How to use a multimeter to judge whether a motor is good or bad
There are three-phase motors and single-phase motors, with single-phase motors having three wires and six wires.
Three phase electric motor
There are 6 taps on the three-phase winding of a three-phase motor. Let's first remove the connecting piece that connects to the motor terminal. Measure the starting and ending ends of each phase winding with a multimeter to see if it is open or closed. Then use a multimeter to measure the resistance value between each two-phase winding separately, which should be at least greater than 0.5 megaohms, the larger the better. Finally, measure the insulation resistance between each phase winding and the motor casing, which should also be infinite. By measuring in this way, the quality of the three-phase motor can be basically determined.
Three wire single-phase motor
A unidirectional motor has only two windings, one for starting and one for running. One of the three wires is their common wire, which means that one end of the two-phase winding is connected together. The other two are the other taps of the two-phase winding.
The resistance between the two taps should be the maximum 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 casing to see if it has been broken down. The higher the resistance, the better, and the lowest is the same, not less than 0.5 megaohms.
6-line single-phase motor
The reason why there are 6 lines is that there are actually two lines (Z1, Z2) that are centrifugal switch lines. This type of motor also has 6 terminals, so its connecting pieces need to be removed. Remove the capacitor as well, and then measure the resistance values at the beginning and end of the two-phase windings, as well as between the two-phase windings. The method is the same as that of a three-phase motor.
Using a multimeter to judge the quality of an electric motor can only be a preliminary assessment. The insulation resistance between windings and the insulation resistance of each phase winding to ground should be measured accurately using a megohmmeter.
The short circuit between turns of the winding cannot be measured, so we can only use comparative methods to guess whether there is a phenomenon of short circuit between turns. For example, if the organization of one phase winding is much smaller compared to the other two phases, we can suspect that it has an inter turn short circuit.
