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Old 17th July 2013, 01:06 PM   #1
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Default Potting Wax?

I have about 20 of these transformers I got a deal on from a surplus center that I have been using for preamps. The issue is that they tend to be on the buzzy side if I do not modify them a bit with something to damp the resonance in the top bell. (Through hole design). I am using maybe 1/15th the current capability, so they tune all day long at just over room temp.

I was using hot glue to fill the top bell and then pressing them together, but: A) hard to measure if I have enough or to small of an amount. B) it does not really seep into the windings the way something more fluid would.

So, I went to the grocery store and bought some paraffin wax. I always make a high density foam gasket when I put the top bells on for additional damping, so they are sealed for the most part. I flipped the transformer over to the bottom and cut away the bottom paper exposing the leads and used a heat gun to melt and drip the wax into the transformer. Voila! Much quieter than hot glue, but at a lower melting point. I'm not worried about the operation heat, but down south here, a garage can get almost as hot as the melting point of the wax.

After my drawn out explanation of what I need it for what does Cary use to pot their transformers which run significantly hotter than the ones I use? I found some microcrystalline waxes that melt at a hotter temp, but the Cary wax looks more like a bees wax with something added maybe?

Thanks for any assistance!

Blair
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Old 17th July 2013, 01:15 PM   #2
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I'd guess that usual potting involves some resin or epoxy, maybe even with enhanced thermal conductivity. I'd be hesitant to use wax, as it has a rather low fire point.

Here's a short piece on potting transformers with resin: Designing Ampiifiers, Part 3
And something from this board as well: Potting transformers
And a story from Cary: Cary Audio Design - Transformer Potting
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Old 17th July 2013, 06:10 PM   #3
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Parafinwax melts already at 37 degrees Celcius. You need stearic acid, if you have the right stearic acid it melts at 70 degrees celcius

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Originally Posted by deicide67 View Post
I have about 20 of these transformers I got a deal on from a surplus center that I have been using for preamps. The issue is that they tend to be on the buzzy side if I do not modify them a bit with something to damp the resonance in the top bell. (Through hole design). I am using maybe 1/15th the current capability, so they tune all day long at just over room temp.

I was using hot glue to fill the top bell and then pressing them together, but: A) hard to measure if I have enough or to small of an amount. B) it does not really seep into the windings the way something more fluid would.

So, I went to the grocery store and bought some paraffin wax. I always make a high density foam gasket when I put the top bells on for additional damping, so they are sealed for the most part. I flipped the transformer over to the bottom and cut away the bottom paper exposing the leads and used a heat gun to melt and drip the wax into the transformer. Voila! Much quieter than hot glue, but at a lower melting point. I'm not worried about the operation heat, but down south here, a garage can get almost as hot as the melting point of the wax.

After my drawn out explanation of what I need it for what does Cary use to pot their transformers which run significantly hotter than the ones I use? I found some microcrystalline waxes that melt at a hotter temp, but the Cary wax looks more like a bees wax with something added maybe?

Thanks for any assistance!

Blair
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Old 17th July 2013, 11:53 PM   #4
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Is the acid a wax additive for stability, or does it melt down into a liquid?

The fiberglass type resin isn't a bad idea, but it is pretty viscous and I don't think it would seep in as well as a wax.
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Old 18th July 2013, 01:15 AM   #5
jjman is offline jjman  United States
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I've read of varnish being used. Viscosity is high, dries hard and won't melt.
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Old 18th July 2013, 01:26 AM   #6
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If you check on the web for suppliers to candle-makers, there are three grades of paraffin wax with different melting points. The stuff generally used for canning is probably the lowest melting grade.

Edit - a brief look at one candle maker's site listed their highest melting wax at 163F - you might find some higher melting waxes with a longer search.

Last edited by wrenchone; 18th July 2013 at 01:31 AM.
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Old 18th July 2013, 01:59 AM   #7
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I have done many searches, and found a few microcrystalline waxes with 90C / 194F melt temps. At ~8-10 bucks a pound.

Some look like what Cary uses. Beefed up tan colored beeswax look.
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Old 18th July 2013, 02:04 AM   #8
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Beeswax is what Cary uses, it is not flammable. I use it too this is where i get it

Pure Beeswax, Dadant & Sons Beekeeping Supplies and Candles


Best of luck

Peter
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Old 18th July 2013, 06:51 AM   #9
ChrisA is offline ChrisA  United States
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Historically, varnish is used but it is not just the standard marine spar varnish you'd paint on wood. It is special kind made for transformers. They usually apply it in a vacuum. The Vacuum pulls the air out from between the wires and lets the varnish in. Then the transformer is baked in a low oven. The other historic method is to use wax but it makes a mess if the transformer ever overheats and is not cheaper than varnish
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Old 18th July 2013, 07:56 AM   #10
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Beeswax, as far as I've seen, melts at a lower temp than the microcrystalline wax previously mentioned - this might not be much of an issue for an output transformer, but important for power transformers. Beeswax chips are also readily available, and may be cheaper than the slabs. Anything that damps the output transformers and keeps them from singing is probably a good idea. Mine always sing when I do a square wave test.

Varnishing is also a good idea it displaces air from the windings (improving breakdown voltage) and preventing the lams from rusting, but it doesn't damp the transformers completely. Dolph's make a good series of varnishes for transformers. I use BC-359 at work for SMPS transformers. Transformers using paper in between windings should be varnished, as the paper can be hygroscopic otherwise, and will have a low thermal rating without varnish impregnation.
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