# Question about LEI Power Transformer

Discussion in 'General Electronics Chat' started by Pappy, Dec 26, 2010.

1. ### Pappy Thread Starter New Member

Dec 26, 2010
3
0
Hi everybody,

I was able to salvage a power transformer from a APC 1000 watt UPS unit and being trying to find more info on this baby but nothing on Internet.
I have included a picture so you can get a better feel for it.

Right now i am using the primary White and Black wire and i guess i can make a linear 13.8Vdc 20~40Amp power supply with it.

Its a 430-1217A Rev.3
LEI-4 E154515.

This thing weight is 16 pound 5 ounce. It would make an anchor for sure.

The primary consist of 4 wires, White-Black-Yellow-Blue (12 Gauge) in that order.

The secondary are Black-White (10 Gauge).

Here are some value i have taken between the following wires on the primary.

White-Black..= .29 Ohm with a 15.75 Vac on secondary.
White-Yellow.= .30 Ohm with a 13.75 Vac on secondary.
White-Blue....= .34 Ohm with a 12.10 Vac on secondary.

The following combination will pop a circuit breaker for sure.

Black-Yellow = .087 Ohm
Black-Blue = .13 Ohm
Yellow-Blue = .08 Ohm

Pappy

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2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
290
This is a funny animal. For a 1KW output, the input (assuming 12 volt batteries) would have to be driven at over 83 amps. By the same token, the output is only 8 and a fraction amps.

The wire gauges do not work out. If we assume the secondary is the 120 VAC output, then 10 ga is ridiculous. In the same way, the primary pairs with 12 ga wires can't possibly handle the current - unless the battery voltage is way above 12.

I found some stuff online - http://www.diyaudio.com/forums/power-supplies/67232-stupid-question-but-looked-like-place-ask.html

Worse come to worst, the salvge value of all that copper should be pretty good.

3. ### Kermit2 AAC Fanatic!

Feb 5, 2010
4,165
1,120
Switch mode power supplies, have unique transformers. Nothing that would substitute for the transformers found in your standard, linear type, power supply will be found in one of those supplies, except in rare circumstances.

4. ### SgtWookie Expert

Jul 17, 2007
22,194
1,761
I have a couple of 1kva APC UPS that are designed for rack mounting. They use four 12v 7AH SLA batteries, wired in series-parallel; so the primary side of the transformer was receiving in the range of about 23v-28v when acting as the supply. I haven't bothered reverse-engineering them.

5. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
202
If we think about a UPS it only supplies a small amount of charging current to the GelCell batteries but an enormous amount of power going the other way. I've got a 1,200 APC in my room and it does use two 12V 12 AH batteries in series so at 100% efficiency you'd need 24V at 50A for the full output, but also remember these are rated as VA which ends up sounding like a lot more output than they can actually put out in true RMS watts. They also don't have the longest run times in the world, if I ever had to hit mine with full load I doubt I'd get much more than 10 minutes out of it.

No way can you go on the simple DC resistance readings, what you really needed to do was to reverse engineer the circuit as you salvaged the transformer, that or see if you can get a schematic out of APC or somewhere on the internet.

If you ever get the chance add a variac to your test bench but mount it in a case and remember that they aren't isolated so you've got live mains regardless of the setting. Isolation transformers aren't too hard to find but it's often far cheaper to make one by finding a couple of surplus 480:120V control transformers of a decent wattage and hooking them up back to back such that you've got 120 in and 120 out. If you're lucky you can grab a couple of 500W, 750W or even 1KW ones for about \$10 each at a local surplus house that deals in taking apart older industrial equipment and reselling it. On occasion you'll find them on eBay but the shipping alone can kill unless they're willing to use a flat rate USPS box.

When you've got a variac you can deduce a lot of things about an unknown transformer.

Jul 26, 2010
2,358
202
7. ### Pappy Thread Starter New Member

Dec 26, 2010
3
0
Hi Guys,

Thanks for putting me on the right track. It was stupid of me to think it was an ordinary transfo.

First of all, i should'nt have use the word Primary and Secondary as such. I assumed that the heavy wires where the secondary low voltage hi current but in a UPS configuration its probably the reverse.

Basically, i wanted to build a 13.8Vdc 20-40 Amp power supply...?
I guess i will do more searching on the subject.

Thanks again for the 3 links, especially the third one...

8. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
202
Complicated schematics but at least you can see how they're doing things. Sideways schematics always bothered me though so printing them out might prove to make them more readable.

Of course you can always use <CTRL> + <ALT> + an arrow key to rotate your display in Windows. Hit that combination by accident once and it was heck trying to look up what had happened and how to get it back to normal. Now that I know it I use it on occasion.

Pappy likes this.
9. ### Pappy Thread Starter New Member

Dec 26, 2010
3
0
Marshallf3,

Yes its a bit complicated but its better then nothing.