[TCML] High voltage input snap when adjusting unloaded Terry
huil888 at surfside.net
Tue Dec 11 23:27:21 MST 2007
I have a Fritz R-C filter on my 15kV/120ma powered 6" X 30" coil, and I have
experienced something similar to the input side arcing you noticed. My
filter is actually a modification of the original Fritz design. I have a
3-ball safety gap on both the input and output sides of the filter, using
3/4" diameter balls. The R-C filter uses (2) 1k ohm, 100 watt wire-wound
resistors, (2) 500pF ceramic bypass caps, and I don't use any MOV strings.
During operation and especially during tuning, as the input voltage was
ramped up via variac, I occassionally got flashovers at the output side
ball gaps. However, under some operating conditions I've also seen
flashovers at the input side safety gaps (NST side). I've never seen both
sides arcing simultaneously. Lead length from the NSTs to the input side of
the filter is about 18", and lead length from the output side of the filter
to the static spark gap is about 30". As the coil was gradually brought into
optimum tune, flashovers at both spark gaps was almost completely
eliminated. The flashovers at the input side were disconcerting, but both
60ma NSTs (very old General Electric high power factor units) are still
alive years later.
----- Original Message -----
From: "Jim Mora" <jmora at jetlink.net>
To: "'Tesla Coil Mailing List'" <tesla at pupman.com>
Sent: Sunday, December 09, 2007 1:55 PM
Subject: [TCML] High voltage input snap when adjusting unloaded Terry saftey
> I was adjusting safety gap for my used Terry filter. This will be for 4"
> demo coil which has a block diagram what stuff is and the wire path.
> Independent of that, I was setting my safety gaps to fire at 140v
> in, on the bench. Wow, just before the safeties fire, I get a 2" hot snap
> accross the filter input. It is a very dry out and that stress has to be
> seen across the outputs of my 12KV, 30+ma repotted neon. They safties
> firing immediately afterwards. I closed them a bit, about right, and it
> still happens unless I ramp the voltage up very slowly. Is this a reverse
> resonance rise and a discharge of the filter caps? I should mention that I
> need to shunt some transorbs as they are set up for a 15KV PSU. I'm Glad
> tranny is still working!
> Has anyone else ever seen this happen with the classic filter?
> Jim Mora
> Tesla mailing list
> Tesla at www.pupman.com
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