1:1 electronics testing and servicing isolation transformer - ON THE CHEAP DIY

A 1:1 isolation transformer is a safety must for floating an open chassis piece of equipment that you have under test while using an oscilloscope.

1:1 isolation transformers are expensive so what's the alternative????? build your own DIY version, so please throw in your experiences for a cheap work around to the problem.

http://www.youtube.com/watch?v=xaELqAo4kkQ

My findings so far;

1. modify MOT (microwave oven) transformers. (use two identical units cut them open with an angle grinder and rebuild one of them using the two primary's, spot welding back together or bolting them back together at the disadvantage of destroying/damaging the core.

http://www.youtube.com/watch?v=iru58TO14x4

2. Still using the two MOT transformers but this time leaving the primaries in tack but cutting the 2000v secondary's away, rewiring  with fresh wire and joining them using two transformers to get your 1:1 ratio.

http://www.youtube.com/watch?v=QDSmv9E5VgQ
http://www.raphnet.net/electronique/isolation/isolation_en.php

QUESTION.....What would you wind in the middle of the two,,,,size of wire/number of turns?

3. Using a common 12v car to mains invertor to run your oscilloscope off. (its a pain dragging car battery's round and acid in my lab/house is not desirable)

4. if you have a small generator at hand using that.....(sadly I don't have this option).

So Guys using MOT transformers are ready available that people chuck out and are cheap but the disadvantage is cracking them open destroys the core, so does anybody have experience of joining two of them together? What did you do?

Oh bye the way I'm in the UK on 240v

if you are going for a not hi quality one you can go with some variants... the two transformers as you said but not touching them, just connect both 240V toghether and use each 2kv as pri and sec... the other is to get a core, some wire and star to wind... thin wire and a lot of turns will work just fine, probably not good without calcs but you dont have much to calc if you don't know where it will be placed. if you don't need too much isolation bifilar wound will be the best.

you could also get a cheap 1:1 iron but all this options are not so good quality and i don't know if you are looking for something special or just protect your osciloscope in initial audio tests till see whats happening and then go direct when you know there isn't anything so wrong.

JS

I have tons of ex UPS transfromers varying from 250VA to 1500VA.  These have 230V in and 12V out. Pay the shipping and I'll send you a pair with my compliments. However, I am on hoilday at the moment and I will return to UK on 7th August. If ok then PM me to remind.

Sounds Great