Method for Judging the Quality of Electric Motors with a Multimeter
There are three-phase motors and single-phase motors, and single-phase motors also have three and six wires.
Three-phase motor
Six taps for the three-phase winding of a three-phase motor. Let's first remove the connecting piece connecting the motor terminal. Measure the start and end of each phase winding with a multimeter to see if it is on or off. Then use a multimeter to measure the resistance value between each two phase winding separately, at least greater than 0.5 megohms, the greater 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 judged.
Three wire single-phase motor
A unidirectional motor only has 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-wire 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 electric motor also has 6 terminals, so its connecting pieces need to be removed as well. 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 for three-phase motors.
Using a multimeter to judge the quality of a motor can only be a preliminary judgment. The insulation resistance between windings and the insulation resistance of each phase winding to ground should be measured with a megohmmeter to be more accurate.
There is also a short circuit between the turns of the winding that cannot be measured, and we can only use comparative methods to guess whether there is a phenomenon of inter turn short circuit. For example, if the organization of a certain phase winding is much smaller than that of other two phases, we can suspect that it has an inter turn short circuit.
