Problem- Motor winding problem ?

[iyerks]

I have bought a set of 10 AC servo motors and drives from a Taiwanese company. One of the motors has suddenly died !

I mean it does not deliver any torque at all - we exchanged motors, drives, encoders, but the problem seems to exist in the windings - its encoders work fine on other motors, the drives are working fine with the other motors !

There are no alarm indications on the drive too - it seems the motor simply stops drawing current and delivering the torque it is supposed to give.

What could be the problem ? Any ideas are welcome.

Regards

Iyer

[Al_The_Man]

Possibly the rotor has become de-magnetized? Is the commutation on the encoders also?
Al.

[iyerks]

Dear Al

What would cause this to happen ?

And how do I verify that the rotor is demagnetized ?

Regards

Iyer

[Al_The_Man]

Originally Posted by iyerks What would cause this to happen ? And how do I verify that the rotor is demagnetized ?

It can happen by over current on the motor or even mechanical shock.
To verify it, you could rotate the armature externally and scope the three phase output, and if possible, compare it to a good motor.
Al.

[JRSS1996]

Two ways to test the permanent magnet rotor, I am thinking you said this was an AC motor. One is to hook a drill to the shaft, duct tape even works, and counter generate voltage through it and look and the three phase electrical signals with a scope. A week or broken magnet will look all chopped up and a good strong magnet will look clean and almost smooth. Check the RPM of the motor and the voltage, i.e. 2000 RPM and 150 volts. Now if you have a tach and can measure the speed that you are turning the shaft you can tell if you are generating the correct BEMF, as per the example at 1000 RPM back driven, counter generated you should be around 70-75 Volts, +- 10%.

Another way to check is by using a torque wench attached to the shaft end. The nameplate should provide stall torque and stall amp, if you apply have the stall amps via a dc power supply to two legs of the motor you should have half the stall torque, if not the magnets have a problem.