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Varnish?

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Spedy

Fri Dec 28 2007, 08:25PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

What do you use to "seal" your secondaries? is sealing necessary? The only thing I could find was some odd goopy stuff that didn;t dry clear and seems more like rubber cement than anything.

Marko

Fri Dec 28 2007, 08:43PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Absolutely, you need to varnish your secondary immediately after winding or windings will unravel and overlap.
Always make sure you have your varnish prepared before you start to wind, I had some bad experiences with that.

The guy who donated me the wire once gave me some of that transformer and motor winding varnish, and I was very pleased with it. It is very dilute and windings drink it nicely. Actually the best varnish I would recommend.

Only drawback is that it solidifies fast in storage, especially if container is continuously opened and closed.

2-component varnish would be much better in this case.

Next is polyurethane spray, also a good thing but can get expensive for larger secondaries.

I also used polyester marine resin, does the job well but is dense and doesn't soak the windings as well alone, but can be diluted by styrene.

I noticed other people use epoxy resins (Americans although seem to call all resins ''epoxy'').

Steve Ward

Fri Dec 28 2007, 08:57PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

I noticed other people use epoxy resins (Americans although seem to call all resins ''epoxy'').

We sure do

.

Epoxies seem to work pretty well, but there are a few things to be careful of. Get a rather "thin" epoxy, something designed for coating furniture is good. Many epoxies designed for mechanical connections are too thick to give a smooth surface when cured.

Be sure the surface of the secondary coil is free of oils! A wipe down with some alcohol should be OK, and make sure the thing is totally dry before coating. I dont suggest blasting it with a heatgun or anything, though, as this could have other bad effects from extreme thermal expansion, so let it dry in natural or maybe slightly warm conditions.

To apply the epoxy i use a piece of plastic or cardboard, about 5" wide with a nice straight edge. The coil needs to be on a rotating fixture. With the coil spinning, i pour on a small blob of epoxy and press the edge of my card against the form to nicely spread the epoxy. Holding the card at the correct angle will make the epoxy naturally advance in one direction. Keep adding small amounts of epoxy as necessary to give the coil a nice thick coat. I usually work fast to give the coil a rough coat, and then work back through it again to smooth it all out nicely. The end result is usually very nice looking and is about 1/16" thick or better. If you notice a bunch of tiny air bubbles, one trick to pop them is to use a hot air gun (or hairdryer on a low setting) to gently heat the surface, making the air bubbles expand and pop. Be sure to do this early enough in the curing process so that the epoxy can re-settle and not be full of little dimples!

I use the epoxy method because i can do it safely indoors, where as polyurethane will stink out the whole house, and takes many coats to get it thick enough to be protective. The only drawback to the epoxy is that you only get 1 chance to make it look nice!

Tom540

Fri Dec 28 2007, 09:05PM

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

I will never go back to using varnish. I use this

which is epoxy for furniture like Steve said. I love it. It's much more durable and better looking than varnish. A little goes a long way as well.

Spedy

Fri Dec 28 2007, 11:54PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Thanks. I ended up using M3's electrical sealant, "for use with vinyl electrical tape". It was a goopy mess and I think I'm going to have to make another secondary. Oh well, at lease my make-shift drill-motor winding jig worked fairly well. I never thought wire could be so springy..

Avi

Sat Dec 29 2007, 03:04AM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

I used several coatings of 'cabots crystal clear' using a foam brush. The secondary must be rotated slowly as it dries (i just used a stepper motor)

Spedy

Sat Dec 29 2007, 08:55PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

So, varnishing is mainly to keep the windings from unraveling? I thought it helped w/ insulation, but ok. So, furniture epoxy? I've never heard of it, but I should be able to get it.

Where can I get it? Lowes? other hardware stores? Or will I have to go out of my way to some specialty shop?
I ask because I've never seen the stuff, but than again I've never looked before.

thedatastream

Sun Dec 30 2007, 08:21PM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

I've had some success with Ronseal Ultra Tough Hardglaze varnish from B+Q (in the UK)

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