How to Quickly Test Angle Grinder Rotor for Breaks or Short Circuits with a Device

how can you quickly check whether the rotor of an angle grinder is damaged (i.e. how to determine whether it has a break or a short circuit? is there any device that can quickly and efficiently determine this?

A special electromagnet is used for this purpose. A magnet is placed on the rotor and it rotates slowly. A thin plate is placed on top and if it starts to shake, the rotor has a winding short circuit.
Another method is to supply alternating current with a voltage of a few volts through a commutator (but usually not on opposite sides of the commutator but at an angle of about 120 degrees - I have no idea if it matters much). The current is observed on a pointer meter - if there are current anomalies (large differences), the rotor is damaged.

The second method is supposedly better, but if you don`t know anything about it, it`s better to go to a specialized facility.

Hello
If you do not have this magnetic device at hand, take a regulated power supply with a capacity of about 1A, connect the power supply cables to the adjacent sections (terminals) of the commutator, set, for example, 1A and check the adjacent commutator terminals 1z2, 2z3, 3z4, etc., etc. You should obtain similar values of the current flowing through the windings rotor. If somewhere there is significantly less, it means that it will need to be rewound.
Regards

In AC commutator motors, 95% of all damages are rotor damage, the rest are the brush holder-brush system and the stator. If the engine power is several hundred Watts, the rotor can be checked with an ohmmeter. Before checking, it is advisable to clean the spaces between the commutator sections (this is best done with a saw blade, grinding its teeth first, or with a hair saw). The resistance between individual sections of the commutator should be within 2-3 Ohm. If it is close to zero it is suspicious. The second method is as written by colleagues above, using an electromagnet. The next method: measure the current consumed by the motor - it should be lower than the rated current. Damage can also be detected by observing the operation of the motor. The brushes create an electric arc (too high current density per millimeter) across their entire width. If there is a gap, the arc is point-like and extends from brush to brush.
south

Yet another method. We connect constant voltage to the brushes so that the current is close to the rated current. Then, we use a direct current meter to measure the voltage between subsequent adjacent commutator divisions. When the rotor is good, the voltage is always the same. When there is a short circuit, the voltage will be lower, when there is a break, the voltage will be very high. This method is most useful when we do not want to disassemble the machine.

Thank you all for such comprehensive information