Original poster: Just Justin <rocketfuel@xxxxxxxxxxxxx>
Greetings,
After a long period of research, I've finally started building my
first coil. I must say, I was inspired by Malcolm's speed and so
I've set my sights on having something to show my friends on New
Year's Eve. It will go well with the fireworks and flamethrowers.
Anyway, my first source of good information was Richie Burnett's
wonderful site, which made me want to go straight for a DC
resonant system right away. After thinking it over, I decided
that going DC resonant with my 12KV NST would require a very
high voltage tank cap and that I'd be better off using MOTs due
to their lower voltages. In the meantime, I thought I'd try a
NST-bridge-filter caps DC system. I built a propeller gap but
have had some alignment issues due to the way I constructed the
rotor, so I've shelved that and made a 6-segment (1"x6") copper
tube fan-blown gap. Now if you're still reading I'm sure you're
probably going to say that there's no point in DC with the static
gap and I'm mostly convinced myself.
However, when constructing the fan blown gap, I observed it as
NST + bridge, and again as NST + bridge + filter caps and saw very
different sparks. Without the filter caps, the gap frequency was
very high, and the sparks were purple-orange, and they seemed to
persist as the fan blew them to the far side of the pipe. With
the filter caps (0.1 uF) in place, the gap fired much less frequently
and the sparks were white and seemed "hotter".
Of course this had me scratching my head. My current theory is that
with AC and a static gap, the gap might break down several times during
the portion of the AC wave that is of a higher voltage than the gap
can withstand before breaking down. With the NST + bridge only, this
would be more or less the same situation, but without the reversing polarity.
With the addition of the filter caps though, I imagine that the filter
caps take a wee bit of time to 'fill' to the threshold voltage of the
gap, and when they do discharge, they add to the NST's current, leaving the
cap's voltage after the spark somewhere between 0 and the gap
threshold voltage.
Once the plasma has been created, resistance goes down and so I'd imagine
they are somewhat depleted after the spark. Then the cycle repeats.
I guess the question is how long does it take the filter caps to charge
to the gap voltage and is that longer than 1/120th of a second?
My assumption is that any energy I might be storing in the filter caps
is just going to drain out through the spark gap, and therefore is
pretty much useless without the accompanying charging reactor and D-Q
diode of a full DC resonant charging system. I still don't entirely
understand why the filter caps would not discharge through the spark
gap in a resonant system, except that possibly the charging reactor
limits the current out of the filter caps.
I have a few specific questions that I'll post in seperate emails.
Thanks for reading and I'll appreciate any comments y'all might have
to offer.
Justin in Austin