- Joined Oct 3, 2010
I have a 15hp 3phase motor that was making wierd groaning/vibrating noises. The oscillating noise was consistent, but not consistent with the rotation of the motor, i.e. it wasn't every revolution that the noise happened, but rather maybe every 10th revolution and lasted maybe 10 revolutions (pure guess as to the revs, I didn't put a tach on it, it's only an example). I am not the one who troubleshot it; a guy on another shift troubleshot it. He disconnected the motor from the load and ran it, and said it still made the same noise. He therefore diagnosed that the motor was bad and a new one is coming. I was told to take the motor out, which I did, and afterwards I wrapped a cord around the shaft and pulled it like a pull-start lawnmower. That got it up to maybe 100-200rpm and I could not hear any noise coming from it at all, and it was smooth as butter. My supervisor (a mechanic) said that one time he saw the same thing, and it turned out to be the drive and not the motor. I was wondering, has anybody seen a drive do this before? I have seen some BLDC controllers that can send specific frequencies to motors an make them play a little tune, and you can hear the frequency of an industrial drive while it's running, so I guess its plausible that if something went wrong in the VFD, it could produce an audible noise in the motor. thoughts? experiences?