120/240v xformer

[RJ]

Picked up a 2500VA isolation transformer on freecycle that I was hoping I could use to convert 120v to 240v split phase. I have a 2800w/3100w inverter generator that I would like to use it with.

Legrand

Pri 230/400v
Sec 115v
Sec 230v

50/60 HZ

Will this work?

[Tom Reed]

It needs jumpers to set the secondary output. s1 to s2 and e1 to e2 for 115v.

[RJ]

Pretty sure the silver terminal "blocks" on the left set are jumpers. I neglected to mention that.

It's currently jumpered as you mentioned,  I can input 120 E1 and S2 and get 240 out, however all I have are two hot legs of 240. I ideally need a neutral as well. The ground is isolated from the chassis so nothing there.

Thanks.

[BruceM]

It seems the primary windings are for 230/400V, so you are attempting to drive the secondaries to use it as a step up transformer.  This works, though with less efficiency and with lower output voltages, since the windings were designed to boost ouput voltages to compensate for losses and will now be dropping the output voltage instead of boosting it.

Alas while the diagram is poor, it would appear that you have no way to get the split phase output from the primaries. If the primaries were 120/240 (two sets of 120V windings which can be put in parallel or series) you could do this, though the voltages would be a big low on the output.  

So while you could use this transformer to create a split phase 115/230 output from a single pair of 230 or 400V input, you can't do what you want with it.

What you want is a single step up transformer with two sets of 115V output, or two straight 115-115 (or 120) isolation transformers with secondaries wired in series.

[RJ]

Bruce thanks for the reply. After doing some reading I decided you just use the Secondary windings on the transformer.


I jumpered E2/S1

I then input 120v into E1/E2 (hot to E1 and neutral to E2)

So now I get 120 V between E1/E2/S1 as you can imagine and I also get 120V across S2/S1/E2 and now 240v across E1/S2

I have left the Primary alone although I also get 240v without the neutral over there as well that is isolated.

Do you see any issues with this setup?

[BruceM]

RJ- Interesting use of the secondaries as an auto-transformer; I missed that possibility.  Voltage will not be perfectly balanced under load; s2/s1/e2 output may be a bit lower than e1/e2/s1 but you do get what you were looking for; split phase 240V.  Bravo.