How to Check Stator Angle Grinder with a Multimeter

Angle grinders are solid and reliable devices in general. They can perform a fairly wide range of jobs. However, their periodic breakdowns are inevitable, any home master must know how they are eliminated.


Before talking about the main malfunctions in the work of the angle grinder, about the methods of dealing with them, it is necessary to understand the design features. Its study is greatly facilitated by the fact that the circuit of electrical and mechanical components in almost all angle grinders is approximately the same. Small differences are associated only with patented innovative solutions promoted by individual manufacturers, and with specific devices for individual functions. Almost any modern angle grinder is equipped with a shockproof plastic case. Usually it is made not monolithic, but broken into 2 components, which are connected with screws. Where the drive is located, vents are provided. The electric motor itself is formed by a combination of the following elements:

When creating a stator, bipolar coils are used, on which copper wire is wound. The total number of turns is selected very carefully. Defining it, engineers take into account the desired parameters of the device. The rotor is connected to the stator by bearings. The rotor itself is made of electrical steel. Slots are formed in it, allowing to place the wires of the winding. The number of grooves and winding features cannot be considered a trifle: it depends on these parameters at what speed the angle grinder can work. The role of brushes is the transfer of current between the cable and the collector.

On this review of the electrical components of the angle grinder can be completed, but it also has mechanical devices. Of great importance is the gearbox, the housing of which is made of a durable alloy based on aluminum. This material was chosen in connection with the combination of excellent strength and high thermal conductivity. The gear housing must allow reliable fixing of the apparatus elements. It provides holes in which the auxiliary handle is mounted. Using a gearbox, the force generated by the engine is transmitted. If this node breaks, then the angle grinder operation either becomes completely impossible, or occurs at the “wrong” speed.

The gear axis is equipped with a pair of bearings. From them the impulse receives a planetary driven gear. At the end of the shaft, a thread is provided for the nut clamping the trim discs. And the sun gear is pressed onto the axis of the anchor. She is the leading link for the bevel gear.

It is also necessary to say about the release coupling. it is extremely important when the disk suddenly seizes. If there is no such coupling, any jamming will lead to a back strike, with all its unpleasant consequences. This part is structurally made in the form of two disks. Normally, they are very close to each other. Slowing the stop of the rotor shaft allows you to significantly reduce the load that occurs during such an emergency. As a result, the total resource of the angle grinder is used more efficiently.

It is very convenient to remove and replace a disk on modern angle grinders thanks to a special button. When it is pressed, the planetary gear gear is rigidly fixed. A cylinder-shaped nut helps secure grinding wheels for normal operation. A special key, usually included in the delivery kit, helps to work with it. To start the engine and smoothly start work, one more button is provided. Some angle grinders can also adjust spindle speeds and prevent overloads.


As it is easy to understand from this description, the angle grinder device is quite simple in technical terms. And you can almost always find the cause of a malfunction with your own hands, without contacting service centers. It is appropriate to start by evaluating the performance of the brushes. In a normal situation, they should spark, evenly and moderately. If there are a lot of sparks, or, conversely, not at all, the electric brushes must be replaced as soon as possible.

One of the common reasons why the angle grinder does not turn on is just a break in the network cable — along the entire length or at the input. It is such an assumption that should be put forward when faced with a problem. Before disassembling the mechanism, it is necessary to check with a multimeter or a simple indicator screwdriver whether there is voltage. It is also recommended to make sure that there is electricity in the house (apartment). If voltage is present, but the device still does not work, check the electric motor. His most serious faults are the following:

  • short circuit between adjacent turns;
  • breakage of individual turns of the anchor or stator;
  • burnt collector lamellas.

Problems with the anchor are detected by such three characteristic features as:

  • noticeable heating of the case;
  • typical burning smell;
  • amplification of sparks on the collector.

In some cases, an external examination is enough to confirm the assumption of problems with the anchor. In this case, it is found that the windings are darkened, and the plates are burned out or delaminated. But it is worth considering that the visual manifestations of the problem are not always found. To determine the real cause of the failure, you will need to check with a multimeter. The device is switched to a resistance of 200 Ohms and successively assesses what resistance between pairs of adjacent lamellas. normally it should match.

