[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
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