rebuilding transformer

How do I take a PC power supply transformer apart without breaking the core?

Hello there,

There is no way that i know of for most transformers because the windings are usually
varnished. This means you cant even unwind the
windings in most cases. The transformers
are usually dipped in varnish and then
baked in an oven to dry the varnish. This
makes the windings stick together so they
dont vibrate and also makes the whole
structure more thermally conductive.
You can sometimes add windings however, if
you can find room inside the core. You have
to wrap the new windings around the center part
of the core also.

I've taken several transformers apart by
cutting the windings off with a hacksaw.
Although it's not an easy task, you can
then wind your own turns around the core.
Before you do this though, it would be a
good idea to get an estimate of the
number of turns on the primary and the
typical driving voltage so you can estimate
your Bmax for the transformer so you can
determine how many turns you will need for
a given application.
I can tell you before you start though, plan
on spending LOTS of hours doing something like
this. I doubt it is worth it really, unless
you have a very pressing application or
something.
On the other hand, adding turns isnt that hard
as long as there is room in the core window.

It might help if you stated what you are trying to
do with this.

Good luck with your LED circuits,
Al

I have taken apart PC power supply transformers before, the challenge is not unwinding the windings, but getting the core out without breaking it.
I want to wind a flyback transformer to supply 1200v for a laser power supply.

Hello,

Ok then, good luck with it star.

BTW, if you can find an old tv laying around
you might be able to salvage the flyback
transformer too. This way you will have
what you need already?

Take care,
Al

A TV flyback is 25KV at a few ma.
This is fine for starting the tube, but tubes usually use about 2500V at 3-9ma(Oh yes, I do have a small flyback lying around).

Pre-manufactured epoxy potted laser power supplies that operate from 12Vdc or 120VAC can be purchased for $15-25 if you look around. Might be easier.

Having said that I made my own laser supply for a special HeNe tube. I used a 120V->600V tube type transformer with a voltage multiplier to produce 3600V @ 20mA, with a starter circuit to provide 25KV to strike the tube. It was not easy obtaining the high voltage components, and I fried a few during construction due to arcing. Not to mention the lethality of the voltages at those current levels. I'll suggest proceeding with a great deal of caution.

It sounds like you wish to build a high frequency switching type of power supply using ferrite cores from a PC switching supply. You'll have to use a lot of care in insulating the layers of the windings and then pot the thing in an appropriate epoxy or oil bath - without air bubbles - to prevent arcing in the windings. You'll also have fun finding high speed diodes that can withstand high voltage. Not a trivial project if done well.

I will use regular wire to wind the secondary.
I use electrical tape to insulate the winding.
The design is a flyback design, so I can use as little as a 1:10 ratio(I use a transistor from the computer power supply, which is good for at least 400v(I find the damper capacitor size with a SPICE simulation)).
I can use a microwave power diode or a string of 4007s for the rectifer.
I have a good scope for tuning the circuit.

Cool drawings Bart