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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