Creating cheap custom power transformers by reusing a microwave oven transformer

Microwave oven transformers can easily be found discarded and reused to make a powerful custom transformer.  The ability to easily reuse the transformer comes from the primary and secondary windings being physically isolated from each other on the metal core.

The aim is to remove the secondary windings as cleanly as possible and wind a custom winding using enameled wire.  In my case for every one loop around the core gets one volt, the thicker the wire, the more current that can be supplied.

There are three windings on a microwave transformer, one primary and two secondaries.  In the pictures below, the primary is on the bottom and the secondaries are on the top.
The primary has hundreds of turns of thicker wire, do not modify this, keep it pristine.
The high voltage secondary, with thousands of turns of fine wire, we do not need this.
The six volt filament winding made from cloth insulated wire, we do not need this.

Removing the secondary is relatively easy. 

  • Clamp the transformer in a vice and using a hacksaw, cut one end of the secondary off.  Be careful that the saw does not cut into the primary at the end and try to avoid cutting the paper inner paper insulator.
  • Spray penetrating oil into the exposed wire in the transformer, this will help in the next stage.
  • Using a large drift and hammer, bash out the rest of the wire a bit from both sides at a time until it comes out like a horseshoe.  If the drift is too small, it will compress the wire and make it impossible to remove easily.
  • Once removed, clean all metal filings and make sure that the mylar paper insulator is intact, repair using insulating tape if required.  You do not want exposed metal cutting into the wire while winding.
  • Now using enameled wire, rewind to your own specifications.  The image below is a 4 volt ugly monster with several windings in parallel.

Remember that this transformer will hum like a microwave when in use.  It will draw lots of power. 
It will require some kind of forced air cooling to keep it happy.  Reuse the microwave fan…
Don’t attempt to take the laminations apart.  They are often welded. 
Best to source a transformer from a larger microwave oven, bigger = more power.

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