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Re: [TCML] Spark gap
Lau, Gary wrote:
Of course the BPS will be different from coil to coil, but I believe the 150-300BPS range would include most coils built to reasonable parameters. My measurements were over, I think, a 1/2 sec interval. Mostly I wanted to emphasize that static gaps will never operate at a constant 120BPS, as many newbies (including myself once) might think.
Ok, I understand. I agree.
I can say with certainty that when I used .02uF and the static gap, it charged to >20kV (what the static gap was always set to) in far less than 18ms. I don't know that I had measured the BPS with the storage scope at that point, but I'm certain it was a great deal more than 55 BPS. And when I tried using a .03uF cap, the gap was still set to at least 20kV, and while it ran rough, it surely fired more than at 2BPS! I think your analysis fails to take into account the super-charging that occurs due to ferro-resonance.
Yes, the cap had to charge to it's setting by the gap in order to fire.
I know the time frames for charging are large. This is likely due to the
charge dynamics, but also probably due to the gap heat and environment
during running. The transformer is either finding current somewhere else
or the gap is firing at a lower voltage on average. That's the only way
bps is going to increase, and I'm not saying it doesn't increase, I'm
simply saying one or both of those things is occurring.
However, you say larger cap sizes allow a larger bang size. In general,
yes, but not always. Your 15/60 you might calc at 12 joules if you
didn't consider the voltage at the cap at each firing of the RSG at
120bps. Energy drops down to 3.92j! The .02uF cap is up at 4.03j. So,
this is part of my problem. To state there's a higher bang energy is not
correct (and I've heard that stated many times but without any data to
support it). I think the larger cap size performing well is for another
reason such as arc dynamics and transfer functions.
With my static gap, I left the gap the same, so increasing the cap size would always directly increase the bang size.
Yes, I understand that in a static gap. This results in a slower charge
time and lower bps and higher bang energy (static gap). Eventually, bps
will get ridiculously low and presto, use an SRSG because it does allow
a larger cap up to a point.
When I made the move from static to SRSG, I experimented with cap size to see which resulted in the largest bang size with the 120BPS SRSG. Unlike in the case of the static gap, the bang voltage now varies with cap size, so here it IS correct to say that a larger cap size will not necessarily result in a larger bang size. Here is the table of measurements, showing cap size vs. Vbang and bang size:
.02uF 24.4kV 5.95J
.03uF 21.9kV 7.19J
.04uF 19.6kV 7.68J <- Biggest bang size!
.05uF 17.1kV 7.31J
Energy is higher than I would calc, but that's ok. As the cap was
increased in size, current took longer to charge and voltage drops. Bang
energy increases and then starts to go down. Your 15/60 appears
equivalent to a 112mA output. Regardless, you've shown what I've been
trying to say. The only thing that has changed is the current is higher
which alters the crest point. For your test, that crest point was .04uF.
I understand that you are talking in generalizations regarding common
coils and in most cases a larger cap would increase spark length. The
only reason I "injected" into the thread is there are qualifications to
everything. I understand why an RSG allows a larger cap and know there
is a crest point. That point is different for different systems. So that
was my basic point.
Take care,
Bart
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