[serialk11r]

Er, wait you can't turn the 3 phase summed power into DC if the rotor is switching? You would have to ditch at least one phase to get AC which you could then convert to DC by switching the polarity of the rotor.

Half wave rectification is an interesting idea; as you say it's not heat limited but winding resistance still limits power. Using half wave rectification on an oversized alternator for a car with low electrical demands could be a quick way to boost efficiency by a few percent. You could trim the cooling fan to reduce parasitic load further.

24V half wave rectification would keep power around the same, but raise efficiency at least at lower speed (iron losses will double). This actually seems DIYable, though a 12V alternator field coil running at 24V isn't great.