Testing isolation in SMPS transformers

[eem2am]

hello.

For 230VAC input , offline flyback transformers (fully isolated), how do you test to see if the transformer provides the necessary degree of isolation between primary and secondary?

 

[Orson Cart]

Normally a "flash tester" is used - a small variac driving a stepup Tx with an output up to 4kV AC and a shut off ckt to disconnect the o/p if the current exceeds 5mA (for example) on the o/p, connect across the pri - sec windings
Regards, Orson Cart.

 

[eem2am]

Hi,

I am wondering why it needs to be AC?

Why not just connect the equipment to a DC voltage at the same value as the peak of the AC?

 

[mtwieg]

It doesn't always have to be AC, but AC hipot testers are easier to make (just a big step up transformer and a variac) and are cheaper. Hipot testing with AC is usually sufficient, but sometimes testing with DC may be a good idea.