Quote:
Originally Posted by redpoint5
The silly thing with motorcycles is they use generators and shunt excess power generation to a heat sink. I'd like to shut my generator off too. I wonder how much power it robs from the engine? Probably should have done that during track days.
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No, it uses PWM to short current through the stator to cancel out the rotor's magnetic field. That gives increasing copper losses as the rpms go up, but removes excess iron losses. The regulator itself is pretty efficient, and they could make it more efficient with bigger MOSFETs. If it used the regulator to burn off power that thing would go up in flames in seconds even if it had the biggest heatsink ever.
This control strategy is actually more efficient than an alternator up to a certain point, but the stator losses go up quadratically with speed due to the permanent magnet and start wrecking efficiency. I would guess that at the rev limit, a motorcycle generator is probably under 30% efficient vs. maybe 40% on a car alternator.
Since the stator is so undersized on a motorcycle, I think the highest efficiency option is to wire in a synchronous rectifier and DC-DC converter. I'm kinda curious how many motorcycles already have synchronous rectifiers, since you can use the same MOSFETs to do the PWM, so it would reduce the number of parts.
The actual best thing to do is to put in a bigger stator with lower winding resistance, but I'm guessing you'd need to do a lot of cutting to make that happen