But the resistance in the area from the lamellas to the anchor hull should be infinite. On the stator windings, the conclusions are checked, the resistance between these conclusions and the housing is evaluated. A standard multimeter does not allow finding interturn closures of stators and anchors. Only devices of a special type confidently solve this problem. Sometimes, if the angle grinder does not start, the whole point is in disrupting the operation of the button. When its contacts are covered with dust, they quickly collapse from overheating. The test is carried out, as in the previous case, with a conventional multimeter.

Important! Quite rarely it is necessary to encounter problems with the speed controller and a capacitor that suppresses interference.

With regard to mechanical deformation, it is mainly necessary to deal with wear or permanent destruction of bearings.

This defect is manifested in the following:

  • increased noise
  • vibration on the case;
  • severe overheating of the surface.

Failures in the operation of bearings (wear) can be assumed not only when the housing is heated. Any owner of angle grinders knows exactly how intensively the device is used. With a significant, systematically appearing load, the gears or gear teeth may well break faster than other parts. It is very important to inspect the problematic part. Then it will become clear whether its repair is possible or not.

Video: How to Check Stator Angle Grinder with a Multimeter

Quite a few people are faced with a problem when the angle grinder does not gain momentum, that is, it does not develop the full necessary power. First of all, it is necessary to check in such cases whether the block itself regulating the torsion intensity is working. And also it is necessary to assess the condition of the electric brushes and brush holder springs. Do not discount the speed drop due to a breakdown in the power cable (from frequent bending, from hitting a circle).

It is not difficult to determine whether a contact is of good quality. with its violations, the insulation of the wire becomes overheated. Of course, you can only feel it after turning off the angle grinder. In order not to waste time on unnecessary checks, you should think about what could cause such a failure. If problems arose after repair, you can still assume errors during reassembly. Usually, then, disturbances in the power supply of the motor or in its windings are accompanied by strong vibrations.

In some cases, the angle grinder does not unscrew the nut. Basically, this trouble occurs on angle grinders with a disc of 150 mm or more. Increased torque increases the likelihood of tightening the nut to the limit. If inertial forces are relatively small, such a danger is also less likely. Damage to the stopper, as well as the situation when the disk is bitten, are easily recognized even without special knowledge, therefore, no additional comments are required.

DIY repair

It’s not enough to identify problems. you should also know how to fix them. To unscrew the same nut, if the standard wrench does not help, you need to use a rod. It is inserted into the holes, then they try to move the fasteners in the right direction with the hammer blows. But you need to strike very carefully to avoid breaking the button. Often there are recommendations to heat the nut itself. The most gentle method involves breaking off the edges of the disk until the problem hardware. Next, you will need to choose the following elements:

  • relatively thin steel plate;
  • spare angle grinder with its own disk;
  • just a thin disk.

Damaged disk is drained. But its fixing fasteners are undesirable. The procedure will take a maximum of 5 minutes.

serious problems sometimes require completely disassembling the angle grinder. It is worth sticking to the following sequence:

  • first remove the disk holding nut;
  • then remove the bolts securing the protective cover;
  • after them comes the turn of the bolts on the housing and in it;
  • further, remove the top of the back of the case and twist the bolts securing the cord;
  • both cables and buttons must be removed from the grooves; individual models come with a monolithic back of the case, which is removed only completely;
how to check the stator angle grinder with a multimeter
  • now you can change the engine. first disconnect its wires, remove the brushes, and then separate the gear from the outer casing with an angle grinder; without this manipulation, it will not be possible to pull out the anchor of the electric motor;
  • next, remove the device that draws air and the bolts pressing the stator to the housing, as well as the contact spring rings attached to the stator wires;
  • the stator itself is taken out after careful blows with a mallet on the ribs, otherwise it will not budge;
  • the next step in disassembling is removing the gearbox bolts and removing it itself.

Assemble in the reverse order. It must be remembered that the casing of the part of the angle grinder is not screwed on, but latches. Its removal is very simple: you only need to rotate the cutout at an angle of 90 degrees to the tool. Return the casing into place, turning it back until it clicks.

