How to check the angle grinder armature with a tester

How to Check an Angle Grinder Armature with a Tester

When diagnosing and repairing the electrical part of the angle grinder, it is most convenient to use a multifunction tester (shortened name. multimeter). If you do not have such a device at hand, then for some checks will work a screwdriver with an indicator or a light bulb with two wires. In the repair process, the multimeter can measure both the values of voltage and current, and resistance of the motor windings. The indicator and the bulb can only indicate the presence or absence of voltage.

Failure of power supply

Perhaps the most common electrical malfunction of the angle grinder is the breakage of power wires inside the power cable sheathing. To diagnose and repair such damage, simply disassemble the back handle of the angle grinder and check the voltage at the terminals in front of the switch. Another way is to disconnect the cable terminals and use a multimeter to check the resistance of each wire for interruption.

Check and Rewind Stator

To check the stator of an angle grinder motor, disconnect both of its windings from the supply circuit, and then measure their resistance with a multimeter in the range of 200 ohms. On a good winding the device will show a resistance of about one ohm, and on a faulty (with a break). tens or hundreds of ohms. If the winding has failed as a result of a short circuit, soot can usually be seen on the inside of the stator housing. Check the stator for interturn short circuit with an ordinary tester is impossible. there are special inductive devices for this purpose. The only way to repair the stator is to replace or rewind it. The second is only possible if you have the appropriate skills, so most often the stator is simply replaced.

Armature diagnosis with a tester

Check the angle grinder armature should be checked both for winding breakage, and for their short circuit to the core. In the first case, the resistance is measured in the circle between two adjacent plates of the collector, located on the rotor shaft. All values should be the same (within one ohm) and a significant difference indicates a breakage. The second involves measuring between the rotor coil and the collector plates. To find the inter-turn short circuit, as in the case of the stator, it is necessary to use a special device. If a fault is detected, it is necessary to decide how to repair it: by rewinding the armature or replacing it with a new one. Independently rewind the armature windings without the appropriate skills and equipment is unrealistic, and rewinding in the service will cost almost as much as a new armature. Therefore, the best repair option is to buy and independently replace the anchor.

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Checking the starter and control unit

Diagnosis of electronic components of angle grinder comes down to determining the serviceability of individual blocks, and repair (if no skills in radio engineering). to their complete replacement. The soft starter can be checked with a dial ammeter, comparing the current spike with and without. For an accurate diagnosis of the block to maintain the speed under load requires an oscilloscope. Although in order to understand whether it is faulty in principle or not, it is enough just to observe the behavior of the angle grinder at different modes.

Checking carbon brushes

Carbon brushes wear out during operation and must be replaced when they reach their minimum size. The first sign of brush problems is an irregular spark ring around the collector with flashes. Some models have round openings in the housing with screw caps for replacing or checking the brushes. But for most grinders in order to change them, you have to completely disassemble the housing or the back handle, just like during the repair.

Diagnose the start button and speed regulator

The most common malfunction in the electrical angle grinder is the failure of the starter button, which is most often the result of getting dust in it. You can check the working order of the button with a multimeter or a screwdriver, by measuring the voltage at its output contact. It is not usually repairable and is simply replaced with a new one. Speed regulator defect is even easier to diagnose: when you rotate the wheel it either changes rpm of the spindle or not. If you are not skilled in repairing such devices, it is easier to buy a new one for a few hundred.

Checking the rotor of an angle grinder using various methods

Some people test an inoperative tool with a tester. Sufficiently correct solution to the problem, but in this case, this measuring device, unfortunately, can not show us much.

It should be understood that the armature of a small motor of a construction tool, has a winding and a magnet wire, where the shaft of rotation is located. One end terminates in the drive gear, the other ends in a manifold with lamellae. The magnet wire has soft plates and grooves that are coated with a special coating for insulation.

