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Re: Test: Bigger Secondary gives Bigger Sparks
Hi John, all,
John, thanks for continuing to send the results of your
tests. I have been following them with great interest and may be now
in a position to add some contribution of my my own very shortly. To
explain: I was urged to fire a coil for someone last weekend and
although I didn't get around to it then, I am planning to this weekend.
Anyhow, last night, I went through my notes and put a coil together
on paper from the various secondarie, transformers etc. that I have
lying around. What dropped out of the equations blew my socks off:
> Original Poster: FutureT-at-aol-dot-com
>
> All,
>
> Recently I posted my results from a small TC with a 3" by 12"
> secondary which gave 14" sparks using a 7.5kV, 30ma NST,
> 120bps sync rotary gap, 13.3nF cap, and 3" x 10" toroid. The
> #12 wire primary was tapped at 6.5 turns. A nice mini-TC.
>
> I removed the small secondary and installed a larger 4.2" by 23"
> secondary also wound with #28 wire. I retuned at 18 turns on the
> primary as needed. All else remained the same, but the spark
> increased to 22" for a 57% increase.
>
> Other things that automatically changed; greater primary inductance
> and surge impedance, greater secondary inductance and Cself, lower
> frequency, no racing sparks. It is not known how much each factor
> contributes to the 57% spark length improvement.
>
> It is intriquing to consider that perhaps the spark lengths of many
> other TC's could be easily but greatly improved, simply by installing
> a larger secondary with greater inductance, and retuning as needed.
>
> Cheers,
> John Freau
This was all off the cuff and designed using existing components:
1x 15kV 60mA transformer
2x 25nF pulse caps in series to give 12.5nF (roughly 50Hz resonant
with the NST)
1x secondary 6.5" HDPE closewound with 0.9mm wire to give about
850 turns over 32" length
Ls about 20.5mH
The approach: select three terminals I have amongst others and
tabulate Fs, Vo etc. I idly tabulated several different Vp's and plan
to use these with the different terminals, setting the variac to give
100BPS in each case. The voltages were chosen at random. What I
ended up with were three different systems with the following
attributes:
Terminal 4 3 1 (my catalogue)
Fo 250kHz 212kHz 180kHz
Ctot(sec) 19.5pF 27.3pF 37.7pF
Lp (requ) 33uH 45uH 63uH
Xp 51ohms 60ohms 71ohms
Vp (chosen) 15kV 18kV 21kV
Ep 1.4J 2J 2.7J
Again those voltages were chosen by the pen tip. Now for the
cruncher:
Vo (ideal) 379kV 383kV 382kV
Coincidences like that make me think I've gone off the rails
somewhere. Maybe someone else would like to do a sanity check.
Anyway, assuming all is well with the above calculations, it seems I
have an interesting series of tests ahead. Ep, Xp and Cs are the
variables it appears I'll be examining in concert.
Malcolm