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 Post subject: Junk-style isolation transformer
PostPosted: Sep Wed 27, 2017 4:22 am 

Joined: Mar Sun 14, 2010 2:51 am
Posts: 134
Location: Newport, Oregon, 97365 U.S.A.
I got this parted out ss audio chassis with a nice toroidal power transformer. The output was 46 volts, nothing I could use, but I noticed the transformer offered 100, 120, or 230 volt options by way of a terminal board. 6 wires from the transformer; that's right,
I figured: 2 starts 2 finishes and 2 taps. It kind of threw me tracing out the circuit tho: the way this one works is one winding has
no tap, and is used 100/ 120 as-is. The second winding DOES have a tap for 100 volts. I found that putting the mains 123 volts
to the untapped winding, and using the start and tap of the second transformer, I got 106 volts out, which is fine for me, for some
of the much older radios I have - close enough to 110. Anyway just wanted to point out that modern power transformers that have two windings for 120/ 230 ( approx. ) volt operation can be used as cheapo isolation transformers; you don't have to toss them in the recycle bin.
The best scrounged isolation transformers I ever found were actually out of some TV/ monitor set, like used at schools; it had a about 200 watt perfect 1:1 isolation transformer, because it was built to a higher standard of safety than the usual home TV.
The only caution about such cheapo transformers with the dual primary is, since you're using 1/2 the primary current carrying capacity, the power level you can use the thing for is about 1/2 of its normal operation. I have scrounged a number of such
transformers for isolation transformer use when the secondary voltage was of no interest to me.

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