how do i center tap a 15kw st gen head

[cohippy]

hello everyone this is prolly a stupid question, but how do i cener tap a st gen head for 240v and 120v at the same time? i cant seem to find the answer to this question anywhere or im just not "getting it". reason i ask is is there is no way i can afford a 20kva transformer to run the gen head at 240v to be sure to evenly distribute power over both coils, no im back at what i did not want to do, anyways thanks

[akghound]

I am surprised no body has chimed in.
Wires marked U3&U4 tie together for neutral (center tap) this leaves U1&U2 as hot. You will have 220 vac between U1&U2. There will be 120vac between the U3/U4 junction and U1 or U2. Make certain your neutral connections are secure. If the neutral should somehow become disconnected there will be 220 across the two 120 legs, this equals lots of smoke and a trip to the dump with burned up appliances. 
One could run separate neutrals for each leg of 110, they would both tie in at the U2&U3 junction.
Hope this helps
Ken Gardner

[akghound]

Found these diagrams



There should be a Jumper between U3&U4 in this Diagram. Center Tap/Neutral

on this page
http://www.utterpower.com/installa.htm
Ken Gardner

[Ronmar]

Ken, I think you missed or mis-typed a "U" in that first explanation.  I think there should be 4 "U"s.  As far as I understand ST wiring, U1 and U2 are the far ends of the two main stator windings.  U3 and U4 are the middle ends.  You may also have a U5 and U6 if the generator was also capable of running at 50HZ.  U3 and U4 are tied together.  This is also the connection point for your neutral wire. This point will also be tied to ground in your electrical panels.  As mentioned, it is VERY important that this connection is done properly so as not to fail as ken mentioned.

As for the generator output, think of it like putting two batteries in series.  U1 to U2 = 240VAC and are often refered to as your "hot" wires.  Either U1 or U2 measured to the U3-U4 junction will = 120VAC.  

U5 and U6 are simply extensions of the main windings to give rated voltage output when the generator is spun at the lower 50HZ/1500 RPM.  For 60HZ you don't mess with them and leave them disconnected...

U1                 U3--------U4                   U2
\                 /                  \                 /
 UUUUUUUUU-UUU         UUU-UUUUUUUUU
                       \        /
                       U5    U6 For 50HZ only

Utterpower.com has some good St wiring info, as does Georges CD... 

Looks like we typed these up about the same time:)

[akghound]

Yes I did make a mistake in the "U" numbers in my first post. 
Good catch and thanks.
I went back and corrected it, at least I think it is correct now.
Ken Gardner

[Ronmar]

Where you talk about running separate neutrals at the end, the neutrals should connect to the U3-U4 junction.  There should be no U2-U3 junction:)