in the socket.
  • Using a voltage indicator, check that the motor collector and the start button are energized.

Use an indicator light to check the continuity of the electric circuit

Visually inspect the inside of the appliance

If all is well with the power supply, but the angle grinder does not work, you will have to open the housing to get access to the motor. Disassembly is usually straightforward. But it is necessary to adhere to simple rules that will avoid trouble during reassembly:

  • Always disconnect the appliance from the mains before disassembling.
  • Remove the blade and guard from the spindle.
  • Open the housing in a well-lit area, on a clean table surface.
  • Be sure to note the location of all the parts and assemblies before disassembling. It is recommended that you draw or photograph the interior of the appliance.
  • Keep screws and fastener screws in a separate location so they don’t get lost.
check, winding, angle, grinder, multimeter

Electric motor chek. How to test if field coil is damage.

It is best to examine the motor under a bright light, so that all the fine details can be clearly distinguished. The armature should rotate freely about its axis, and properly functioning bearings should not make a sound during operation.

There should be no sign of melted wires on the armature, and the winding circuits should be intact and without rips. You can smell the rotor. If there is a short circuit between the windings, the insulating varnish will burn and give off a strong, specific smell.

But this diagnosis requires a certain amount of experience.

Check circuits with a tester

If visual inspection is inconclusive, it is advisable to continue the test using a multimeter.

With the mode selector in the ohmmeter position (200 Ohm range) use two feelers to probe the two adjacent armature lamellae. If the resistance of all windings is the same, the windings are fine.

If on some pairs the tester shows a different resistance or breakage of a circuit. there is a fault in this coil.

Check the continuity of the coils with a multimeter in resistance measurement mode

A wire break may occur between the winding and the core. You should carefully inspect the connection points between the coils and the collector blades at the bottom of the armature, and visually check the solder contacts.

Check the contacts with a light bulb

If there is no tester, you can get out of the situation with a simple 12 volt bulb. The power can be any value, the optimal value is 30-40W.

Give 12 volt battery voltage to the angle grinder plug, insert a light bulb in the gap of one wire. If the armature is intact, if you rotate the spindle by hand, the bulb should light up without changing brightness.

If the glow changes, it is a sure sign of an inter-turn short circuit.

If the light bulb does not light up, it may indicate the following:

  • Brushes may be stuck in a defective position. The retaining spring is defective.
  • Circuit breakage.
  • There was a short circuit or a break in the stator winding.

There are other diagnostic methods, but they require more sophisticated equipment that is not usually used at home. An experienced technician will determine the breakage with a high degree of accuracy, using a “puncher” or a simple transformer with a cut toroidal core and one primary winding.

In what cases you can save the armature and repair it with your own hands

If the damage to the armature is established with certainty, the part must be removed from the motor. The motor must be disassembled with the utmost care, firstly the brushes must be removed and the power terminals disconnected. The rotor is removed along with the motor’s support bearings and cooling impeller, they form one piece with it.

How to check the angle grinder stator for inter-turn short circuits

It doesn’t take much time to check the stator and rotor for interturn faults with a multimeter. It will take longer to disassemble the motor. angle grinder, drill, rotary tool. each tool can be repaired by identifying the fault. It is better to break the check into several basic steps, and consistently take your time to perform the actions.

External Inspection

A malfunction can be detected by uneven heating of the tool body. When you touch the tool with your hand, you can feel the temperature differences in the housing. In this case the tool should be disassembled and checked with a tester or other methods.

If there is a short circuit in the stator coils and troubleshooting, first inspect the coils and leads. Generally, the current flowing through the windings increases when there is a short circuit and causes the windings to overheat.

There is more short-circuiting in the stator windings and the insulation layer is damaged. That is why we begin identifying faults by a visual inspection. If no burns or damage to the insulation are found, then proceed to the next step.

