DIY vacuum-pump? (for vacuum impregnating)

On Thu, 20 Sep 2007 08:07:55 +0200, Nick Mueller


Not sure what "PU in water" means but if it needs 120..140 deg C cure it sounds like the right stuff.
Jim
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snipped-for-privacy@yahoo.com wrote:

PU is PolyUrethane and water is DHMO. :-) It is polyester (and not PU as I wrote) suspended/emulsified in water. Can be thinned with tap water. Like those Aqua-paints. Solvent free. That stuff doesn't get try (or verrrry slowly) without heat.
It seems to be "Dolphon BC365" sold under a different name. Dolph's has hits with "Aquaterm", but maybe that comes from their Italian sister. <http://dolphs.com/techtips_1099.cfm
Nick
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On Thu, 20 Sep 2007 13:58:15 +0200, Nick Mueller

I've never used this stuff but anything containing with water is normally unsuitable as an impregnant.With oil filled transformers very great care is taken to see that the oil is really dry and free from even the tiny amount that it can naturally absorb! Water contamination both reduces the dielectric breakdown strength and can cause long term corrosion of fine wires.
Your varnish is clearly engineered for impregnation purposes but I'm not too sure about its long term compatibility with very fine wires. Everything depends on getting rid of the residual water. This has to exit as vapour from the centre of your windings so you need a very good long high temperature vacuum bake.
For low temperature experimental work wax is pretty convenient.
Jim
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snipped-for-privacy@yahoo.com wrote:

Me too! :-)

It is sold as impregnating varnish. The dielectric strength dry/whet is 1900/1850 Volts/mil. Funny, quite the same strength with water in it. But I realized that this varnish simply might be the wrong type and I need something different. :-( They sell different stuff for VPI. The one I have is not listed for VPI. That wasn't clear when I ordered it. Anybody needs 0.75l of varnish. :-)
OK, I'll look for something different, but I'll give it two more tries with the better vacuum. Maybe the water is boiling out and I can re-apply pressure with the coil completely submerged to force it back into.

:-( I didn't intend to heat the vacuum chamber.
Nick
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On Fri, 07 Sep 2007 20:13:59 +0200, Nick Mueller

Edwards are the classic vacuum pump manufacturer and turn up fairly frequently on Ebay. However they're over kill for a one off impregnation cycle.
For occasional use, provided you've got a zero leak setup, an old sealed unit refrigerator compressor run as a vacuum pump is good enough. It can also be further improved by using your injector pump as a backing pump on the refrigerator outlet.
Jim
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I have some sort of vacuum pump driven by a single phase motor that is not used. I haven't studied the thread properly as its too early. Will photograph it today. Bob
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