Secondary varnish / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Secondary varnish

Move Thread

LAN_403

flannelhead

Mon May 26 2008, 03:23PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

What kind of varnishes do you use for your secondaries? I've done one secondary with water-based varnish, but I thought oil-based would look nicer. Has anyone used it? I thought with thinner wires (<0.1mm) it could have some undesirable effects on the enamel coating of the wire.

Also how many layers of varnish do you usually apply? Do you sand it before applying a new layer?

Dago

Mon May 26 2008, 03:32PM

Registered Member #538 Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181

I've used clear polyurethane lacquer which worked fine. Didnt sand and I put 4-5 coats which was too few because I can still feel the windings with my fingernail but I guess it doesnt really matter.

quicksilver

Mon May 26 2008, 03:55PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I have used the same thing (polyurethanes) with no problems. However my experience is VERY limited. I don't believe it would have an undesirable effect on the existing varnish due to the dry existing material having a limited time to solvent exposure via the poly application. However there may be a difference between the application process. If one were to spray rather than brush the material I doubt that it would create a solvent effect due to limited physical mixing. If one were to use a brush and apply continual contact pressure there may be some solvent effect (but I doubt it would break down the existing insulation between the coiled wire.)
Perhaps a valuable question to ask those with long term experience / knowledge would be: "Is there ANY finish or varnish that would be a BAD idea (and why)?"

Once I had heard that certain black materials used for secondary tubes had carbon in them making them a poor choice. (I didn't follow up on it & probably should have to determine whether it was rumor or had merit.)

There are idiosyncrasies in much of this that is tough to find out about unless you can get those with experience to expound on the idea from a wider perspective....(IMO)

Alexandre

Mon May 26 2008, 06:06PM

Registered Member #1228 Joined: Tue Jan 15 2008, 01:08AM
Location: Curitiba, Brazil
Posts: 162

I use EPOXIs, has no problem of isolation, isolating very good, but take about 24hrs to dry, and if you have to do some fix in the coil, it is virtually impossible, because they stick really very good.

But it is the best insulator that already found.

HV Enthusiast

Mon May 26 2008, 08:35PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

I've used polyurethane finish, shellac, and two-part epoxy.

Two-part epoxy is great to use, but is pretty nasty stuff and requires a lot of protective gear to use safely, although about 99.9% of hobbyists disregard this safety tidbit and just use it with bare hands, etc... (Epoxy resin / hardener is a very powerful skin sensitizer and once your skin becomes sensitizes, i.e. allergic, you can kiss your epoxy days over - so its always best to protect skin / etc...)

Polyurethane is good, but does discolor and flake with time.

Shellac is another alternative and some of the Tesla masters swear by it, especially for large secondaries.

Shaun

Tue May 27 2008, 04:24AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

I use two-part epoxy, but the stuff I have is a little too viscous, so it was very tough for me to find a way to get a smooth coat. Unless you have very thin epoxy (most kinds are exactly the opposite), I wouldn't recommend it.

Herr Zapp

Tue May 27 2008, 06:10AM

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

I've used two-part epoxy resin to cost secondary coils for more than ten years (over a dozen coils), and find it far, FAR superior to any varnish or lacquer type coating. Correctly applied, in a single application you can get a coating at least .030-.050" thick, which would take ten or more coats of varnish to achieve. A single heavy coat of epoxy will create the appearance that the windings are encased in a thick, flawless, high-gloss glass sleeve.

With a little care, there should be little chance for skin contact with the epoxy resin (which can cause a rash in sensitive individuals), but you can always wear gloves for more protection. It is absolutely necessary to have a motorized winding fixture that can rotate the secondary at a few RPM (3-10 RPM, depending on secondary diameter) during application of the resin, and keep it rotating while the epoxy cures. The epoxy I use is a medium viscosity product (about like heavy corn or maple syrup) sold in the US for coating tables and counter-tops. The manufacturer is Environmantal Technology, Inc (

), and the product is "Envirotex Lite". This material has at least a 45 minute pot life, and cures in 8 hours or less, depending on ambient temperature. After final curing the material is very slightly flexible, not brittle like many other polyester and epoxy resins. I've had secondary coils coated with this stuff kicking around for years, and none of them has suffered any cracking, crazing, chipping, delamination, etc. Aside from providing great protection to the windings from mechanical damage, I think that the heavy insulative coating also greatly increases the resistance to damage from racing arcs, self-strikes, etc.

There is quite a bit of "technique" required to get the perfect mirror surface finish, but much experimentation has shown that the use of a 3-4" wide "foam" paintbrush yields the best spreading of the resin and yields the best finish.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob