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Forums
4hv.org :: Forums :: Tesla Coils
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Secondary coil coating/varnish type

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Dr. Dark Current
Wed Feb 29 2012, 02:09PM Print
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hi,
what kind of clear varnish do you use for your Tesla coils? Do you know which type has the lowest dielectric losses at the usual TC frequencies?
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Mads Barnkob
Wed Feb 29 2012, 02:31PM
Mads Barnkob Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
polyurethane varnish is what I have the best results with, I can not get hold of epoxy varnish in Denmark.

7 - 10 layers polyurethane varnish will give a nice finish.

I have also tried oil based varnishes, works just as well, but does not look as good.
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Killa-X
Wed Feb 29 2012, 08:54PM
Killa-X Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
I second Mads Barnkob. I use to use poly acrylic, as it did wonders for my first coil, but i found out if you want mirror finish, polyurethane is the best. I go for the see-yourself-finish...I typically do 7-10 layers, sand with 600... repeat that 3 times, then 7-10 layers -- sand with 800, repeat 3 times... then work my way to 1500 grit, repeat 3 times, final product is mirror. Lot of work, but its worth it for me, because i love the finish :)

http://i.imgur.com/cxb1H.jpg Work in progress.
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Sulaiman
Wed Feb 29 2012, 09:45PM
Sulaiman Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Liquid Polyurethane "floor varnish' works well
and a gloss finish can be achieved
with a 'thinned' layer first to penetrate the windings
then a couple of thick layers without sanding
...need to mount the coil on a motorised device to keep the coil rotating whilst drying
OR apply many thin coats.

'Yacht varnish' gives a nice hard finish.

A thin coating is probably better than a thick one as quite a lot of 'static' charge can accumulate on a thick varnish layer and 'zap' you, not dangerous but annoying.

A thick coating does look better and provide protection against accidental 'nicks' in the wire/winding.

P.S. I don't think that the dielectric loss of the varnish is important at all.
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Dr. Dark Current
Wed Feb 29 2012, 10:28PM
Dr. Dark Current Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Thanks for the replies. As for the losses, I was trying to design an RF choke for a 30 MHz oscillator. The first coil which I dipped in varnish was burning hot, the second one was the same but parafin wax coated, it was better but still hot. The last one was wound with a gap between the turns and this one remains cool during operation.
So there are indeed some losses in the varnish, but if they're important at usual TC frequencies, I don't know...
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Mads Barnkob
Wed Feb 29 2012, 11:25PM
Mads Barnkob Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
Dr. Dark Current wrote ...

Thanks for the replies. As for the losses, I was trying to design an RF choke for a 30 MHz oscillator. The first coil which I dipped in varnish was burning hot, the second one was the same but parafin wax coated, it was better but still hot. The last one was wound with a gap between the turns and this one remains cool during operation.
So there are indeed some losses in the varnish, but if they're important at usual TC frequencies, I don't know...

Another factor would also be the cooling, a open coil will have a much larger surface to dissipate heat from than a varnished coil.
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Tetris
Wed Feb 29 2012, 11:31PM
Tetris Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660
Minwax Polycrylic High Gloss. :D you can get it at Lowes. Killa-X was the one who reccomended it for me.
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Sulaiman
Thu Mar 01 2012, 01:15PM
Sulaiman Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
For the same wire, a close wound coil will get much hotter than a coil wound with one wire diameter inter-turn space due to 'proximity effect'
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Goodchild
Thu Mar 01 2012, 04:43PM
Goodchild Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
I used to use polyurethane varnish, but after working with epoxy for a while now I much prefer it over poly for a couple of reasons. First of all you only need one coat and it's a rock hard hard coating that stands up to racing sparks very well.

5013593786 5a7b962e14
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Sparrow338
Thu Mar 01 2012, 06:07PM
Sparrow338 Registered Member #661 Joined: Sat Apr 21 2007, 03:17AM
Location: Ventura, CA
Posts: 41
I've had good luck with this stuff:
http://www.lowes.com/ProductDisplay?partNumber=147376-1149-5050080&langId=-1&storeId=10151&productId=3151089&catalogId=10051&cmRelshp=sim&rel=nofollow&cId=PDIO1

It you end up using it make sure you have a blow dryer handy for getting rid of the bubbles that form when poured. Suppose one could also de-gas it by putting it in a vacuum before pouring it.
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