James Thompson wrote:
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.

I found the same thing when I rewound one a few years back.
Apparently the primary is saturated so it will draw 4 or 5 amps with
the secondary loaded or unloaded. This provides some voltage
regulation.
I should have taken a variac and ran a V/I curve from 0 volts to the
point saturation occurs and the current starts to rise. That would
prove that the transformer operates in saturation.
My microwave is rated for continous operation at full load, so
apparently the transformer doesn't get hot enough to let the smoke out,
but it does get hot.

Gary N4AST