Motors as Generators

We already know that a DC motor fan with permanent magnet and coil will rotate if we put electricity to the coil, at the other side, coil produces electricity when the rotor is rotated. My question : If we connect a battery to a motor, then we assume that battery drive the motor, right? And it rotates the motor at a certain RPM. What happen if by using external power like air compressor we speed up the fan blade to rotate the motor at double or even more RPM? Will we find that the motor now is charging the battery? Or maybe we could find at what RPM that no drive and no charge but the fan still running? Thanks
- Lucky (age 47)
Indnesia

Yes, if you push the fan fast enough the net flow of energy will be back to the battery and it will charge up. I'm not sure how much faster that would have to be than the usual rotation rate, since some energy is lost to friction, Joule heating in the wires, etc.

Mike W.

(published on 07/20/2016)