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SMPS transformer varnish
SMPS transformer varnish
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Old 8th January 2020, 07:31 PM   #11
Osvaldo de Banfield is online now Osvaldo de Banfield  Argentina
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I do it outside my house, outdoor as it is said.
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Old 8th January 2020, 07:37 PM   #12
Kay Pirinha is offline Kay Pirinha  Germany
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Of course. I hope you're wearing gloves, 'cause chloroform easily penetrates the skin?
Best regards!
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Old 8th January 2020, 08:04 PM   #13
SemperFi is offline SemperFi  Wake Island
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I would use a marine lacquer or varnish which remains a little elastic.
Dont use epoxy on ferrite core traffos since it becomes too hard and the core can break during use.
Air has dialectric constant of about one, lacquer and paints have at least 2, probably 3-4. So after lacquer the capacitance will increase by the same factor. That probably does not matter but must be concidered.
You should not get a more quiet SMPS b/c the frequencies are too high to hear anyways. But there are good reasons to impregnate a traffo. Google.
I canabalized a vacuum pump from an old refrigderator. A small bucket just big enough for the traffo. Fill up varnish. Have a lid with a tube to the vacuum pump. Vacuum. The air bubbles out of all crevises and varnish is sucked into all gaps. Done.
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Old 8th January 2020, 08:08 PM   #14
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by SemperFi View Post
I canabalized a vacuum pump from an old refrigderator.
Do you mean the fridge's compressor?
Best regards!
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Old 8th January 2020, 08:22 PM   #15
wrenchone is offline wrenchone  United States
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Varnish impregnation certainly does affect the intra and interwinding capacitance of a transformer. It has been documented at my workplace countless times by measuring the transformer primary resonant frequency before and after varnishing. The resonant frequency always shifts substantially down after varnishing, indicating an increase in winding capacitance.

If I were going to varnish a transformer using stuff just available from the local hardware store, I would just use a good polyurethane varnish with no stain.. For a "poor man's vacuum impregnation" method, heat the finished transformer up to ~100C for an hour or so, then plunge it into the vanish. The hot air inside the transformer will cool, shrink, and draw the varnish father into the windings than a simple room-temperature dip would accomplish. I try not no vacuum impregnate using a solvent-based varnish, as it tends to boil off the solvent and make a mess.
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Old 8th January 2020, 09:00 PM   #16
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by wrenchone View Post
I try not no vacuum impregnate using a solvent-based varnish, as it tends to boil off the solvent and make a mess.
Good objection!
Best regards!
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Old 8th January 2020, 09:21 PM   #17
MorbidFractal is offline MorbidFractal
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Quote:
Originally Posted by Kay Pirinha View Post
Do you mean the fridge's compressor?
Best regards!
These days posh fridges suck to close their doors properly and remove internal air/moisture. Don't know what sort of vacuum they achieve but perhaps that is what SemperFi was referring to. I assume it is a unit that is separate to the compressor.
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Old 8th January 2020, 09:55 PM   #18
SemperFi is offline SemperFi  Wake Island
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I think you are correct it is the compressor but I use the wrong end which sucks. It does a good job. I mainly use it for composite layups when making parts but have also used it for traffo vacuum impregs.
Lots of info on web regarding diy vacuum pump from old fridges.
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Old 9th January 2020, 01:15 AM   #19
PRR is offline PRR  United States
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Quote:
Originally Posted by Kay Pirinha View Post
> I canabalized a vacuum pump from an old refrigderator.
Do you mean the fridge's compressor?
The standard Freon pump in a refrigerator will pull a pretty good vacuum. It is not the greatest vacuum pump around, and may not last long sucking dirty air, but "dead reefers" (switches or wires; often the compressor still works) are nearly free in wealthy countries.
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