You can repair the angle grinder in more complex cases. For trained people, even rewinding at home is not a particular problem. It will only be necessary to prepare an enamel wire and electrical cardboard. The process is as follows:

  • first, the winding and former insulation are removed from the housing;
  • Further, they examine the grooves. if the coils burned, the insulation is inevitably burnt;
  • part of the material is fused to the body. these layers need to be cleaned with a file or a diamond drill; leaving them in place, they risk damaging the new winding;
  • wires can be separated only after burning the insulation with an open fire;
  • then one of the wires is measured with a micrometer; now it is very easy to determine the number of turns;
  • further, they take any wire from which they make a loop placed in the grooves of the stator; in accordance with its diameter, a cylinder is chosen, which will serve as the basis for winding;
  • an enamel wire is screwed onto the base;
  • the front parts are connected with thick technical threads; it is better to do this with a glass tape, since it will not tear and melt;
  • shrink cambrics are put on the edges that are still free;
  • electrical board will make it possible to make sleeves; inserting these sleeves into the grooves, place windings in them;
  • further, the resistance is accurately measured with a multimeter;
  • impregnation with varnish will eliminate vibration and mutual friction of the wires;
  • Connect devices only after the varnish has dried.

Sometimes it becomes necessary to change the direction of rotation of the angle grinder. Normally, it should spin just so that the sparks fly towards those working with the tool. Yes, overalls will deteriorate faster. However, in the event of an emergency, the nozzle will fly forward and do no harm. Therefore, you can reconfigure the device only if the sparks fly "from the operator."

Precautionary measures

The use of an angle grinder must be carried out in strict accordance with the instructions and safety requirements. The same rule applies to repairs. The following precautions should be followed:

  • categorically it is impossible even to carry out diagnostics, not to mention the replacement of individual parts if the device is connected to the mains;
  • when removing the bearings, care must be taken to ensure a reliable stop;
  • only parts made of soft metals are used for knocking out parts;
  • it is impermissible to press in new bearings by direct hammer blows; you can only beat on the tube, which will push the parts to the desired position;
  • after dismantling the bearings, they are thoroughly cleaned and grease removed; remove all, even minor contaminants, by washing with alcohol;
  • to eliminate errors, they must be checked after assembly for any backlash.

Care and proper operation

To keep the tool working and its own health, you should use the angle grinder only for those works for which it is intended. It is worth paying attention to the following rules:

  • you can not use any lubricant, any spare parts, except those recommended by the manufacturer;
  • all companies warn in their instructions that working with angle grinders is possible only with good health; even ordinary fatigue, not to mention alcohol or drug intoxication, is a serious danger;
  • no work should be carried out if the protective cover is removed;
  • all the time you should control the location of the wire. it should not fall under the cutting or grinding disc;
  • checking the technical condition of the tool should be carried out before the start of work, and after its completion; it is advisable to inspect the angle grinder also after long (from 1 hour or more) breaks;
  • regardless of make and model, it is necessary to disassemble the tool from time to time, cleaning out all impurities from it, updating the lubrication of the chassis;
  • you need to remember that the angle grinder is not designed to work and even to store in high humidity conditions;
  • it must always be put in such a way that the tool does not fall accidentally, is not subjected to pressure from heavy objects; it is worth remembering that the cord should not hang down;
  • minimize folding and twisting of the cable;
  • It is absolutely unacceptable to transfer the angle grinder to the network wire or pull it towards you;
  • the disk and other nozzle are selected strictly for the work that they are going to do;
  • in the event of a crack, or even single potholes, the circle must be replaced immediately; the same should be done with disks that are irregular in shape;
  • when the lap is replaced, it starts for 30 seconds in trial mode; if during this time no unusual noises, vibrations or beats are noticed, everything is in order;
  • Do not leave anything in the work area that could easily catch fire, become very hot or explode;
  • work only with good lighting on a stable platform (support);
  • you cannot hold workpieces in your hands. they are either clamped in a vice, or instructed to hold someone with adjustable wrenches.

Important! Compliance with these simple rules allows you to avoid injuries and extend the time of use of the angle grinder, delaying repairs.

See how to repair an angle grinder with your own hands in the next video.