Subject: PROJECT UPDATE
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Mon, 24 Apr 1995 23:53:00 GMT
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* Original msg to: Esondrmn-at-aol-dot-com
Quoting Ed Sonderman:
ES> I thought I'd let you know what's been happening. I built a
ES> spark gap similar to the one I saw in your video. With five
ES> 1.5" copper pipe sections set up with my shop vac to draw
ES> air down between them. I held them in place clamped from
ES> the ends with several layers of .0625 polyethylene. It did
ES> not work very well. A couple of the gaps worked correctly
ES> but two of them arced at the ends only and burned a carbon
ES> trail in the poly.
Yeah, these gaps can be a real witch to set up and run properly.
In order to get a smooth and reliable operation I had to use
plate glass strips to bracket the top and bottom of the
electrodes. This worked for awhile, but required extremely close
tolerances in the electrode construction. I ended up placing
asbestos pads on top of the glass strips to take up a little slop
in the construction tolerances: two rectangular pads per
electrode, one on either end. The pads are set so that there is a
small open space at the top and bottom of each gap. This way the
top and bottom of the electrodes where the arc may hang are not
in contact with any material at all, there is about 1/8th of an
inch between the top and bottom of each gap and the glass
It took me about three weeks of trial and error to develop a
system of electrode mounting that did not burn, crack, melt, or
break down. The trick is to use a high temp padding on glass
plates, and do not allow contact with any material directly above
or below the actual gap. Asbestos is listed as a hazardous
substance, but I have seen batting and padding made of 100%
fiberglass that would definitely work.
BTW, after running a bit with glass compression plates and
separate high temp pads sandwiching each electrode, you will see
why the other designs fail. The gaps produce hot copper ions
and a conductive film is sublimed that will short across the top
and bottom of each gap unless an open airspace is provided.
ES> Then I built a single gap and tried using my shop vac in
ES> reverse to provide an air stream to quench the gap. This
ES> worked sort of. Loud, but the coil did not perform as well
ES> as it has been with the cylindrical gap.
The air stream must have some physical force to it. The air
stream must be focused as tightly as practical, and blown
directly into the gap. The entire output of the shop vac should
be choked down to no more than a 1" diameter at the nozzle,
preferably the entire output should focused from a nozzle no
larger in diameter than the gap is wide. While this may not seem
efficient, a special manifold or multiple nozzles could be built
allowing for mutiple port injection into the gap. Say one nozzle
from below, two nozzles facing off from each side, leaving the
top open for the ejection of the hot plasma.
ES> In all of these tests, I am still not able to get the
ES> primary to the pole pig above 125 volts. I am going on the
ES> assumption that this is still due to inadequate quenching of
ES> the gaps and I am essentially shorting the HV outputs of the
Yeah, that is what's happening.
ES> I now have some resistive load in series with the welder -
ES> about 8000 watts of heaters and oven elements. The primary
ES> current is limited to about 15 amps at this time. The
ES> secondary should be about 7500volts. This should put the
ES> secondary current at about 200 to 250 ma. I am surprised
ES> that my existing gaps can't quench this. It is only about
ES> 1900 watts and I was running at about 1400 watts with my
The pig is a different breed of transformer. The shell wound core
is designed not to saturate at all in normal operation, where the
neon is designed to fully saturate. The output voltage of the
neon drops way off when a high current demand in placed on it;
the core saturates and the field flux is bypassed through the
shunts to choke off the current flow. External current limiting
(on a pig) is not that same as core saturation and bypassing in a
neon. The pig is designed to pass enough energy to acomplish real
work, and the output does not exhibit a voltage drop like a neon
and there is nothing internal to choke off the current flow.
The resistive load is effective to smooth things out and make
things more manageable. I am sure you noticed the resistance took
the nightmare edge off of the system and made life much easier on
the variac(s). But resitive and inductive ballasting do not turn
a pig into a neon. There is just no comparison.
ES> My next project is a rotary gap.
The rotary in series with a static gap will get you straightened
out and will allow you to undo the short circuit across the HV
bushings of the pig. This gap combination will redirect the
energy back into the tank circuit and will allow you to open the
power supply up. By using a quenching static gap in series with a
well designed rotary, the rotary gap can deliver very short dwell
time. In the end it is pretty easy to get a gap system that will
commutate and quench. A properly designed rotary/quencher gap
system on a pig will deliver spark gap performance that you won't
ever see out of a simple static gap on a neon. Of course it does
take time to put it all together.
... If all else fails... Throw another megavolt across it!
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