[AMRadio] Varnish and potting of transformers

John Lawson jpl15 at panix.com
Sun Sep 18 13:17:49 EDT 2005

I have a little side-business rewinding and refurbing small DC motors and 
transformers for a couple of niche markets.

   To re-pot and re-varnish, currently I'm using a small (15" cube) vacuum 
curing oven that I found surplus on eBay and managed to buy cheap - in the 
$100 range. It's door is thick glass and seals against hi-temp silicone 
rubber, it goes to 450 deg and I can pull a nice vacuum on it with a small 
vane pump I also got on eBay - 26 or 26.5" is fine.

   You can also use one of those closed pressure-pots that painters use, 
they're about 5 gallons and have a lid with clamps - on a hot plate or 
wrapped with the heat-strips used to melting snow on your roof..

   Once you've soaked your transformer in whatever varnish or compound, it 
goes in the oven to bake, and the vacuum extracts all the air inclusions. 
You can also put the transformer core, in a container of impregnant, in 
the oven and jut pull the vacuum to fully process it, then bake it later.

   I also use the little oven to bake small things that I've re-painted... 
works very well for that, and certainly tends to ensure domestic 
tranquility when SWMBO opes her oven to bake a pizza and finds (and 
smells!!) three or four freshly-varnished armatures...

   Been there, done that, got the blody t-shirt.


John  KB6SCO

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