Methods for Judging the Quality of an Electric Motor with a Multimeter
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There are three-phase motors and single-phase motors. Single-phase motors can have either three wires or six wires.
Three-phase Motor
A three-phase motor has six taps for its three-phase windings. First, remove the connection pieces connected to the terminals of the motor. Use the continuity range of the multimeter to measure the start and end terminals of each phase winding to check whether there is continuity. Then, use the multimeter to measure the resistance values between every two phase windings respectively. The resistance should be at least greater than 0.5 megohm, and the larger the better. Finally, measure the insulation resistance between each phase winding and the outer shell of the motor, which should also be infinite. Through these measurements, you can basically judge the quality of the three-phase motor.
Single-phase Motor
A single-phase motor has only two windings, a starting winding and an operating winding. For a single-phase motor with three wires, one of the wires is their common wire, that is, one end of the two-phase windings is connected together. The other two wires are the other taps of the two-phase windings.
The resistance between the two taps should be the largest and equal to the sum of the resistance values of the two windings.
Of course, we also need to measure the resistance between the coil and the motor casing to check if it has been broken down. The resistance is, of course, the larger the better, and at the minimum, it should not be less than 0.5 megohm.
Single-phase Motor with Six Wires
The reason why there are six wires is that in fact, two of the wires (Z1, Z2) are the wires of the centrifugal switch. This kind of motor also has six terminals, so the connection pieces should also be removed. Remove the capacitor as well, and then measure the start and end terminals of the two-phase windings respectively, as well as the resistance values between the two-phase windings. The method is the same as that for the three-phase motor.
Judging the quality of an electric motor with a multimeter can only be a preliminary judgment. The insulation resistance between windings and the insulation resistance of each phase winding to the ground should be measured with a megohmmeter for more accurate results.
Moreover, the short circuit between turns of the winding cannot be measured. We can only use the method of comparison to guess whether there is a short circuit between turns. For example, if the resistance of a certain phase winding is much smaller than that of the other two phases, we can suspect that there is a short circuit between turns.
