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Re: the back of secondary winding



Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>

Nick -

The toasted single turn is very strong evidence that this one turn was shorted. It could have been shorted from the beginning, or it became effectively shorted after some period of operation when arcing and carbonization occurred between two adjacent turns under the fiberglass. It's probable this occurred where the wire's insulation had been accidentally contacted by your angle grinder.

I sometimes need to "touch up" the OD of my epoxy-coated secondaries to remove minor imperfections if a dust mote has settled on the form while the epoxy was curing, but I only hand-wet-sand using #400 or #600 grit silicon carbide paper, not an angle grinder!

Did the coil's output decrease after it ran normally for a while, or were you doing real-time tuning so the first thing you noticed was the arcing/flame at the shorted turn?

As for the earlier arcing in the interior of the secondary, I assume that no baffles were installed?

Regards,
Scott
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Tuesday, June 27, 2006 10:35 AM
Subject: Re: the back of secondary winding


Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>

Hi Scott,
It was my secondary. The fiberglass is 3 layers of fiber decking (woven) cloth, with polyester resin. The wire is 200 deg. Essex formvar covered 18 guage magnet wire from Whitmor wire, close wound.

I cut open the fiberglass to see the pvc underneath was charred badly. the inside of the fiberglass was burned at the failure point of course but the rest was fine, whereas the PVC had a blackened ring from where one turn was so hot it charred all the way around the tube. the magnet wire's insulation was black and crispy for about 10 wraps at that point, but had not actually broken through in any one location.
(SNIP)
but it is possible that there was a part of the magnet wire's insulation sanded off - after the first coat of fiberglass was applied, I wanted to smooth out any bumps and make sure no air pockets made it between the first and second layers but got a bit aggressive with the angle grinder/sanding disc at the first go. This is mostly a theory, but nearby magnet wire to the failed part had some copper showing which tends to support the theory.
> ----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, June 26, 2006 9:00 PM
Subject: Re: the back of secondary winding