RE: flashover

To: tesla-at-pupman-dot-com
Subject: RE: flashover
From: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 25 May 2000 16:46:13 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

I once had problems similar to what you describe.  They began when I tried
using large air-core RF chokes in my NST protection circuit.  It seems that
some resonance developed in them and it raised my entire tank circuit to
un-godly potentials that would arc to anything remotely near by.  I tried
series damping resistors and mounting the chokes off-axis to the pri and sec
coils but nothing helped.  I now know better than to use chokes at all, in
favor of R-C protection networks.

Another possibility is if your main gap is set too wide, although 3" arcs
are hard to imagine.  Is that 3" of air or along some "insulating" surface?

Regards, Gary Lau
Waltham, MA USA

-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, May 25, 2000 1:21 PM
To: tesla-at-pupman-dot-com
Subject: flashover


Original Poster: "A W" <fateagk-at-home-dot-com> 

I am still trying to get my first coil together. I have been plagued
with flashover arcs from my primary to the secondary. I am using a
7.5kv/30ma NST, saltwater bottle caps with total of .013uf, a single
static gap(2 brass bolts), and a 4" PVC secondary wound 21" with #24
magnet wire. I originally had a 14 turn primary of 1/4" refrigeration
tubing in a flat spiral. It had 1/4" spacings and had an inner turn
diameter of 7". It arced so bad that it seemed to turn the distance
between the primary and secondary into a 1.5" gap. I put a section of 6"
PVC between them, changed the coupling, wrapped both in electrical tape,
covered the first turns of the primary in clear tubing, tried different
tapping points on the primary, all to no avail! I scrapped the 1/4"
refrigeration tubing primary and have made a new primary. I made a 11.5"
diameter helix spiral primary using 12ga wire. Remember, my secondary is
4" diameter PVC. It is now arcing over 3" to get to the secondary. I
cannot make it stop. I am using the same 7.5/30 NST. I have checked the
entire circuit and cannot find anything that looks fundamentally wrong,
so why is this happening. I have tried it both with the RF ground on the
secondary, and without. I have wrapped the bottom half of the secondary
in electrical tape, and placed a section of 6" diameter PVC around the
primary. It has now burned the PVC, smoke was everywhere! I have been
checking tons of websites on the internet and I have yet to see an
instance where the primary requires more than three times the diameter
of the secondary. Could it be my transformer? I am getting to frustrated
with this! HELP!

Thanks,
Andrew