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Re: Medusa's back up!
Tanks for your inquiry regarding Medusa. She is powered by a 10 kVA,
14440/240 volt pole pig. The pig is ballasted by a Linclon 225 Amp Arc
Welder's 240v input winding in series w/ the pig's 240v (input) winding,
and the welder's output leads are shorted. The welder is between the pig
and the voltage control variac. I usually keep the welder's current select
knob set -at- 150 or 175 amps. With this setup, the system draws 8 to 10
kVA (panel meters read 200 to 220 volts and 40 to 45 amps. I could push
it a little higher, but I believe this is just about all that the system can
dle without danger of meltdown! Actually, even -at- 6 or 7 kVA I get about
the same sized sparks in my cramped shop, just less frequent strikes
and not quite as bright.
The new sec. is very close to the old one both in length (39 1/2" vs 41")
and in the # of windings (690 vs 684), so the (L) has changed very little
(probably less than 5 mH). I figured around 35 mH for the old one, ac-
cording to the Wheeler eq, so probably less than 40 mH for the new one.
With the (L) this close, I didn't even need to retune.
The pri. cap is a High Energy unit comprised of (12) iden. 27.5 nF, 42 kV
pulse caps in one 3"x5"x25" long epoxy case w/ heavy term. connections
(18 total). I externally bussed these connections for 2 strings of 6 paral-
leled caps for a total value of 82.5 nF -at- 84 kV. This is a robust unit that
virtually never externally heats up beyond ambient temp. I ordered this
unit from a fellow coiler in Mass. for less than $100, incl shipping. I con-
tacted High Energy regarding this particular cap, and found out that it
would now cost over $1500 to have it made! It was manufactered in 1984.
I'm not sure if you have my coil mistaken w/ someone else's. I have not
posted any pics of it on the web, as of yet. I have snail mailed a few vi-
deos to some fellow coilers (maybe you saw it that way?) On the video,
it was still powered by (2) 1kVA, 7200v pot xfmrs. These required no ex-
ternal ballasting, besides the voltage control variac. This setup did over-
drive the PTs by a factor of up to 5x their nameplate rating (10 kVA).
However, I never noticed any ill-effects with these beasts though. One
interesting observation I did note upon changeover to the pole pig is that
even w/ less power draw, acccording to the panel meters, the system
spewed out more frequent longer, louder, and brighter sparks. With the
PTs, I would draw 200v-at- 50 amps and get only rare sparks that exceed-
ed 8 ft. However, with the pig, with 200 to 220v-at- 40 amps, I get consis-
tant 8 to 10 ft. sparks.
I hope that I addressed your questions to your satisfaction.
Keep on Sparkin'