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Unread 16-06-2003, 17:40
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Quote:
We are burning out motors (we've burnt out about 10 so far) and have tried everything we can think of to keep them from burning out. They burn out (we have verified the brushes get fried or broken off) seemingly at random -- not necessarily due to excessive use -- and the motors often are not even that warm when we touch them after they malfunction. We have changed our control algorithms to reduce the maximum duty cycle to less than 40%, and even that does not stop them from burning out.
It could be that the brushes on this motor are crap. Some motor's brushes are very fragile. The drill motors are one of these motors that come in mind. One thing which may do it is to support the brushes. Btw what motors are you using?? I may be able to hook you up with something that may be a good alternative.

Quote:
Our electrical engineers are hesitant to switch to 4000 hZ because they say performance drops as the PWM frequency increases
According to my book PWM frequency is an finicky thing to answer. Higher frequency is less likely to cause a mechanical vibration in the motor. Lower frequencies may cause your motors to vibrate or whine.

Here is an equation for determining PWM frequency:
2(pi)(f)(L) is much greater than R
where f is switching frequency
L is armature inductance
R is armature resistance
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Last edited by Adam Y. : 16-06-2003 at 17:49.
 


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