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transformer games

I have a 480 volt only transformer and DC power supply built a bit differently than any I've seen. There are six separate little wire coils, three primary and three secondary. No taps at all, one end of each coil goes to the outside world. The other end of each set of three is wired together to form a node, a sort of neutral.

Here's ASCII art for the primary: (the secondary is a mirror image)

L1-----Coil1------ | | L2-----Coil2------ | | L3-----Coil3------

OK, I don't have 480 three phase. My question, can I start re-wiring this to use 240 three phase or even single phase? I'd like to try wiring the primary coils: L1 to L2, L2 to L3, L1 to L3. I'd also like to try single phase: put all primary coils in series, all secondary coils in series.

Will this just blow fuses? Other issues?

OK, the voltage won't be exactly right. Can I remove a few turns to raise or lower the volts out?

Karl

Reply to
Karl Townsend
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You can't run this transformer from single phase without a serious loss in power rating. Two phases missing will also probably freak out whatever is attached to the secondary side, unless it was designed for this, which seems unlikely if it's using a transformer.

Tying the coils together in odd ways won't work either. If you rip out the primaries and rewind them with half the turns, you're good.

Yes, but a few turns won't help you in this case.

How large is this tranformer? It's probably not too hard to run it off another 3 phase autotranformer or something like that.

Reply to
Cydrome Leader

There's no need to rewire for delta, just leave it in the wye configuration. What is the voltage rating at input and output? Ie. if it is now a 480:240 transformer, it is also a 240:120 transformer, just as it is! If you connect 240 to the input, you would get 120 V 3-phase out. The KVA rating is half, as you've cut the voltage in half, but the amperage rating will still be the same.

If you want to trim the voltage, removing primary turns will raise the output voltage, adding turns in the same direction will lower the output voltage.

Jon

Reply to
Jon Elson

Maybe I wasn't clear. I need 280 to 325 V DC out after the diodes. So, going from about a 2:1 to just less than 1:1. Or put another way, 1/2 the voltage in, same voltage out.

Karl

Reply to
Karl Townsend

Wiring it in delta will give you effectively 277Vin/Same voltage out . If you apply 240 V you will get 240/277 time the original voltage out (assuming it is just a rectifier)

jk

Reply to
jk

If you want less DC output voltage, the easy way is not to bother with the transformer windings at all, but to replace the 'rectifier' parts with SCRs. And, an electronic controller to switch 'em in the proper phases to get to your target output voltage. The bonus, is that there'll be a knob that adjusts the voltage to anything you want, without any further rewiring.

Reply to
whit3rd

I haven't seen the specific transformer mentioned, but there is no hot/line source isolation with SCRs as a replacement-for-transformer method.

Reply to
Wild_Bill

No replacement of transformer was intended; the suggestion was to use adjustable timing of the triggering of SCRs instead of diodes on the isolated secondary of the transformer. The intent is to adjust downward the DC output. High power systems (welders?) frequently use this kind of scheme.

Reply to
whit3rd

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