How To Check The Rotor Of An Angle Grinder With A Multimeter

Checking the armature and stator at home

How to check the anchor of an electric motor is NOT a suspension of what kind of engine you have. All this is done

The stator of the angle grinder will also please you more with the prerequisite for the failure of the power tool.

Checking contacts with a light bulb

If there is no tester, you can get out of the situation with a simple 12 volt light bulb. The power can be any, optimally 30-40 W. The voltage from the 12 volt battery must be applied to the plug of the angle grinder, inserted a light bulb into the break of one wire. With the armature working properly, if you rotate the spindle by hand, the light should be on, and not changing the brightness. If the glow changes. This is a sure sign of an interturn short circuit.

If the light is off, then this may indicate the following:

  • The brushes may hang in the inoperative position. The retaining spring has worked.
  • There was a break in the supply circuit.
  • There was a short circuit or break in the stator winding.

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

Indicator as a way of checking turns in case of short circuit

Manufacturers assemble the angle grinder in different ways, so some do not see the wires that connect to the manifold. The insulation is well hidden under a bandage or opaque compound, and to check its serviceability, you can use the indicator of short-circuited turns. The device is easy to use and small in size.

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To determine the short circuit, a diagnostics for the absence of open circuits is first carried out. To do this, you need a tester to measure the resistance between the lamellas. The resistance reading should NOT be more than half if this is the case. That is, a cliff. When the norm is displayed on the monitor, go to the next stage.

The resistance measuring device has a sensitivity adjustment function, which is also used for diagnostics. We look at two bulbs and adjust the instrument so that the red lights up. We apply the indicator to the winding, while the anchor is slowly steep. If the light is on, it indicates a short circuit.

Visual inspection from outside

Troubleshooting should start 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 outlet.
  • Using the voltage indicator, check that the current flows to the motor manifold and the start button.

Solution to the problem

This type of diagnosis is rather complicated. You must have the skills to work with a multimeter, as well as be able to disassemble the angle grinder.

If your tool suddenly stops working, then it is better to immediately go to the workshop:

  • Even if you make sure that it was the anchor that was out of order, and establish the cause of its breakdown, you are unlikely to be able to replace it or repair it yourself. You still have to carry the tool to the workshop;
  • If the tool is still under warranty, opening the angle grinder by yourself may void the manufacturer’s warranty.
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To ensure long tool life, choose products from renowned companies with extensive experience in the industry. Also, follow the rules for operating the tool, because very often they fail for this very reason.

See also:

Tips in the article “Open wiring in the interior” here.

Checking the motor armature, how to check the angle grinder:

Replacing the anchor yourself at home

Practice shows that if it is decided to replace the armature of an angle grinder, then it is best to change it together with the support bearings and the engine cooling impeller.

Replacement will require:

  • New anchor angle grinder. Must match your model. Interchangeable with other models. Unacceptable.
  • Screwdrivers, wrenches.
  • Soft brush and cloth for cleaning the mechanism.
How To Check The Rotor Of An Angle Grinder With A Multimeter

Winding repair

Anchor rewinding angle grinder. Work that requires the right skills and extreme precision. To achieve the best end result, it is worth contacting an Appropriate Specialist.


Short-circuited turns indicator. Used for diagnostics of closed anchors. This type of rotors is characterized by the lack of access to the junction of the winding with the lamellas. The tester has two LEDs. Red and green. By rotating the armature connected to the tester, you can determine the presence of a breakdown in the winding by the lit red LED.


Observance of precautionary measures guarantees the serviceability of all units of the angle grinder during a long period of operation:

  • Avoid overheating of the electric motor, graphite brushes, and do not exceed the permissible load on the grinder;
  • Use replaceable cutting wheels of the appropriate diameter;
  • Prevent dirt, sand, moisture and foreign objects from entering the angle grinder body;
  • Monitor the condition of the lubricant in the gearbox and bearings. Its lack or burnout will lead to an increase in the load on the electrical part of the instrument;
  • Avoid working in an overloaded network, for example, when the welding machine is running.
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12 volt bulb

Connect two wires to the contacts of the light bulb. Make a break in one of them. Connect the wires to the power source, put the edges of the “broken” wire on the lamellas so that they do NOT touch each other. Rotate the anchor. If there is no breakdown in the winding, then the light will be on continuously.

Collector repair

If structural damage to the collector lamellae is found, they must be pierced. This can be done on a lathe or using improvised means. The groove must be uniform. Otherwise, the balancing will be disturbed, which will entail the destruction of the graphite brushes during operation and the failure of the second units of the angle grinder.

Breakdown reasons

Angle anchor grinder. The rotor is a part that is subjected to the greatest stress: temperature, mechanical and electromagnetic. Violation of the operating rules prescribed by the manufacturer leads to an early failure of this unit. Some of the factors behind these violations are:

  • Going beyond the acceptable time of continuous work;
  • Lack of protection against aggressive environments. Dust, sand, dirt, moisture;
  • Exceeding the load parameters;
  • Mechanical damage;
  • Work at the time of voltage drops.

These reasons can lead to the following armature malfunctions:

  • Melting of the insulation (insulating varnish) of contacts or windings as a result of overheating;
  • Mechanical damage: scratches, chips, cracks, from contact with foreign particles, getting into the compartment with moving parts;
  • Breakdown at weak points of the winding caused by overload;
  • Curvature or imbalance of the anchor shaft;
  • Short circuit or carbon deposits on the lamellas.