POLE PIG TESTING
Subject: POLE PIG TESTING
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Sun, 16 Apr 1995 04:43:00 GMT
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Quoting Ed Sonderman:
ES> Yes my new variac is a Powerstat Variable Autotransformer.
ES> 240v in 0 - 280v out 28A 7.8KVA.
ES> Well, last night I spent about 5 hours testing with the new
ES> pole pig. I have the welder in series with the line side of
ES> the variac. The output of the variac goes directly to the
ES> pole pig. This is a completely different animal. If I did
ES> not know better, I would think this is someone elses'
ES> project. Everything is different and confusing. If I would
ES> have had your home phone number last night I would have
ES> called you. I think I have taken about five steps backwards
ES> and two forward.
Yes, well, ummm. Pole pig coils are a bit of a different animal,
but you can be assured that when you finally get the hang of it
that you won't look back. The other thing is is that you don't
have to worry about a kickback hurting the pig.
ES> Durring all this testing, I am monitoring the primary
ES> current into the pole pig and the primary voltage. I am
ES> still running on my only home made rolled capacitor so I
ES> want to keep the pole pig input under 150 to 166 volts
ES> (should be 9 to 10kv out).
ES> The first big difference that I found is in the spark gaps.
Yes. That was the first thing I noticed when I made the switch.
If you had been observing closely you would have noticed the arc
color at the gap whiten considerably when the power supply switch
was made. There is a lot more current at the gap. Neons and pole
pigs are different breeds of power supply.
ES> When I used to use the neon transformers (12kv -at- 120ma -
ES> controlled to 9 to 10kv max) I used one cylindrical
ES> spark gap and it would fire at about 5 to 6kv. Now I slowly
ES> increase the variac up to 150 to 160 volts and the spark gap
ES> will not fire. I tried two gaps in parallel and they will
ES> just barely fire. Finally I used one gap electrically
ES> folded in half and it will fire at about 130 volts - should
ES> be about 8kv - but when it's running, it sounds like
ES> it's tearing the hell out of the gaps.
It probably is tearing these gaps up a bit.
ES> These gaps are 7 2.0" dia copper pipe sections about 2.5"
ES> long and gapped at about .030". Then I tried both gaps in
ES> series each folded in half. Now it just barely fires at
ES> about 10kv. Then I tried both gaps folded in half and in
ES> parallel. This doesn't work very well. They won't
ES> consistently fire together. It seems to go back and forth,
ES> first one then the other will fire. I finally ended up just
ES> running one gap folded in half.
This gap design is good, but it cannot quench this kind of power.
ES> I suspect I am now getting a lot more current into the
ES> primary of the coil now but less voltage. You are correct,
ES> this pole pig is very difficult to control. The variac acts
ES> like an on/off switch only. I can control the voltage up
ES> until the spark gaps fire then I have no control. As I ramp
ES> up the variac, the voltage on the pole pig primary goes up
ES> to about 130 - 140 volts, current is only a few amps at this
ES> point, then the spark gap fires, current jumps up to 25 to
ES> 30 amps and the primary voltage drops down to 80 to 90
ES> volts. This should be only about 5KV out of the secondary.
ES> If I turn the variac up higher, it seems like the current
ES> goes up a bit but the voltage across the primary actually
ES> goes down. What it seems like is I have control of the
ES> current but not the voltage. How do I get the primary
ES> voltage up to say 150 while holding the current to 20 to 30
ES> amps??? I tried a 2000w resistive load and got weak sparks
ES> and only 6 or 7 amps in the primary. I finally switched
ES> dischargers - back to my original 14" toroid. I get a fine
ES> fireworks display. Many violet discharges about three feet
ES> long. A good display. The primary voltage is still only 80
ES> or 90 volts.
Very good description of the problem.
ES> I think I finally have a setup similar to yours - without
ES> the rotary gap. How do you ever get the primary voltage up?
ES> Do I need to add resistive loading in parallel with the
ES> welder? You said it is possible to eventually eliminate the
ES> welder, which is good, we will need it back at work some
ES> day. I think if I had the variac, the pole pig and the
ES> line hooked up with no load, the current would go through
ES> the roof.
The problem here is with your spark gaps. They are not designed
and constructed to handle the high current output of the pole
pig. Once the gap fires, the arc is so thick and hot that the gap
is not able to "quench" it. Without a gap that quenches, the
power from the pole pig shifts from the tank circuit and into a
short circuit across the gap. This explains the growl, high
current draw, and reduction of secondary spark.
The cylinder static is a passively quenching gap. A series of
short gaps, electrodes that act as heatsinks, and mild airflow
in a compact unit works quite well with moderately powered coils
supplied with neon sign transformers. As you are finding out,
this design falls short when you throw externally ballasted
transformers across it.
The first suggestion I would make would be to balce the capacitor
across the HV line, and move the gap in series with the primary
coil. That may help some.
The next suggestion is to construct an actively quenched gap.
This does not mean you have to go out and build a rotary right
away, but you do need something with a high speed airstream, or
tight magnetic field, in between at least one gap electrode to
actively disrupt the arc.
Your photos shows a beautifully made safety gap. A single gap
constructed like this, but heavier duty, with a focused air blast
from a vacuum cleaner motor aimed into the center of the gap
would go a long way about now. This is just a suggestion in an
area that certainly is wide open to good ideas.
... If all else fails... Throw another megavolt across it!
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