Secondary coil coating/varnish type
Dr. Dark Current, Wed Feb 29 2012, 02:09PMHi,
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?
Re: Secondary coil coating/varnish type
Mads Barnkob, Wed Feb 29 2012, 02:31PM
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.
Mads Barnkob, Wed Feb 29 2012, 02:31PM
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.
Re: Secondary coil coating/varnish type
Killa-X, Wed Feb 29 2012, 08:54PM
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.
Killa-X, Wed Feb 29 2012, 08:54PM
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.
Re: Secondary coil coating/varnish type
Sulaiman, Wed Feb 29 2012, 09:45PM
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.
Sulaiman, Wed Feb 29 2012, 09:45PM
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.
Re: Secondary coil coating/varnish type
Dr. Dark Current, Wed Feb 29 2012, 10:28PM
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...
Dr. Dark Current, Wed Feb 29 2012, 10:28PM
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...
Re: Secondary coil coating/varnish type
Mads Barnkob, Wed Feb 29 2012, 11:25PM
Another factor would also be the cooling, a open coil will have a much larger surface to dissipate heat from than a varnished coil.
Mads Barnkob, Wed Feb 29 2012, 11:25PM
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...
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.
Re: Secondary coil coating/varnish type
Tetris, Wed Feb 29 2012, 11:31PM
Minwax Polycrylic High Gloss. :D you can get it at Lowes. Killa-X was the one who reccomended it for me.
Tetris, Wed Feb 29 2012, 11:31PM
Minwax Polycrylic High Gloss. :D you can get it at Lowes. Killa-X was the one who reccomended it for me.
Re: Secondary coil coating/varnish type
Sulaiman, Thu Mar 01 2012, 01:15PM
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'
Sulaiman, Thu Mar 01 2012, 01:15PM
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'
Re: Secondary coil coating/varnish type
Goodchild, Thu Mar 01 2012, 04:43PM
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.
Goodchild, Thu Mar 01 2012, 04:43PM
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.
Re: Secondary coil coating/varnish type
Sparrow338, Thu Mar 01 2012, 06:07PM
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.
Sparrow338, Thu Mar 01 2012, 06:07PM
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.
Re: Secondary coil coating/varnish type
Fulmen, Thu Mar 01 2012, 10:54PM
Sure you can:
Great stuff, works fine for both lamination and coating.
Fulmen, Thu Mar 01 2012, 10:54PM
Mads Barnkob wrote ...
I can not get hold of epoxy varnish in Denmark.
I can not get hold of epoxy varnish in Denmark.
Sure you can:
Great stuff, works fine for both lamination and coating.
Re: Secondary coil coating/varnish type
ajacks504, Mon Mar 05 2012, 07:08PM
I used Humiseal 1B31. It has pretty decent dielectric properties, but the coolest thing about it is that it fluoresces under UV light, which makes it glow when the coil runs ;)
ajacks504, Mon Mar 05 2012, 07:08PM
I used Humiseal 1B31. It has pretty decent dielectric properties, but the coolest thing about it is that it fluoresces under UV light, which makes it glow when the coil runs ;)
Re: Secondary coil coating/varnish type
Herr Zapp, Mon Mar 05 2012, 09:17PM
Dr. Dark Current -
There's no varnish that can provide the thickness, ruggedness, insulation capabilities and appearance that can be obtained with a single coat of two-part clear epoxy. Done carefully, the finished secondary will look like it's encased in a glass sleeve. Over the past 10 years I've coated secondary coils of many different sizes with epoxy, and I'd NEVER go back to varnish.
Be careful of the type of epoxy you select. Do not use "laminating" epoxy, which is intended for use in composite construction along with layers of fiberglass, carbon, fiber, etc. The laminating grade epoxies usually do not cure to a hard, tack-free surface. You want a a material that's intended for use as a protective top-coat, and allows surfaces exposed to air to fully cure. In the US, Environmental Technonogies offers a product (Envirotex Lite) that works great. See:
I've previously posted a fairly detailed procedure for preparing and applying a two-part epoxy finish, see the thread "Clear epoxy secondary coatings". About halfway down the page is my post with the link to the procedure:
Herr Zapp
Herr Zapp, Mon Mar 05 2012, 09:17PM
Dr. Dark Current -
There's no varnish that can provide the thickness, ruggedness, insulation capabilities and appearance that can be obtained with a single coat of two-part clear epoxy. Done carefully, the finished secondary will look like it's encased in a glass sleeve. Over the past 10 years I've coated secondary coils of many different sizes with epoxy, and I'd NEVER go back to varnish.
