Isolation for use on old TV chassis

[Electronics-Repairman]

Hi , I'm going to do some work on an old TV, so I want to build a mains isolation box, which I would use on just about anything with line power coming in any way. I have my mind tied up in knots with this , and hoping someone  can shed light on what I'm about to explain I'm thinking two transformers   the first one 240 primary and 50 secondary , the second one turned around  50volts/ 240 as output ,   so it would go 240- 50 - 50- 240 ,using the first as step down and the second as step up. hope this is making sense. And would this configuration work.

[rob77]

it's better to use a 240v/240v transformer - it's called isolation transformer.
but if you don't have one and you have 2 identical transformers with a sufficient power rating then you can even use the step down + step up.

[Electronics-Repairman]

it's better to use a 240v/240v transformer - it's called isolation transformer.
but if you don't have one and you have 2 identical transformers with a sufficient power rating then you can even use the step down + step up.

Hi Rob OK, this was the reason for asking I do have 2 transformers rated at 240/100v and 2x 240/50, so I'll use  one of the pairs probably the 240/100v pair.
Cheers

[kingofkya]

You can get medical surplus transformers pretty cheap all you need to do is remove the grounded strap to Neutral, and they are very nicely built inside.

I wish could be more help looks like there mostly available in the us. I have a dale/fluke 5amp one that I got for $50 delivered in the us.
http://www.ebay.co.uk/sch/i.html?_sacat=0&_from=R40&_nkw=isolation+medical+transformer&LH_PrefLoc=2&_arm=1&_armm=63&_ruu=http%3A%2F%2Fwww.ebay.co.uk%2Fsch%2Fi.html%3F_sacat%3D0%26_from%3DR40%26_nkw%3Disolation%2Bmedical%2Btransformer%26_arr%3D1

[bance]

A good inexpensive source in the UK would be builders 110V site transformers, they often have a 240-240 centre tapped transformer....

[Electronics-Repairman]

A good inexpensive source in the UK would be builders 110V site transformers, they often have a 240-240 centre tapped transformer....

Thanks Bance  I know where there is one, doing nothing, never even give them a thought.

[Monkeh]

A good inexpensive source in the UK would be builders 110V site transformers, they often have a 240-240 centre tapped transformer....

Uh, no, they're 55-0-55 secondaries.

[Electronics-Repairman]

A good inexpensive source in the UK would be builders 110V site transformers, they often have a 240-240 centre tapped transformer....

Uh, no, they're 55-0-55 secondaries.

I won't bother to even take the lid off the one in the garage, am I been lazy

[Monkeh]

A good inexpensive source in the UK would be builders 110V site transformers, they often have a 240-240 centre tapped transformer....

Uh, no, they're 55-0-55 secondaries.

I won't bother to even take the lid off the one in the garage, am I been lazy

Not really, they're not much use for isolation. They're 55-0-55 secondaries with the center tap hard wired to earth. Often potted.

[bance]

Not really, they're not much use for isolation. They're 55-0-55 secondaries with the center tap hard wired to earth. Often potted.

OOPS!