Suggestion to macgen1 (Electrical) Jul 30, 2003 marked ///\\Addn info/Correction to original question. The motor has been operating for approx 4-5 years at 1538 rpm without falling apart, so it would seem that mechanically at least the increased speed of operation is within the motor design margin.
We have seen significant brush wear out (split brushes) and pitting damage on the comm. While part of the wear out of the brushes would be due to increased speed, we are also on occasion seeing incredibly rapid wear out (<300hrs operationas well as arcing from the brushes to the holders and melt down of the holders. To date no-one has been able to determine why this is occurring.
I have a few theories that maybe the 25% overspeed of the motor is
- altering the neutral plane,
///Yes, somewhat, since the counterelectromotive force will be higher.\\ or
- reducing switching time when the brush changes segments, resulting in higher emf at the brushes,
///Yes; however, the magnetic energy stored in the winding and being switched tends to have a shorter time available to change with the reduced switching time.\\ or
- causing circulating current around the split brush system,
but it's a long time since Uni and we have noone with experience of DC motors within the company who can advise.
///Please, would you elaborate on this one.\\ Most texts I've found do not consider motor overspeed situations.
///When it comes to DC motors with series winding, the overspeed situations are addressed.\\Would really appreciate anyone who can confirm or eliminate any of these theories. The manufacturer tech support has only been able to say that they don't know what would happen at this speed as they only tested to overspeed of 1370rpm.
///Try a different manufacturer tech support. Some tech supports "play things safe."\\ Thanks.