I have a transformer from an old 550watt computer power supply. To discover the pinout, do I simply just input a very small sine wave and measure the output? Since one side has two pins and the other has around 6 (some connected), do I assume that the one with two pins is the primary (mains) side? Also, at the top there is a two thicker wires coming out and soldered together. Are these ground, and if so what side are they grounded to?


If you look at the link the picture in the top right has a transformer with a white wire coming out the top. This is nearly identical to the transformer I have.

Thanks for any help.


http://www.isomatic.co.uk/

 

That's no mains transformer it's a SMPS transformer. The multiple outputs are the multiple taps it has, such as +12V, +5V, +3.3V, COM, -5V (sometimes) and -12V.

 

Yea, I kind of figured that the different ones were for the different computer voltages. A closer look reveals that although there is 6 pins, two pairs are connected only leaving what appears to be 4 taps. Regardless of those which I can discover with a scope, what do I do with the white connected ones coming from the top?
But, I thought I read that it is bad to test a smps transformer with no load connected. Is that right?

Thanks!

 

Those transformers are wound according to a given circuit. It will not work on other SMPS.
It will only work if you can duplicate the primary drive methods and secondary load regulation requirements.
An SMPS transformer can be only checked for it's inductance to a given circuit. Which varies from one type of SMPS to another

 

Bassman - please reassure us that you ARE NOT going to connect the primary winding to mains voltage!!!!!!!

But then again, if you don't reply it will tell us you have tried (and now can't see the monitor because of schrapnel wounds) ;-)

 

Thanks for the response. I guess this one isn't going to work then haha. I'm just looking for a used transformer that I can get +-12v for a power supply. That is all. Thanks for the info!

 

Yes for ±12V you will have to use an AC transformer designed for the job.

 

The transformers in a switcher are designed to operate at a high frequency (usually in the tens or hundreds of kHz. They won't work on 50/60Hz.
/mike