Isolation transformer?

You can use a 120/240-to-anything transformer as a 120-120 isolation tranny. Connect one half of the official primary to the line and use the other half as the isolated output. Ignore the "secondary". The power rating will be a bit less than specified because you're not using all the copper.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

it depends how much isolation you need, using two secondaries, or two primaries as halves of an isolation transformer only gets you functional insulation, not any kind of safety isolation.

if the output is grounded and the input is fused, that may be enough.

--
  When I tried casting out nines I made a hash of it.

You can, that is the intent on providing the duel windings.

** A 120-120 transformer does not have equal windings, the secondary has additional turns to allow for the regulation factor of the unit. Might be anywhere from 4 to 20% extra turns on the output side. Also, a properly made 120-120 would also have good insulation between the two windings rather than them being overlaid or wound bifilar.

Another factor is magnetising current - transformer primaries are sized to allow for the extra current but secondaries are not since there is none.

** Yep - the VA rating describes what rms current x voltage available from the secondary.

.... Phil

** I guess those "duel" winding get to really fight it out ?

... Phil

** The secondary voltage available under load will be lower than the input - depending on the regulation of the particular unit. ** Actually it will be higher for the same reason. With rated current in both halves of the primary, having no secondary current means the unit will run cooler - allowing up to 41% increase in primary current.

AC supply transformers are tricky things.

... Phil

You are right, I screwed up, and it wasn't so you could show how petty and insecure you really are.

** No sense of humour = typical ASD f***ed troll.

.... Phil

I have one you can have for free. You just have to pay postage.

It weighs in at 9 lbs.

Bando Shielded Power Transformer Yamaha BD21A35E-0004

I forgot this.

This came from a Yamaha 240 watt receiver.

Thanks, but my need for one has gone away.

...

Thanks - I had overlooked that. It might not have mattered (lower output might have been OK), but I'm not going to use one now.

Thanks for the replies; I've decided not to use a transformer.

s additional turns to allow for the regulation factor of the unit. Might be anywhere from 4 to 20% extra turns on the output side.

he two windings rather than them being overlaid or wound bifilar.

to allow for the extra current but secondaries are not since there is none .

** Funny how we get the same question here regularly - and the same answers .

facts.

He has commented, more than once, that he treats usenet posting as a big j oke.

What he doe not realise is how that makes him look like a big joke.

.... Phil

If you think your rudeness is somehow humorous, you don't know the definition of humor. But perhaps you'd like to double-down, dig yourself in deeper and explain...

Sort of. Vout will be a little low under load due to copper resistance. Tha t could be solved by putting eg a 12v secondary in series with the output, connected right way round. But the big issue is that you won't have a level of isolation that's considered safe for many applications. For some jobs i t's adequate, for many not.

NT

Not mine. It is built from a very high power amp, around 1,000 watts per channel. The secondary at 120 puts out 127, when I load the shit out of it and it drops to 120 the line voltage drops to like 116.

I had to scrap it, the amp boards got soaked with the elements and got conductive, and the protection didn't even work and it had offset and was blowing speakers.

It came out of a bar in the ceiling and I think the roof leaked on it but they didn't own the brick and mortar so they didn't give a shit.

Anyway, the load that made it drop you 120, a 1,500 watt electric heater. I don't even want to think what one with that capacity would cost. I go it for free. I didn't charge any fee just kept it, which they were cool with.