Probably the cause of the fault is a faulty voltage regulator, which occurs when the excitation currents increase. To find the problem check the brushes, they should be uniformly grinded and have no chips and damage. Then check with a light bulb and 2 rechargeable batteries.

Using a multimeter

Now check the stator winding breakage. On the scale of the multimeter, set the switch to the resistance measuring sector. Without knowing the measurement value, set the maximum value for your device. Check the tester for operability.

Touching each other with the probes. The arrow should read 0. Carry out the operation by touching the leads of the windings. If the reading on the scale of the multimeter is infinite, the winding is faulty and the stator has to be rewound.

Check for a short-circuit on the winding frame. Such a fault will cause a decrease in power of the angle grinder, the possibility of electrocution and an increase in temperature during operation. The operation is carried out according to the same scheme. Turn on the resistance measurement on the scale.

Place red probe on the winding lead and black probe on the stator case. If a winding is short-circuited to ground, the resistance value on the scale of the tester will be lower than that of an intact winding. This fault requires the stator windings to be rewound.

Now it’s time to measure and check if there is an inter-turn short circuit in the stator winding. To do this, measure the resistance value of each winding.

Determine the zero point of the windings by measuring the resistance for each winding. If the instrument shows the lowest resistance value of the winding, it must be replaced.

Non-standard test

The most accurate way is to check the stator with a metal ball and a step-down current transformer. The stator is connected to the leads of the three phases from the transformer. After checking the correctness of the connection, connect our circuit with undervoltage to the mains.

Throw a ball inside the stator and watch how it behaves. If it “stuck” to one of the windings, it means that there was an inter-turn short circuit. Ball rotates in a circle. stator is serviceable. Rather unscientific, but effective method for detecting a short circuit in the stator.

Rotor Faults

In the case of optimum use, the rotor will not wear out. Routine work is performed with the replacement of brushes if they are worn. But over time, with heavy loads, the stator heats up and builds up fouling. The most common mechanical failure is bearing wear or misalignment.

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The angle grinder will work, but the plates will quickly wear out and the motor will eventually break. To avoid breakage, you need to check the tool and maintain normal operating conditions.

Moisture on the metal causes the formation of rust. The friction force increases, more current is needed for work. Significant heating of contact groups, solder, strong spark.

How to Test an Electric Motor Armature

Household appliances and equipment have different types of electric motors. These differences depend on conditions of use, purpose, and function. For example, electric drills, mixers, food processors, vacuum cleaners, washing machines, and other appliances with frequently changing shaft speeds use collector motors.

If long-term stable operation is required, asynchronous motors are used in such equipment, which are most suitable for small makeshift machines.

Nevertheless, in all cases, you often have to solve the question of how to check the armature of the electric motor at home.

Modern services are quite expensive, so many people try to locate faults and make repairs themselves.

Collector motors and main armature faults

Collector motors are designed for 220V domestic power supply. Almost all of them are synchronous units. In contrast to asynchronous motors, commutator units consist of a stationary stator and a rotating winding on the shaft. the armature. They are energized by a brush-and-graphite device, which is the collector.

The primary reason for checking the armature and other parts is the occurrence of sparks. Active sparking indicates that the brushes and collector assembly are worn or that the contacts are broken.

over, sparks can also occur as a result of an inter-turn fault, i.e. a short circuit of the windings in the collector.

The occurrence of such abnormalities requires good diagnosis, starting with a visual inspection and ending with a multimeter test.

Initial inspection can identify broken or burned-out windings, as well as burnout at the points of their connection.

Therefore, the first thing to pay attention to is the condition of the windings and the integrity of the windings. If the windings are blackened in whole or in part, this is already an indication of some problem with the armature.

Sometimes you just need to sniff the insulation to detect a distinctive burning odor.

accurate information can be obtained by testing the armature with a multimeter. The wire tap is performed in stages, capturing all elements of the motor:

  • First test the winding connection points on the stator to the armature lamellae. The resistors on each of these must have the same value.
  • Next, the resistance between the lamellae and armature body is checked. In normal operation it should be infinite.
  • The continuity of the windings will be checked by testing the winding leads.
  • Then the condition of the circuit between the stator body and the armature winding leads is checked. If there is a breakdown on the case, it is strictly forbidden to connect the household device to voltage. In this case, obligatory repair or complete replacement of defective parts is required.