Armature and field call testing. Makita angle grinder repair ( M0900 )

As the internal diagram of the rotor shows, in the grooves of the part there are conductors of the anchor winding, there are two. Each of them is half a coil, the edges of which are connected in the lamellae in pairs. In one groove are placed: the first coil (its beginning) and the last coil (end), which are shorted to one lamella.

So, how to check the armature of an angle grinder? Rotor malfunctions can happen only in some cases and for the following reasons:

  • Breakage of conductors;
  • Short circuit between coils;
  • Insulation breakdown. In this case, the winding is shorted to the metal armature base, in most cases this failure is caused by a violation of the insulating winding of the conductors;
  • Collector lead unsoldered;
  • Unevenly worn collector.
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If the armature is defective, it leads to motor overheating, which melts the insulation shield, the result. a short circuit of the turns. Further, the contacts that serve as a connection between the rotor winding and the collector plates are self-soldered. Current stops flowing and tool motor does not function.

The angle grinder’s stator can also be the cause of power tool failure.

Ways to test and diagnose

How to check the rotor of an angle grinder for performance? It is necessary to check the place of motor failure in case of malfunction, because this procedure will help to understand which part of the mechanism works and which part does not work any more. Diagnosis is made in several ways:

Sometimes even a visual inspection is enough to know that a short circuit has occurred. The part in this case will show, for example, an unprotected winding, wires where the insulation is melted

It is also worth paying attention to the charred varnish or its smell after overheating the engine

Contact disturbance is also caused by dust (graphite from the brushes) collecting on the lamellae. It is as easy to spot as it is to clean this fine debris from the armature.

A device called a “multimeter” also helps determine the breakdown of an electrical appliance. It is enough to set the resistance to 200 ohms and put the probes on two adjacent lamellae. The resistance between all the plates is the same if the part is working properly. If it is less than 1 ohm it is a short circuit. When the indicator is greater than one. this means a breakage of winding turns. The device may even go off-scale, because the resistance in the latter case can be very high. Using an analog multimeter the needle will swing to the right all the way, the digital measuring instrument will not show anything.

Multimeter, in fact, is the same tester, which determines the resistance in the right places of the electric tools.

When there is no device to determine and calculate the resistance, you can use a simple 12 volt 40 watt light bulb. Connect two wires to the bulb. Where there will be a minus, we need to make a break. Then we apply the voltage. We put the ends of the wire at the breakage to the manifold plates and twist it. When this manipulation, the light bulb lights up without changing brightness, there is no short circuit.

Another method of testing concerns the breakdown of current on the ground. To do this, connect one wire to the lamellae and the other to the armature iron. After that we perform the same manipulation with the shaft. If there is a malfunction in the part, the light will be on.

Rotor malfunctions

In case of optimum use, the rotor will not wear out. Routine maintenance is carried out by replacing the brushes when they are worn. But over time, with heavy loads, the stator gets hot and soot builds up. The most common mechanical failure is bearing wear or misalignment.

The angle grinder will work, but the plates will wear out quickly and the motor will break over time. To avoid damage, the tool must be inspected and the operating conditions maintained.

Moisture on metal will cause rust. Increases the friction force, requires more current to operate. There is considerable heating of contact groups, solder, there is a strong spark.

Visual inspection of breakage

Every tool, even the best quality one, is subject to breakage. Particularly if it is used intensively. If the angle grinder breaks down, you are unlikely to be able to repair the tool yourself. But a preliminary inspection can also be made without special skills.

The armature is the most common cause of damage. The breakage may be mechanical. Visual inspection will show uneven wear of the brushes, as well as their burning. In addition, if the armature is faulty, the angle grinder will vibrate and heat up.

There are electrical breakdowns. These include:

Such faults can be detected with special meters, for example, a multimeter.

How to Fix an Angle Grinder For Beginners, How to check Armature, Stator, Carbon Brush, Switch

Checking with a Short Circuit Current Indicator (SCII)

You may find some armatures that have wires connected to the collector that are not visible because they are sealed with opaque compound or because they have a bandage. That’s why it’s hard to find commutation on the collector in relation to the armature. The Short Circuit indicator is an aid.

