how do you hook up a balancing transformer

[Randybee1]

Ok guys, today's question is: I have an ST 7.5kw generator. Still building the system up but I'm looking into the future and the possibility I'll have unbalanced loads (it'll be wired for 240). So, what type of transformer do I need to balance the load? and how is it wired?

Thanks!

[Randybee1]

Additionally. Since I have a 7.5Kw head should I be looking for a 10Kw step up transformer?

[Tom Reed]

I'm using a generic transformer on my system and it works fairly well. Outback sells a dedicated balancing transformer that will do what you want. Look at their installation instructions for a schematic. That is how I did mine.

[Randybee1]

Tom, I looked up the Outback earlier today and saw the instructions. The Outback is very expensive. If all I need is a 10Kw step up transformer I can get them for significantly less but I'm not sure what size I need. Thanks for the info. Did you have issues before installing the transformer?

[glort]

OK, I'll admit my ignorance. I looked this up and still not sure what it's for.
Am I to take it that it shares the load across the 3 phases so if you have a single phase 1 Kw and a 2 Kw load it applies equal draw across all 3 phases?

[Tom Reed]

Glort, not necessary there. Here we use them to balance the load on our split phase system.

Randybee1, You are talking 2 different things here do you want to balance the load or raise the voltage? For load balancing there would be a max difference 3.75kw so a 3kw transformer would handle 99.9% of the situations. Yes my st5 would have one leg go low 104v and the other high 130v when the 120v well pump ran. The legs stay within 5v of each other now. To small of a transformer will just limit how much balancing it will do.

[mike90045]

The outback transformer can do both, or either.  Step Up or Balancing
http://www.outbackpower.com/downloads/documents/Hardware_Accessories/autotransformer/manual.pdf
but it's not 10Kw.
If you look for a 10Kw 120-240 step up/down transformer on ebay, you can get them pretty cheap.

[Randybee1]

For load balancing there would be a max difference 3.75kw so a 3kw transformer would handle 99.9% of the situations. Yes my st5 would have one leg go low 104v and the other high 130v when the 120v well pump ran. The legs stay within 5v of each other now. To small of a transformer will just limit how much balancing it will do.

Tom, So you are saying that since each leg will see about 3.75kw I only need a 3kw-ish transformer?. This is where I am confused. I thought if I was pulling a total of 7.5kw I would need at least a 7.5kw step-up transformer to balance my loads.

[mike90045]

It depends somewhat how you use the transformer. 
7.5kw genhead, I assume you are producing split phase 240Vac (120V per side)  which can get by with a smaller transformer
If producing 120V and need to upconvert and balance, the single 120V winding side has to carry the full 7.5kw
  So I just gave the manual, cause I find it hard to wire stuff remotely 

[Randybee1]

Makes a lot more sense now. Each leg will carry 3.75 kw so I size the transformer to approximately 3.75 kw, give or take a few watts.