Quote:
Originally Posted by Mxfrank
This is true in the case of a fan or blower, which have considerable momentum and can coast for some time. But when a window motor reaches the end of it's travel, it's stopped dead, so it can't become a generator. At that point, it becomes an inductive load which consumes electricity and produces heat. The heat will trigger a thermal switch which breaks power in case the switch isn't released. When the switch opens, stored energy in the motor winding is either dumped back into the harness as a reverse spike or released as heat.
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You are forgetting about a partial window movement where motor becoming a generator is relevent.
Think about the person that wants the now closed window open just a crack for air. Down , overshoot , up overshoot to fully closed, down . . . . Darn car. . .
A stalled brush type motor powered by DC is a restive load rather than an inductive load. It would be inductive only at initial power up / power off.
If this same stalled motor was powered by AC, there would be an inductive as well as a restive load. If this was a permanent magnet brush motor, the inductive load would go away once the " permanent " magnets became demagnetized. Winding failure might occur prior to this happening though.
At old job, we were stall testing 1 to 2 HP 90 VDC motors on 180 VDC. Every once in a while, the permanent magnets would flip polarity and motor would run in reverse.
From what I recall, some motors would run faster after a test due to field weakening but lose torque in the process.