This tool is small and easy to operate.

First check the armature for breaks. Otherwise, the indicator will not be able to detect a short circuit. Use a tester to measure the resistance between the two adjacent blades. If the resistance is at least twice the average, then you have a break. If there is no breakage, go to the next step.

Resistance adjuster allows you to select the sensitivity. It has two lights: one red and one green. Adjust the control so that the red light comes on. On the body of the indicator there are two sensors in the form of white dots, located 3 centimeters apart. Apply the gauge to the winding. Turn the armature slowly. If the red light comes on, it means that there is a short circuit.

How to check the angle grinder armature for malfunction

If the armature is faulty, the motor overheats, the winding insulation melts and the turns are short-circuited. Solder the contacts that connect the armature winding to the collector plates. Current stops flowing and motor stops running.

How to check the armature if you don’t have special tools

If you can not use special devices, you can check the contacts with a 12-volt light bulb. It is inserted into the gap, then the battery voltage is applied. If there’s nothing wrong with the armature, it will light up and stay lit.

If the light does not come on, then you need to look for a broken circuit or short in the stator.

How to check the rotor of an angle grinder with a light bulb

  • Take two wires and connect them with a lamp.
  • Make a break in the minus wire.
  • Apply voltage to the wires. Put the ends of the break on the collector plates and twist it. If the bulb stays on without changing brightness, there is no short circuit.
  • Do a short-circuit test on the iron. Connect one wire to the lamellae and the other to the rotor iron. Then to the shaft. If the bulb stays on, it means there’s a ground fault. The winding is shorted to the rotor housing or shaft.

This procedure is similar to the multimeter diagnostics.

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Asynchronous motors

Induction motors are widely used not only in industry (machines, compressors, pumps), but also in everyday life (in refrigerators, washing machines of some models). If they malfunction, visual inspection should begin with the stator windings, which act as an armature.

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Before testing the armature of the electric motor, it is necessary to check other units and parts (as the cause may be in their damage). connection cables, magnetic starters, thermal relay, capacitor, as well as to check the presence of voltage. If all is normal, check that there is no power supply and disassemble the motor.

Causes of stator windings that stop working are most often the following:

If the inspection does not reveal any faults, further diagnosis is carried out with a multimeter. On 380V machines, which are wired in delta or star connection, each winding is checked individually. Their resistance values should not deviate more than 5 %. Then the windings are tested against the frame and against each other. The resistance should tend to infinity, other indications are that there is a breakdown of the windings between each other or to the frame. This problem can be solved by a complete rewind.

For 220 V motors it is enough to test the operation winding and the starter winding. The resistance of the first winding should be one and a half times lower than that of the second one.

The most difficult stage of the check-up is the search of the inter-turn short circuit, since the visual inspection does not reveal it. Use a special inductance meter. If all the windings have the same value, there is no problem. The lowest value on any of the windings indicates that it is damaged.

Winding insulation resistance is checked with a megohmmeter for 1000 V, which is connected to a separate power supply. One wire is connected to the body of the unit in a place that is not painted, the other. to each terminal of the winding in turn. The value must be greater than 0.5 megohms; a lower reading indicates that the motor needs to be dried. Avoid touching cables and be extremely careful when testing. To avoid accidents, de-energize the motor and strictly observe all safety precautions.

Now you know how to check the motor armature with a tester and you can identify the cause of failure without calling a specialist and fix it, saving money and time.

How to test a motor with a multimeter

The most common household electrical measuring device is a multimeter. Use it to test for continuity of windings and absence of earth fault.

The start winding and the run winding must be tested. And the inrush resistance will be 1.5 times more than the working one. Some electric motors will have a starting winding and a working winding that share a third lead. Read more about this here.

