Isolation transformer question

[Koolaide]

Isolation transformer.jpg

Hi all,
I'm back with more questions retarding Isolation transformer.
I purchased an Isolation transformer off the bay. reported to be 1200 watt 120v primary and secondary.
The transformer is large, and has 2 sets of leads, one red and one black. The unit is Precisions Electronics NECO 11.(I couldn't find anything on the net regarding specs ect..see photo attached
I am trying to determine primary and secondary. I am assuming the black is primary and the red is secondary. There is continuity for each pair with very low resistance that is almost identical. (,003/.004) No continuity for primary and secondary. I would assume the secondary would have a few more turns to account for loss, but am only guessing. My next step is to connect to a variac and run about 10v to see if I can see a difference in turns.
Does anyone have any experience with this IT?
Are my assumptions above correct?
Any recommendations regarding testing or other thoughts?
Thinking in terms of ohms law, I was sorta expecting to see about 12ohms. I am sure this is a gap in my knowledge. Any enlightenment would be appreciated.

Thanks again,
Jim

[Phil_S]

I'm not sure it matters. An isotrans is 1:1. If you feel you must verify, a simple first step is to check the DCR on each winding, which you did. If DCR is the same, wire gauge is the same, and Vin = Vout, how could the number of turns be different?

If you have doubts about the accuracy of DCR, you might put a very small value resistor in series with the winding to shift the reading into a better range for your meter.

[Koolaide]

Thanks Phil.
I was under the impression that the turns on the output could be a few more to account for loss. I could be wrong, hence the question. The DCR is minimal on both sides as noted above. I was thinking the difference in turns would be so minor that is might not show In DCR. Thanks for the reply.

[pompeiisneaks]

a simple way to test, is if you have a variac, set it to something simple like 10VAC and connect the output to one side. See what you get on the other. Should also be 10VAC as well, and you're in a voltage range that's pretty safe to not hurt yourself.

Agreed, though, that it should just be 1:1.

~Phil

[Phil_S]

No variac needed. 120VAC should be no problem for your meter. Rig a fuse and a plug on the wall socket side. Screw the secondaries down so they aren't flying in the air. I'm doubtful about any loss at a fraction of 1Ω. Remember to measure VAC on both sides. The wall supply won't be exactly 120. Follow good safe practices when doing this!

[pompeiisneaks]

No variac needed. 120VAC should be no problem for your meter. Rig a fuse and a plug on the wall socket side. Screw the secondaries down so they aren't flying in the air. I'm doubtful about any loss at a fraction of 1Ω. Remember to measure VAC on both sides. The wall supply won't be exactly 120. Follow good safe practices when doing this!

It's more about not electrocuting yourself on accident.

:O

~Phil

[Phil_S]

It's more about not electrocuting yourself on accident.
:O
~Phil

Stop licking your fingers, Phil!
Seriously, the right way to do this without a variac is to somehow breadboard it. This can be as simple as screwing everything down to a plank of wood. No floating wire, no loose transformer. Screws make decent test points.
Better than screws, I like this type of terminal block:
https://www.alliedelec.com/product/weco ... lsrc=aw.ds

[DimenBrun]

If you're worried and you don't have a VARIAC, then a small wallwart (that outputs AC) can be used. Most of these are DC(rectifier, filter cap) but there are some that are AC(just a stepdown xfmr). Something 6 - 12VAC would be fine and you could then verify 1:1 turns ratio using the low voltage AC output from the wallwart.

[Koolaide]

I am fortunate and do have a variac.

[Phil_S]

I am fortunate and do have a variac.

That still doesn't mean it's OK to lick your fingers
Let us know what you find out. I'd like to know. Thanks.

[Koolaide]

Finally had a chance to test the IT 129v in 131v out. Looks like is all good. Now time to build an enclosure.

And just for Phil_S I didn't lick my fingers … this time


Thanks guys for all the answers. I'm a rookie, so more questions to come.

Jim

[Phil_S]

That's with no load. the 1.5% difference will probably disappear in use. There could be additional loss. It probably depends on current rating.

[Koolaide]

I kind of figured that Phil. It's pretty massive. Sold as 1200 watt. By my elementary school math and Ohm's law I come up with 10 amps@120v. Given the low Ohms across the windings .003/.004 Ohms, I am guessing I should be OK, as I don't envision using it on anything over 4 amp mains.
Let me know if I'm missing something.
Thanks,
Jim

[Phil_S]

Yeah, I'd say 1200W/120V = 10A. Sounds good to me. But I don't know much.