In part 1 of How to Test an Electric Motor, we talked about the importance of testing and different types of tests that you can perform. In part 2, we are going to talk about more of these tests and how you can put test data to good use.
Shaft Current Test
When you suspect that the motor bearings have suffered electrical damage, then you likely need to perform a shaft current test.
So how can bearings experience electrical damage? When capacitive coupling exists between the motors and the windings, it can create a voltage on the shaft that can be discharged through the motor bearings. When that happens, it leaves behind surface damage like pitting, fluting, and craters. This type of damage shortens the useful life of the motor bearings and can lead to premature motor failure.
You can detect and measure shaft voltage (and bearing currents that result from it) by either using an oscilloscope with special voltage probes or a shaft voltage tester such as the one made by Aegis . If you're wondering why you can't use a multimeter, it's because the voltages occur too quickly for it to capture. The oscilloscope, on the other hand, allows you to observe those changes over time despite this.