After repairing the collector motor you need to connect all the elements with each other and connect the device to 220V power. If the unit works properly, then the repair is correct.

Checking an asynchronous motor

In addition to the collector, in the home you can meet and asynchronous motors, installed in some models of washing machines or in refrigerator compressors.

Much more often they are used in compressors, pumps, various machines and other equipment. Despite the high reliability, these motors are also subject to breakdowns and malfunctions.

In these designs, the role of the armature is performed by the stator windings, so a visual inspection should begin with them.

Often the windings stop working when they get damp or, there was a breakage of windings. Therefore if the motor has not been used for a very long time, it is necessary to carry out an insulation resistance test with a megohmmeter. If no megohmmeter is available, it is recommended that the machine be disassembled and the stator windings dried for several days as a precaution.

It is possible that the cause of the malfunction is not the motor itself, but is related to other factors. Therefore, before you begin to repair the unit itself, you should make sure that there is voltage, check the magnetic starters, connection cables, thermal relay.

If there is a capacitor in the circuit, it too must be checked. If all of the above items are serviceable, you can proceed to disassemble the motor for an initial inspection. This check must be carried out with the power supply definitively disconnected.

Unintentional or erroneous switching on of the machine must be prevented.

During the inspection the stator windings are checked particularly carefully in addition to other parts. They must be intact and free of protruding or broken wires. Particular attention should be paid to black spots indicating possible burned-out wires. When in good condition, the conductors are dark red in color.

Blackening occurs when the electric insulating varnish applied on their surface is burned out. On examination it can be detected that the winding is partially or totally burned out and there is a short circuit between the windings. In case of partial burnout, the motor will run and heat up quickly.

Therefore the complete winding has to be rewound in any case.

If the external inspection is inconclusive, further diagnostics should be carried out with measuring instruments. Most often, for this purpose use a multimeter to determine the integrity of the winding, the presence or absence of a breakdown on the body.

In 220 V motors, the start winding and the work winding are tested. Resistance of the starting motor must be 1.5 higher than that of the working motor. In 380V electric motors, connected in star or delta connection, the circuit is disassembled and then each winding is tested in turn.

The resistance on each of them should be the same, with a deviation of no more than 5%. Also all the windings must be tested with each other and with the case. If the resistance value is not infinite, it indicates a breakdown of the windings on the ground or between them.

In this case it is necessary to rewind them completely.

Check the insulation resistance of the motor windings separately. In this case, the multimeter is not helpful, you need a megohmmeter for 1000 V connected to a separate power source.

Using a multimeter

Now check the possibility of stator winding breakage. On the scale of the multimeter set the switch to the sector of resistance measurement. Without knowing the measurement value, set the maximum value of the value for your device. Check if the tester works correctly.

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Touching each other with the probes. The needle of the device should show 0. We work by touching the leads of the windings. If the multimeter scale shows an infinite value, the winding is faulty and the stator should be rewound.

Checking the possibility of a short circuit to the housing. Such a malfunction will cause a reduction in power of the angle grinder, the possibility of electrocution, and an increase in temperature while working. The work is carried out according to the same scheme. Turn on the scale to measure the resistance.

place the red probe on the stator winding lead and the black probe on the stator body. If there is a short circuit of the winding to the housing, the resistance value on the scale of the tester will be lower than on the serviceable one. This fault requires the stator windings to be rewound.

Now is the time to measure and check whether there is a short circuit in the stator winding. To do this, the resistance value on each winding is measured. Determine the zero point of the windings by measuring the resistance for each winding. If the instrument shows the lowest resistance of the winding, it should be changed.

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