Be careful of the type of epoxy you select. Do not use "laminating" epoxy, which is intended for use in composite construction along with layers of fiberglass, carbon, fiber, etc. The laminating grade epoxies usually do not cure to a hard, tack-free surface. You want a a material that's intended for use as a protective top-coat, and allows surfaces exposed to air to fully cure. In the US, Environmental Technonogies offers a product (Envirotex Lite) that works great. See:
I've previously posted a fairly detailed procedure for preparing and applying a two-part epoxy finish, see the thread "Clear epoxy secondary coatings". About halfway down the page is my post with the link to the procedure:
Herr Zapp
Re: Secondary coil coating/varnish type
Fulmen, Thu Mar 08 2012, 09:07AM
Fulmen, Thu Mar 08 2012, 09:07AM
Herr Zapp wrote ...
The laminating grade epoxies usually do not cure to a hard, tack-free surface.
I haven't tried enough different brands to say anything about them in general, but the epoxy I recommended (Biltema-brand) does cure to a hard finish eventually.The laminating grade epoxies usually do not cure to a hard, tack-free surface.
Re: Secondary coil coating/varnish type
PhilGood, Fri Mar 09 2012, 06:18AM
Btw thanks Herr Zapp for the detailed "How to apply" ;)
Did you happen to prepare too much and have a rest which hardens in the mixing can ? Is it still as a glass block ?
I wonder if it could be used for components molding.
PhilGood, Fri Mar 09 2012, 06:18AM
Herr Zapp wrote ...
Environmental Technonogies offers a product (Envirotex Lite) that works great.
This Envirotex Lite compound seems really interesting...Environmental Technonogies offers a product (Envirotex Lite) that works great.
Btw thanks Herr Zapp for the detailed "How to apply" ;)
Did you happen to prepare too much and have a rest which hardens in the mixing can ? Is it still as a glass block ?
I wonder if it could be used for components molding.
Re: Secondary coil coating/varnish type
Herr Zapp, Fri Mar 09 2012, 08:49PM
PhilGood -
Yes, any unused material left in the bottom of your mixing cup will harden into a clear, hard disk.
If you set up everything before hand, there's no reason not to use any residual material as a potting compound, but it's difficult to know exactly how much residual resin there'll be until you are done coating the secondary.
Herr Zapp
Herr Zapp, Fri Mar 09 2012, 08:49PM
PhilGood -
Yes, any unused material left in the bottom of your mixing cup will harden into a clear, hard disk.
If you set up everything before hand, there's no reason not to use any residual material as a potting compound, but it's difficult to know exactly how much residual resin there'll be until you are done coating the secondary.
Herr Zapp
Re: Secondary coil coating/varnish type
PhilGood, Sat Mar 10 2012, 12:36AM
Sounds good, thanks Herr Zapp
In fact my idea is to use this compound on purpose for molding compenents.
For examples, a HV Diode, let's say we put together 100x 1N4007 in serie on two layers of 50 this way :
ooooo...ooooo
ooooo...ooooo
we get an assembly of approx. 10 x 10 x 130 mm
molden this in a block of this coumpound and we get a very nice looking 100kV 1A Diode.
Of course I also plan to try this compound for secondaries coating
PhilGood, Sat Mar 10 2012, 12:36AM
Sounds good, thanks Herr Zapp
In fact my idea is to use this compound on purpose for molding compenents.
For examples, a HV Diode, let's say we put together 100x 1N4007 in serie on two layers of 50 this way :
ooooo...ooooo
ooooo...ooooo
we get an assembly of approx. 10 x 10 x 130 mm
molden this in a block of this coumpound and we get a very nice looking 100kV 1A Diode.
Of course I also plan to try this compound for secondaries coating
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