isolating transformer

Discussion in 'The Projects Forum' started by juggler73, Oct 26, 2010.

  1. juggler73

    Thread Starter Member

    Apr 10, 2010
    im looking to build a Mains Isolating Transformer for safety when working a lcd monitor's power supplies
    ive seen that i could use 2 transformers of the same rating but not sure on which what type
    can i use 2x 240v - 12v 50va and connected then up or do i need some more powerful
    any help with this matter would be great
  2. kubeek


    Sep 20, 2005
    You need as many watts as your most demanding lcd needs. For lcd monitors 100W should be enough, but for large screens even 300W could be too small.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    You do not want to use a step up or step down transformer. You want a 1:1 isolation transformer that gives out the same voltage it takes in. No step up or down.

    Use the "1:1", or One to One term in the google search for a transformer and you'll get lots of info.
  4. kubeek


    Sep 20, 2005
    Stepping down and up again is not a great solution, but if you have the two transformers with same voltage and high enough power rating it is better than nothing as obtaining an isolation transformer can be hard in some places.
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    And MUCH cheaper. 1:1 isolation transformers run in the 3 digit price range. A couple of 120-12V transformers with a high enough current rating will step the voltage down, and back up, giving isolation. Complete with box, it is still under $50. Remember to add fuses and breakers to the system as well.

    That said, a 1:1 is PREFERRED, as going over about 300 watts with the step-down, step-up is a bit difficult.
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    Unless U want to use scope on an LCD supply, u do not need Isolation.

    Cause the way I see it, Isolated or NOT, SMPS primary deals with high Voltage.
    If u scared to probe that area, a transformer is of no help.
  7. debe

    AAC Fanatic!

    Sep 21, 2010
    Here in Australia quite a few old TVs had 240v to 240v isolation transformers varying from 100w to 200w I have used one of these mounted in a suitable box for working on live chassis, cheap way of doing it & works. Daryl
  8. someonesdad

    Senior Member

    Jul 7, 2009
    You can also look for used equipment. New isolation transformers are expensive, but I found a 1 kW medical grade isolation transformer on ebay for $60 delivered a few years ago. Most of that was probably shipping expense, as it's pretty heavy.

    As others have said, hooking two identical transformers together is a perfectly acceptable solution as long as you respect the power specs.