For example, a motor from an old washing machine has three leads. The higher resistance is between the two points of the 2 windings, e.g. 50 ohms. If you take the remaining third end, this will be the common end. If you measure between it and the 2nd end of the starting winding, you will get about 30-35 ohms, and if you measure between it and the 2nd end of the working winding, you will get about 15 ohms.

For 380-volt motors connected by a star or delta circuit, you will need to take apart the circuit and wire each of the three windings separately. Their resistance should be the same from 2 to 15 ohms with a deviation of not more than 5 percent.

Be sure to test all windings between each other and to the frame. If the resistance is not great to infinity, then there is a breakdown of the windings between themselves or on the body. These motors should be sent to a winding service.

How to check the insulation resistance of the motor windings

Unfortunately, you can not check the insulation resistance value of motor windings with a multimeter. For this purpose, you need a megohmmeter for 1000 volts with a separate power supply. The device is expensive, but every electrician at work who has to connect or repair electric motors has it.

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

How to Find a Short Circuit

The most difficult thing is to find the inter-turn short circuit, in which only a part of turns of one winding is short-circuited. Not always detectable by external inspection, so for this purpose a 380 volt motor inductance meter is used. All three windings must have the same value. If there is a short circuit between the coils, the inductance of the damaged coil is minimized.

Common problems in operation of the angle grinder

The angle grinder is a fairly unpretentious tool, because it is suitable for heavy loads. к. designed for heavy loads and dusty environments. The main problems in its operation in most cases are related to improper use, as well as failure to comply with the timing of maintenance and scheduled repairs. The following faults are the most common:

  • The angle grinder does not turn on. The most common cause of this phenomenon is a wire breakage in the power cable or a faulty switch. And in electronic controlled grinders. failure of the speed control unit or soft starter.
  • the angle grinder operates at low speed. This is usually caused by a short circuit in the rotor winding or an electronic malfunction.
  • The angle grinder gets very hot. Not uncommon because of improper ratio of recommended work cycles and breaks. The heat can also be caused by poor engine cooling due to dust accumulated inside the housing.
  • angle grinder sparks. In this case the main reasons are abrasion of carbon brushes or wear of the electric motor collector. Brushes also spark if the collector plates are extremely dirty or oxidized.
  • angle grinder is smoking. This is normally caused by excessive use and by the air cooling ducts becoming clogged with dust. Short circuits in the rotor or stator windings may also be the cause of the tool smoking.
  • angle grinder buzzes but does not rotate. This usually occurs if the gearwheels jam or the bearings are damaged.
  • The spindle locking button is defective. This is caused by dust entering the retainer, which causes wear on the rod.
  • The bearings are broken. Bearing failure most often occurs after prolonged use and use with shock loads.

The clamping nut is another very common problem with most floor saws.

Diagnosis with an armature test tool (choke)

Armature test tool to detect the presence of winding short circuits. A choke is a transformer that has only a primary winding and a magnetic gap cut out in the core.

When we place the rotor in this gap the armature winding begins to work like the secondary of a transformer. Turn the machine on and place a metal plate, such as a metal ruler or hacksaw blade, on the armature. If there is an inter-twist fault, the plate will vibrate or be magnetized to the armature body due to local iron oversaturation. Rotate the armature around its axis, moving the plate so that it lies on different coils. If there is no short circuit, then the plate will move freely along the rotor.

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Types of breakdowns in angle grinders

Typical minor malfunctions

In the case of a malfunction, it is necessary first of all to exclude elementary breakdowns:

check, angle, grinder, armature, tester
  • The angle grinder does not turn on. The angle grinder suddenly became defective. it stopped turning on. In this case, you need to check the serviceability of the socket, then the plug and the power cord, perhaps just the drive does not work because the product does not get the current.
  • The cable and plug are intact, but the drive does not work. You need to check the start button. Angle grinder switch repair is easier to do by buying a new button and replacing it. Because it is rarely repairable. mainly the plastic pull rod of the switch is broken inside. If you want to experiment, you may disassemble it, number the pins and put it back together again in order to avoid a short circuit after reassembly.
  • The above parts are unharmed, and the angle grinder does not want to work. then it’s time to check the brushes. It may be time to change them in the angle grinder. Brushes are constantly heated from work, so they wear out quickly and need to be replaced more often than other parts, and in pairs.

