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Final Capacitor Test Results
Well, it looks like rwstephens was correct. The 30 ma transformer would not
produce enough current to test the .025 mfd capacitor. I connected the
capacitor directly across the pole pig last night with the rotary gap in
parallel ( and three .030 static gaps in series with the rotary). It fired
very loud and very hot. The pole pig primary current was about 15 amps
(3.6KVA).
Then I reconnected the whole system one component at a time - and everything
worked normally. Now I was puzzled, why did it work now, but not the last
several times I tried this? I ran the system for several minutes off and on,
trying to dial in the best tune on the primary. I had the primary current
set at about 25 amps. Then I noticed that I had forgot to plug in the
resistor bank for the parallel load to the welder. I plugged it in and tried
the system again and it would just barely fire. Primary current dropped to
about 10 amps and the gaps would only just barely sputter. This has
apparently been my problem all along. I don't understand it at all. Adding
resistance in parallel with the welder should increase the primary current.
Last year when I was spending a lot of time on this project, I mentioned to
Richard Quick that this system was very particular about how I had the
primary AC system configured. It would only work well with three 2000 watt
oven elements in parallel with the welder - not one or two or four and not in
series - only with three and only in parallel. He said that I had a
synergistic tuned system where the primary AC feed and the coil primary are
somehow in tune. I guess when I rebuilt the primary by shortening all the
interconnections and replacing all the wire with 3/8" copper tubing, I must
have unbalanced this tuned system. Does this make any sense? Now it runs
very well with just the welder and no extra resistance. I am not sure it
is any better than it was but certainly just as good - still about 74" for
maximum spark length. I was hoping to increase it's performance by doing
this.
Last fall I was having a lot of problems with discharges hitting down into
the primary, past the strike rail. I could only run the system at full power
with a wire or some sharp object on the toroid to direct the discharges away
from the coil. Over the winter, I added a raised ridge all the way around
the top outside edge of my big 40" toroid. I used 3/8" clear plastic tubing
and taped it in place then covered it with foil tape. This has helped a
great deal. Now I can run for sometimes up to 30 or 40 seconds without
getting a strike down into the primary (past the strike rail). When this
happens the safety gaps fire and stay fired shorting the pole pig until I
turn the power off. I have watched Richard Quick's video of his system
running for what seems to be 5 or 10 minutes straight without any problems
like mine. What am I doing wrong or not doing that could prevent this?
Now the big news - so it turns out that Condenser Products was right. The
capacitor was indeed good. Not so any more. I was running at 35 to 40 amps
of primary currrent (about 9KVA) and I was slowing increasing the rotary gap
speed to see its impact on performance when the capacitor exploded. It blew
one end off, breaking the plastic around the area where it was glued, the
glue held. I heard a muffled explosion, saw a flash of light (fire?) and
everything went dead. These things are made up of 5 or 6 (I haven't taken
them all out yet) sections all in series. Each one is just a little less in
diameter than the inside of the case and about three inches long. It looks
like it is wound with very fine foil and thin dielectric. What a hell of a
mess, it puked oil all over everything.
Why did it fail? Too much voltage or just too much total power? This cap
was only rated at 15kv. This is 15kv Tesla coil service. They knew my
supply was a 14,400 volt pole pig. Do I need to order a 20 or 25kv capacitor
next time?
Sorry this was so long.
Ed Sonderman