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omegalabs

Mon Jan 26 2009, 06:03PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

My friend show me this spray:

I think this is a helpful lacquer, with a dielectric strenght of 48kV/mm.

Herr Zapp

Mon Jan 26 2009, 06:51PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

omegalabs -

Any insulating coating applied to a Tesla coil secondary is likely to acquire an electrostatic charge during coil operation, and hold this charge long after the coil has stopped running. Even with coils that do not have a coating over the windings, the insulating varnish on the magnet wire itself can acquire a charge, as can the coil form, especially if it is plastic. I have received many good jolts when removing my 6" X 30" secondary from my coil after operation, and the secondary can deliver at least 3-4 good pops several minutes apart, depending on how dry the air is.

Nitrocellulose lacquer is a clear finish usually used on wooden musical instruments, and there's no reason I can think of why it shouldn't work well as a secondary coating. Your secondary will still retain an electrostatic charge if you overcoat the nitrocellulose lacquer with polyurethane, or any other insulating coating.

After building a number of secondary coils and coating them with many coats of conventional solvent-based varnish, I switched to clear 2-part epoxy resin, and have now used this material for almost 10 years. I'm firmly convinced that it is the best material to use, from the standpoint of appearance, improved resistance to secondary arcing or insulation breakdown, mechanical protection of the windings, and ease of application. Correctly applied, one coat of epoxy can give a coating thickness of .020" (.5mm) or greater, and gives a perfectly glass-smooth surface finish.

Here is a write-up on the application process I use. Note that it is essential to have some sort of motorized fixture to mount the coil on so it can be rotated at a slow speed for several hours while the epoxy cures.

Herr Zapp

Tom540

Mon Jan 26 2009, 10:35PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

Water based looks nice dries fast but is not as durable. If you have a heat lamp you could almost re coat it every our or even less. It gets ugly after a few years and can be peeled off. its good for quickie coils or test secondaries but if you want something nice that will last don't use it.

Non water based stuff like varnish, varathane is good middle ground stuff. There's a ton of different kinds. It wont last forever either and needs multiple coats. But is decent.

Furniture epoxy is the best. I use it all the time. It needs one coat and after 3 days is 100% dry. It is super durable and looks nicer than the other three with less effort. It's also pretty water proof as far as I've seen. I coated a homemade coaster with it. The water has had no effect on it so far. There are some places in my garage where ive dripped it on the floor and the spots arent even scratched much. Only bad thing is its more expensive, but then again you only need one coat which is equal to 60 coats of varnish.

Herr Zapp

Tue Jan 27 2009, 06:37PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

OOPS -

The .pdf file attachment with the detailed procedure for applying epoxy resin to a secondary coil somehow got dropped from my previous post. Here it is again:

Herr Zapp
]using_2- part_epoxy_resin_for_coating_tesla_coil_secondary. pdf.pdf[/file]

Mathias

Wed Jan 28 2009, 10:57AM

Registered Member #1381 Joined: Fri Mar 07 2008, 05:24PM
Location: Hungary
Posts: 74

Hello :P

Well I found a great replacement for that minwax stuff here in hungary , its called bona mega 100% polyurethene water based (4200 ft /1L) . Works and looks great. If used as instucted :)

Btw dont use aerosol type coatings the propellent gas gets traped under the coat and when that begins to dry the miniture bubbles "expand"
(or just case of another factor, becase i sprayed the stuff on outside in the cold , later on (when the smell was gone :P) i brought it inside after some hours the bubbles appeared)

omegalabs

Wed Jan 28 2009, 06:17PM

Registered Member #1521 Joined: Thu Jun 05 2008, 10:46AM
Location: Hungary
Posts: 128

Mathias wrote ...

Hello :P

Well I found a great replacement for that minwax stuff here in hungary , its called bona mega 100% polyurethene water based (4200 ft /1L) . Works and looks great. If used as instucted :)

Btw dont use aerosol type coatings the propellent gas gets traped under the coat and when that begins to dry the miniture bubbles "expand"
(or just case of another factor, becase i sprayed the stuff on outside in the cold , later on (when the smell was gone :P) i brought it inside after some hours the bubbles appeared)

This shop is just near my scool :) . I have searched for epoxy but I found only expensive ones.

Now, the final question. Is this lacquer good, or should I keep trying to find a good epoxy resin?

Herr Zapp

Wed Jan 28 2009, 10:53PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

omegalabs -

Glyptal Inc manufactures a wide range of inductrial paints and coatings, including several nitrocellulose lacquers that are advertised as having "high dielectric strength and arc resistance". See Industrial Topcoats, types 7600 and 2496 at:

So, generally speaking, there is nothing to indicate that your nitrocellulose lacquer be unsuitable for a overcoating secondary coil.

Just finish building your coil, and fire it up. I don't think the secondary coating will be a problem.

Regards,
Herr Zapp

MOT_man

Thu Jan 29 2009, 07:01AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Nitro lacquer is pretty brittle stuff when dry. Over time it will flake off as it become acidic in the presence of UV light. This is why wood workers prefer polyurethane finishes as they are flexible and have better bonding properties.

Herr Zapp

Thu Jan 29 2009, 05:45PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

MOT man -

Can you provide a link to your source of information for the "becomes acidic in the presence of UV light" statement, as applicable to nitrocellulose lacquer coatings?

Thanks!
Herr Zapp

MOT_man

Fri Jan 30 2009, 07:49AM

Registered Member #1127 Joined: Mon Nov 19 2007, 12:08AM
Location:
Posts: 139

Stanford University Press -
"nitrocellulose, an ingredient found in polishes & lacquers that turns yellow when exposed to UV and becomes brittle"

R. Fairfield - Int. Woodworker Association
"UV exposure doesn't do much for a nitrocellulose lacquer except make it turn an amber color and become brittle."

PCRC
"Nitrocellulose lacquers are notorious for yellowing, if at all possible you may want to consider using a cellulose acetate butyrate (CAB) acrylic blend. These types of lacquers have been used in the automotive paint industry for many, many years with minimal color change."

Wood Working.com
"By itself, nitrocellulose is very brittle and very hard."

So from all the information I've gathered - and of course speaking with local paint shops and Industrial Transformer winding shops - the verdict is out. Nitrocellulose lacquer works well when it is combined with other Alkyds. By itself as a pure lacquer it is extremely prone to yellowing in the presence of UV light - this photochemical reaction also effects the strength and flexibility of the lacquer as well. The nitrate breaks down chemically in the varnish due to oxidation. The oxidation process - produces an acidic release in the varnish. This is why Polyurethane is a far better product - it isn't nearly as inflexible or prone to photochemical breakdown as NC. If you would like to speak with General Paint, CANADA or Cloverdale paints, CANADA they can verify this information too.

I wouldn't use straight Nitro lacquer on my coil. If it was combined with some other Alkyd then - possibly.

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