Significant faults

Having excluded all the minor malfunctions, it is necessary to understand why the tool does not want to turn on, and how to repair it. Most likely the problem is serious and requires additional knowledge. This happens in cases where:

  • The housing is deformed;
  • One of the bearings has jammed;
  • The armature or stator does not work;
  • The gear wheel teeth are broken or frayed;
  • The manifold has failed;
  • The sensor of the control electronics shows no signs of life.

If it is determined that the failure occurred in the mechanical part of the angle grinder, then you need to pay attention to the condition of the large gear that is on the shaft, and on the bushings. If the teeth are worn out partially or the shafts wobble, they need to be replaced immediately.

The most common breakages

Malfunctions of the angle grinder occur quite often. Everyone who works with this tool knows about it. What fails most often?

check, angle, grinder, armature, tester

The spindle lock knob is broken.

A single uncomfortable press on the spindle locking button while the disc is turning will cause it to break. Sometimes it can be broken if it is used to remove a jammed disc. To prevent this from happening, you must use an open-ended wrench inserted into the special holes near where the disc is mounted.

Breakage of the gear teeth

Mostly it occurs when there is jamming. If you can hear a rattling noise in the gearbox, it is a sign of this malfunction. When more than one cog is broken, the angle grinder will not be able to cut the desired material.

To keep the tool in operation, all gears and the bevel gear have to be changed. Before you go to the store for parts, remember the manufacturer, model and capacity of the product.

Electric motor does not work.

This type of failure occurs with the angle grinder, which work in places where a lot of dust, and when they are given a rest, they leave on the ground. Dust that gets inside spoils the winding. High loads, especially for a small angle grinder, result in motor failure.

If the angle grinder is used for cutting materials that create a lot of dust, then it is recommended to cover the ventilation holes with something.

The bearing fell out

The weakest link, and not only in angle grinders, is the bearing. High frequency of rotation quickly wears out the mechanism. The good news is that it is easy to replace the bearing. Replacement sprinkled bearing in the angle grinder, should be done in time to avoid a breakdown that can not be fixed.

Stator malfunction

it is easy to spot it, if the angle grinder has started, but the disc speed is too high and differs from normal operation. it means there is a short circuit in the stator winding. Stator breakage is considered the most serious and requires special skills to repair. When in your power there are doubts, it is better to turn to professionals, so then do not have to buy a new tool.

If the decision to repair it yourself is made, it begins with the cutting of the front parts of the winding, the remains are all removed. The next step is to make a new winding according to the template. It must be identical in the number of turns, with the same density and made of wire of the same thickness as the previous one.


angle grinders with a power less than 1100 W are usually equipped with spur gears. They are on the stator. grinders with higher power have helical gears. Each of the variants has a cone shape, the gear rod of the angle grinder is crossed with the stator shaft at an angle.

Repair of the gearbox of angle grinder is mainly replacement of gears. If the disc gear breaks, it is difficult to replace it, because it is very firmly fixed. It is not difficult to disassemble the gearbox:

  • It is necessary to unscrew the nut from its side;
  • gently take the rotor housing in a vise and with light strokes knock out the gear housing;
  • change the position of the clamped rotor and knock out through a wooden board bearing;
  • unscrew the pinion from the shaft.

speed regulator

Not all angle grinders have a speed regulator. When the angle grinder is used for cutting, in principle, it is not necessary, but if grinding is carried out, it is simply necessary. If it suddenly stops working, it is likely to have burned out the board, which must be removed and bought the same one in a power tool store for further replacement.

Self-repair of angle grinder is not always feasible. If something suddenly fails or is not clear, it is better to contact the service center.

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