Can a 240V/240V isolation transformer be used with 120V/120V?

[cdwitmer]

I have gathering dust at my house an APC Matrix-UPS 5000, a 4.7kVA UPS that puts out very clean sine wave AC in normal operation. (When inverting from batteries to AC, the wave form is nothing to write home about: okay for computers but not what you would want to use for audio.)

This UPS has a cut core transformer inside that must weigh close to 130 lbs. It is designed for 200/208/240V input, and it can output those voltages as well as 100/120V.

Since I have no use for the UPS (my house in Tokyo is not wired for 200V), I have been toying with the idea of removing this monster trannie from the UPS and using it as an isolation transformer. In my case, that would mean I would be inputting 100V to the primary side rather than the 200V that the transformer was originally designed to work with.

My thinking is, if you can get out 200VAC from the secondary side by applying 200VAC to the primary side, those same windings should yield 100VAC when 100VAC is input.

Is that line of thinking correct? Or am I missing something? As a newbie I am reconciled to the fact that many of my imaginings are just that, vain imaginings. I see lots of transformers listed as 240/240, and others as 120/120, and of course some 240/120, but I don't think I have ever seen a transformer where the manufacturer claimed that the same sets of windings would be equally suitable for either 240/240 OR 120/120 applications. Yet it seems to my "newbie mind" that a 240/240 transformer should also work as a 120/120 transformer simply by halving the input . . .

Any insights in this dept. would be greatly appreciated!

Thanks,

Christopher Witmer
Tokyo

[ThomasW]

I briefly talked to Jon about this....It appears once again the answer is no, because the trannys used in most UPS's aren't like those used for normal line voltages given the nature of how a UPS operates.

Tomorrow he'll drop in and post a follow-up if necessary.

Might be best to bite the bullet and import one of the "Q" transformers-in-a-box from Equi=tech. That will give you what you want, but of course at a price....

[cdwitmer]

I had to give up on Equi-Tech: 50Hz models co$t more

Thanks, Thomas.

I would jump on the Equi-Tech trannies except the affordable ones are 60Hz models and will (apparently) not perform well with 50Hz . . . and would probably have both acoustic noise problems and a tendency to overheat.

Equi-Tech can of course make me a transformer that would be perfect for 100V/50Hz, but the price is way out of my range: several times what their oversized "blem" units go for.

Plitron's "Secrets" 2kVA transformer is also a 60Hz transformer, and I am still waiting for a reply on what they would charge me for a 50Hz version. If it is reasonable I may go with that.

Thankfully, I can always fall back on Avel-Lindberg Y23 series transformers, which are rated for 50/60Hz (this may account for why they are surprisingly silent in 60Hz operation: they are probably slightly oversize for 60Hz). Parts Express can special order 1000VA units from Avel-Lindberg for $79 each. If I go with Avel-Lindberg I'll have to get three transformers, which may not be entirely bad since I will probably have an easier time with inrush current in 1000VA transformers as opposed to 1500VA or 2000VA units.

[ThomasW]

According to Jon he thinks you can run one of the stock Equi=tech "Q" 'transformer-in-a-box' units. They're so overbuild that the only downside is that they might run slightly warmer at 50Hz, so de-rate them down from the normal 15 amps.