James Thompson kirjoitti:
Has anyone re-wound a power transformer with good results?
I have salvaged some big transformers from microwave ovens, and cut the
secondary winding out of it. Then re-wound it with 14 guage till getting
enough turns to produce about 20 volts. Problem is the thing gets hot even
without a load on it.
Is there something I am overlooking? Thanks.


Hi !

That transformer is working in saturation.
Maybe you can see a welded line in the iron going over the plates.
Maybe not. It depends on design

Saturation guarantees good enough regulation for magnetron HT.
Also so called line conditioners and AC stabilizers are working with
saturated core.

Saturated cores are getting warm even withouth any load.
Added load doesn't warm up them remarcable any more.

Maybe saturation is an advantage for you because of regulation phenomena.
Test regulation with variac in input but use some load in secondary !

Line conditioner behaves so that in certain lowered input voltage the
saturation stops and output trends to drop.
To guarantee stabilization and conditioning they need some load all the
time (5 % of max allowed power is normally OK)
Line conditioners are normally working in resonance principle.
Therefore they have a nice flywheel efect. Gaps or glitches in line
sinus form are removed

73 ! Risto, OH2BT