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Re: 120 bps vs. 240 bps comparison tests

In a message dated 99-05-31 18:09:35 EDT, you write:

<< 
> Reflecting on the proposed experiment shows how difficult it can be 
> to keep things in separate compartments. If one is to keep BPS 
> constant and Vp constant, the charging current is going to have to go 
> up with primary cap size which = an increase in input power. Nett 
> result however is that Vo is constant if total secondary capacitance 
> is increased to match (by increasing Ctop) and available charge at the 
>top terminal is increased with the same rep rate. My question here 
> is: do sparks get longer at the same rep rate as a result of 
> increased terminal charge or do they stay the same length and just 
> get hotter? I am curious to see the dependence of sparklength on 
> available terminal charge. I think it's come out in other experiments 
> that there is a sparklength dependence on voltage. I'm making an 
> assumption that the change in gap loss isn't going to make a huge 
> difference.


Hi Malcolm,

Thanks for the futher info.  So if for instance the input power and Cp
is doubled, then Cs (total) will have to double too.  In the case where
I use 570 watts to get the 42" spark using the 4" by 17" toroid, If I
then double the input power to 1140 watts, the required toroid size
to double Cs total would be quite large.  If we assume the original
Cs is 30pF (7pf in coil, 23pf in toroid), then we need 60pF in the 
new high power setup.  I suspect that a 53pF toroid will be 
"too large" for best results, and who knows, it might really crimp
the spark output and limit it to 42".  In any case, it would probably
need a break out point to permit breakout, unless it has a 
relatively small minor diameter.

I could probably start with a 3" by 10" toroid, at 0.0077uF
for Cp, at a certain input power that gives one streamer at 120bps,
then install the 0.0147uF cap, and ~double the input power, and
verify same Vp on scope,  and use the 6" by 26" toroid (which 
hopefully might give a doubling of Cs), and see what kind of 
spark length I obtain.  Let me know if you see any problems
with this proposed test, or can recommend any improvements
in the test approach.

Thanks,
John Freau

 
> A suggested approach then is to start out with a gap firing voltage 
> that doesn't change, a relatively small Cp and small Cs, and measure 
> peak length. Then up Cp and Cs so tune is maintained and adjust 
> charge current so that BPS remains constant.
 
>     The point: it is obvious there is a sparklength dependence on 
> input power for a given coil but I'm interested in seeing what effect 
> the voltage and current have individually. Knowing things like this 
> would help explain why some coils do far better than others and 
> should point the way to better designs given available components 
> and/or power supply.    
 
> Regards,
> Malcolm
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