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Ruined secondary? HELP!

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Hart

Sat Dec 27 2008, 03:19PM

Registered Member #1885 Joined: Sat Dec 27 2008, 03:04PM
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Posts: 3

While coating my latest secondary with second layer of poly varnish something strange happened while it was curing. There was few hundred BIG bubbles (approx 4mm in diameter) sitting around the secondary. When it was completely hardened i sanded and cutted them away very carefully with razor. Everything looked good until i started cleaning out dust and varnish particles with vacuun cleaner and viped it with acetone. I sanded as carefully as i ever could but still it seems that i managed to sand completely through varnish and wire coating. There are now several places where shiny copper is more or less visible. Wire itself is ok (no metal removed). I have now applied about 5 coats without porblems after that but im very worried if i ruined it.

Seriously words cannot express how angry and disappointed im right now. I dont have money to make new secondary that size (it is 10" coil)

vasil

Sat Dec 27 2008, 03:30PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Breakdown appears mainly because the irregularity of the electric field at the surface of the secondary (bumps, overlaped turns, etc). If the surface is flat, even if the copper metal is exposed I think that it would not be a problem. Just apply suficient varnish and keep a good air clearence between sec and primary.

Hart

Sat Dec 27 2008, 03:36PM

Registered Member #1885 Joined: Sat Dec 27 2008, 03:04PM
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Posts: 3

I think i will do like Dr. Spark did with his Fatboy and hope for best

Dr. Spark wrote ...

Get a good base of 20 coats. This will ensure you do not sand into the wire. Then sand lighly with 320-grit sandpaper. Apply three coats and let dry for a few days until you can stick your fingernail into paint with no mark. Sand with 400-grit sandpaper, apply three to five coats, and let dry a week. Then the fun with Wet/DRY Black sandpaper. Put a little water on coil and sand your brains out. Apply three to five coats and sand again with 800-grit WET/DRY Black sandpaper. Let dry a week, say your prays and apply last coat."

I feel really bad

Maybe couple beers help

Dr. Dark Current

Sat Dec 27 2008, 06:02PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

What matters is that the isulation right between the turns has been left intact. If you sanded the varnish just off the "tops" of the turns, putting on a few coats of varnish will fix it 100%. I think that even when would you left it like you have it now, there won't be any problems with spark-overs or shorted turns.

Hart

Sat Dec 27 2008, 06:15PM

Registered Member #1885 Joined: Sat Dec 27 2008, 03:04PM
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Posts: 3

Only "tops" of the turns here and there are exposed. Wire is double enamaled and there is nothing wrong with between turns.

NickCesar

Sat Dec 27 2008, 11:50PM

Registered Member #1799 Joined: Thu Nov 06 2008, 02:20AM
Location:
Posts: 23

How bad are overlapped turns? I was getting tired towards the end and turned the lathe speed up a little. I have a few overlapped turns near the bottom of the coil. Obviously it isn't good, but how big of a deal is it? It's a twin coil setup and according to JavaTC has an output voltage of 555kV with a 21kV spark gap breakdown voltage. Since my primaries are in series each coil is only doing ~275kV divide by 1000, there's only a potential of 275V between turns.

teslacoolguy

Sat Dec 27 2008, 11:52PM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
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Posts: 792

If you make the end with the overlapped turns the bottom of the secondary (connected to ground) then you "shouldn't" have any problems.

Kizmo

Sun Dec 28 2008, 11:41PM

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

Does someone have experience with tiny bubbles in varnish?

I just got my large (40cm x 200cm) secondary coated and there is load of tiny bubbles trapped inside the varnish. Mostly they are located between turns here and there. I managed to make 20 buble free coats after that first one which has thos bubbles in it. Hope it does because its more expensive than my car :)

You wouldnt believe how bad it looked before i reached that 20th coat and sanded it smooth (lots of drips and runs and craters from large bubbles)

NickCesar

Mon Dec 29 2008, 02:14AM

Registered Member #1799 Joined: Thu Nov 06 2008, 02:20AM
Location:
Posts: 23

I could see that causing a problem with "racing sparks", but I have no experience

aonomus

Mon Dec 29 2008, 02:32AM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Nice winding rig Kizmo.

As for sanding through the varnish and insulation, I've done that to my secondary and ramped it up to full power with no ill effect. I have however added many many more layers of varnish to get better insulation.

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