Micro CoGen.

I wonder if the pm generator set to give 3 phase will run cooler than if set to give single phase?

Agreed, Bob. Of course one can use all 3 phases of a 208 volt set-up whether they are used on a 3 phase thing or not.  I have to think that because industry uses 3 phase almost exclusively (I once salvaged an industrial time clock that was 3 phase), it must be better.  3 phase motors are, by all accounts, certainly better, and when a well pump goes out, a 3 phase replacement is the smarter choice.

Ronmar, there are efficiency losses with 3 phase over 1 phase?

Since a PM generator apparently does not mind uneven power draw, why not use 208 volt three phase?  From one leg to ground you get 120 volts and across two legs you get 208 volts, which is just fine for 220 volt applications.  And then of course you have the three phase option, my personal favorite.  Also, according to the charts I've seen, three phase operation is about 6% more efficient than single phase.