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Re: the back of secondary winding
Original poster: Billy Watson <Aesops.Tech@xxxxxxxxxxx>
The boy's and I made a spark gap Tesla coil at work to play around
with on our breaks.
We wound the primary on a two foot piece of fiberglass pipe
insulation about 14" wide.
it was somehow absorbing the RF current, and we could not get any
output from the secondary. We rewound it on a cardboard form, OK then.
The secondary was 1000' of #14 THHN. I think the primary was 4 or 5
turns # 10 THHN.
The spark gap was HeliArc welding electrodes, in brass holders.
Cap was a 3' X 3' X 3/8" tempered glass. 15 Kv 60 Ma ignition trans.
when tuning it up, the boys thought I was crazy, because I kept
putting my hand up to the discharge, but my mussels kept pulling my
hand back. Finally resonance, and I was able to draw about 2' to
21/2' thick beautiful waving arcs to my hand.
We played with that coil for weeks while on breaks. On one occasion,
one of the fellas was holding a florescent tube in his hands, with
the close end about a foot sticking out from his hand, when a bolt
jumped about a foot from the tube end to his chest. scared him.
Another time we had the tube on a stand about a foot from the
sec.electrode, with the other end resting on an iron pipe hand rail,
in the concrete floor,with a foot overlap from the tube end, At the
end of the hand rail , about 4" away was a metal filing cabinet
sitting on the concrete floor. next to that was a metal office chair
with 5 rubber wheels.
The arcs jumped the one foot gap to the end of the fluorescent tube,
lite it up, jumped out the other end of the tube, wrapped around it,
and jumped to the hand rail, jumped a beautiful
thick arc the 4" to the cabinet, Jumped about 6" to the chair, and
jumped around all 5 wheels to the floor. All the while the arcs were
pulsating and flowing with the air currents, and were thick bluish white.
We would store the parts in separate places in the shop so the boss's
wouldn't know what it was. one nite while putting the plate glass
cap. away, it slipped out of my hands about an inch from the floor
and shattered into little 1/4" pieses but were still held together
somehow , and it released a strong O-Zone odor. especially when shook
while hanging from the hands.
Just a coilers experiences.
Tesla list wrote:
Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>
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.
This PVC core has failed once before but the last time it was from
internal arcing. the inside had since been sanded and covered in
fiberglass and this time the inside was fine. so I am fairly certain
the pvc and fiberglass are good materials in general, 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.
Also, I must correct Aaron slightly- when I first fired this coil
up, the arcs were quite a bit larger than I had previously expected
(partly due to his help :)). Also, the primary was a bit overcoupled
and some of the initial arcs were from the primary to the secondary.
I immediately moved the primary down before any of the later (and
much more impressive) power-up's but apparently the damage had
already been done.
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
Sent: Monday, June 26, 2006 9:00 PM
Subject: Re: the back of secondary winding
Original poster: "Scott Hanson" <huil888@xxxxxxxxxxxx>
" I was watching a friend's coil this weekend, and his secondary
suffered an interesting yet unfortunate
fate: All of a sudden, a bright spot of light appeared on the
side of the secondary. After turning
off the coil and approaching, it was observed that a nice little
hole had burned in the winding. It did
not appear to have resulted from a strike or racing sparks or
anything quite so obvious."
"His secondary was coated with fiberglass."
When you state that his secondary was coated with "fiberglass",
what exactly do you mean? Fiberglass cloth or matt, impregnated
with polyester or epoxy resin? Or just coated with resin, without
If it was truly covered with fiberglass, was it woven fiberglass
cloth, or random-fiber matt?
If glass was actually used, can you find out how many layers were applied?
Also, can you find out what type of wire was used to wind the
secondary? Conventional enameled magnet wire, or something else?
Close-wound, or space-wound?
Always interested in the conditions leading to a failure, and the
results of the subsequent failure analysis......