Quote:
Originally Posted by Daox
Ok, so the controller shuts off its PWM, then you get voltage spike (I'm a little familiar with this due to some reading on switching mode power supplies) which is increasing the current to get rid of the stored inductance of the motor? So this means that even though the PWM pulse is over with, you're actually still getting some motive power (for a very very short time)?
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Yep,
Because the motor is a huge inductor once current starts to flow it wants to continue to flow even after the battery is disconnected.
This is why PWM even works at all, if there were no inductance you would get effectively a short circuit and blow up (inductance opposes current flow and opposes current shut off as the field slowly callapses)
Also because every motor has a different amount of inductance it means that a PWM percentage does not directly coorelate to a voltage.
In the case of my little 48v motor 50% PWM on roughly 52v gives me about 36 volts give or take, not the expected 26v, obviously there are a few other things going on with my meter but a motor is an analog device with a curve much like a gasoline engine so each one is unique and behaves differently when exposed to a given voltage and PWM percentage.
PWM speed also affects this, since the decay time is different on slow switching speeds (which also increase friction/resistance losses)