1:1 Line Transformers

Discussion in 'General Electronics Chat' started by lollupaandi, Sep 7, 2012.

  1. lollupaandi

    Thread Starter New Member

    Sep 7, 2012
    I'm trying to buy an 1:1 isolation transformer. My application is very similar to this -


    I'm looking to draw not more than 0.75 A on the secondary.

    In the thread above, people talk about isolation transformers not being that expensive, but I'm unable to find anything reasonably cheap. I searched on DigiKey and Mouser, but could not find anything.

    Could you guys point me in the right direction?

  2. MrChips


    Oct 2, 2009
  3. absf

    Senior Member

    Dec 29, 2010
    I have a 230V:230V 50Hz isolation transformer that was rated at 250W and it is big and heavy. I used it mainly for repairing TV sets and SMPS PSU for safty reasons.

    During the 80s, all the TV sets sold here were hot chasis and it was quite dangerous repairing them without an isolation transformer.

    For designing SMPS, you only need it during the design phase. After that it can be removed and your SMPS plugged directly onto the mains.

    I also have a 230V:110V isolation transformer that came from a dismantled telephone Exchange built in a 40-feet container. It was mainly for Japanese test gears and wire wrapping guns using 110V. I got my Apple IIc and and its monochrome monitor from US eBay and it was working on that transformer.

    Last edited: Sep 7, 2012
    lollupaandi likes this.
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    If you have two regular transformers of the same value you can make a isolation transformer. The transformers need to be the same though. Get two transformers that have the correct VA rating you need and wire the secondaries together, and you then have a isolation transformer.

    An example would be two 110V:12V transformers, it wold work like this -

    110V primary -12V secondary - 12V secondary - 110V primary. 110V in 110V out.
    PackratKing and lollupaandi like this.
  5. lollupaandi

    Thread Starter New Member

    Sep 7, 2012
    Thanks all, that was helpful.
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011

    But what's a VA rating? Literally volts time amps, or how much power can the transformer handle.

    It's not always listed, it's in the full spec sheet but you may just know the secondary voltage and current. That's fine, multiply them, divide by the line voltage, and that is the current this combination can safely handle.

    Example: a 12VAC secondary rated for 7.5 amps.

    12VAC * 7.5A / 120VAC = .75A