The Wind is Free!

Where does the 4th wire go on the 3 phase stator?

Nowhere, if I understand your question. Three come out to the rectifiers, and three are just connected to each other.

I only ment to ask as I see 4 wires as a rule in all 3 ph insallations.

Perhaps you mean on mains supply? There you have one for each phase, plus an earth wire.

On a stator, there are three phases, each with two ends, hence six wires.

I get the fact that while I use one bank the other charges, what would I use to control the switch over from the one to the other?