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Clear epoxy secondary coating

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Acacia

Tue Sept 27 2011, 06:37AM

Registered Member #4073 Joined: Sun Aug 28 2011, 08:43AM
Location: Australia
Posts: 17

Hello,

I have recently started making my first coil, (Mini SSTC from Steve Wards design) and I'm a bit stuck with coating my secondary.

The coil is somewhere between 900 and 1000 turns, wound onto a white PVC form, 42mm diameter by 166mm of total coil length.
I have read as many previous threads as i could find on the subject here, and I want to use clear epoxy to coat the coil. I have been into a few hardware shops and had a bit of a look around, and the only clear epoxy they have is in the syringes (14mL), and is supposed to dry in 5 minutes. Is this the stuff I need, or do i need to use other epoxys that dry slower? Also, would one or two of the small syringes be enough to coat the entire coil?

I want to finish the coil as soon as possible, and i dont want to do several coats.
Thanks, Nic.

ZakWolf

Tue Sept 27 2011, 02:31PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I never thought to coat a coil in epoxy, i think its a little to think to be moving it around smoothly. I went to the store and grabbed a small can of high gloss varnish. i put two coats on like 15-20 min apart of each other and then waited about 2 hours good to go, it was thick enough to where you could see the layer.

Kizmo

Tue Sept 27 2011, 02:52PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

This is my big drsstc secondary (315mm dia 1350mm long wound with 0.71mm wire) which i coated with epoxy. Single shot coating, no sanding or other work, just mixed almost 1000g patch at once and applied it on motorized winding jig with good quality brush.

It turned out to be really nice thich coat with almost no imperfections :)

Epoxy is the way i will coat my coils in future! No more solvent fumes and multiple coats.

Type of epoxy used was this:

It is sort of expensive but in future i will find out if normal boat epoxy with solvent could be used :)

Matt Edwards

Tue Sept 27 2011, 03:01PM

Registered Member #2838 Joined: Fri Apr 30 2010, 07:55PM
Location: tehachapi, CA
Posts: 333

I've said this before and I'll say it again..

Keep it rotating until it is dry, use an hot air gun directly after it is applied to remove air bubbles.

You will be vary happy with the results. One $20 box is easily enough for 2-3 (3-4") secondaries.

Herr Zapp

Tue Sept 27 2011, 07:21PM

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

Acacia -

You want to use a commercial clear epoxy coating resin with a "pot-life" of at least 1/2 hour. 5 minute epoxt would start to gell before you even began to get it applied to the coil.

I've applied epoxy coatings to secondary coils for years with uniformly excellent results. When done carefully, a single application of epoxy creates a thick coating that ends up looking like the secondary is encased in a glass sleeve.

Here's a link to the detailed application instructions:

Herr Zapp

]procedure_for_epoxy_coating_secondary_coils.pdf[/ file]

Acacia

Tue Sept 27 2011, 11:34PM

Registered Member #4073 Joined: Sun Aug 28 2011, 08:43AM
Location: Australia
Posts: 17

Ok, thanks for the responses. I will go and have a look around for these products or their equivalents. I just finished the control and power circuitry for the coil, so it shouldn't be too far away from being powered up, if i can coat this secondary today or tomorrow.

Thanks, Nic

lightlinked

Wed Sept 28 2011, 01:34AM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

i use finish epoxy from the local hobby shop. it's by bob smith industries and supports a local business. you can also get finish and slow cure epoxy at serious hardware stores, plastic supply places or if you want to spend too much, boat stores. thining it with denatured alcohol can help it flow better and the cure time will be longer. just keep it turning as it cures. I found it to be much less of a hassle than varnish which has to have each layer sanded or it will delaminate the coats of varnish. since there will be quite a bit of epoxy surface area you should wear a organic vapor respirator

Herr Zapp

Wed Sept 28 2011, 02:18AM

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

Acacia -

Don't even think about trying to epoxy coat a secondary without a variable-speed winding/coating jig to rotate the coilform during application and curing of the epoxy.

You'll want a speed range of around 10-30 RPM, depending on the coilform diameter.

A crude setup can be built using a variable-speed drill, or a nicer version using a DC motor driven right-angle speed-reducer.

Don't try to "rush" the job, or you'll end up with a disaster. You might want to try applying epoxy to a small section of bare PVC pipe first, to get a feel for the application process.

Herr Zapp

Acacia

Thu Sept 29 2011, 09:01AM

Registered Member #4073 Joined: Sun Aug 28 2011, 08:43AM
Location: Australia
Posts: 17

Herr Zapp, I have rigged up a variable speed drill to turn the coil at the right speed, so this is'nt a problem. I have also read how you coat your secondaries, and I plan on doing something very similar.

I havn't been able to find clear epoxy with apropriate drying times yet, but they do have polyurethane casting resin. I was wondering if this would be suitable, it is labelled to be crystal clear when cured, and has a cure time of 24 hours. The resin also shrinks when curing and generates heat, could this be a problem?

If this polyurethane casting resin isn't suitable, I can have more of a look around other hardware shops, as well as paint shops and hobby shops.

Thanks, Nic

Herr Zapp

Thu Sept 29 2011, 10:04PM

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

Acacia -

Never heard of polyurethane casting resin, are you sure it's not polyester? Any kind of casting resin may not be the best choice, as that is usually optimized to cure properly in thick sections, whereas "coating" or laminating resins are optimized for use in thin sections or coatings. Try hobby suppliers and specialty woodworking stores, as epoxy resins are frequently used for coating wooden tabletops, bar tops, counters, etc. Also check out marine supply stores, as epoxy resins are now being widely used in laminated fiberglass boat hulls.

Or, just google "clear epoxy coatings", there's got to be multiple suppliers down there.

Herr Zapp

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