PM generator and 208 volt 3 phase

[Nick Name]

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.

[Ronmar]

Well that would work, been running that way for years on several sites I maintain that have 3 phase available for the old radar drive motors, so the sites are all wired that way as are the backup generator sets.  But unless you need 3 phase for something specifically, the added unused wiring as well as efficiency losses don't make much sense to me...

[Nick Name]

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

[mobile_bob]

i don't believe you will see any efficiency gains with a 3 phase head if it is connected on a single phase, and likely no real gains if connected for 208vac, you need to be using all 3 phases to get the benefits

bob g

[Nick Name]

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]

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

IF you are only using two legs off of the 3 possible phases, then yes, there are efficiency losses

[Nick Name]

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