Re: Thoughts on spark length and the "Freau Equation"

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 6/10/01 8:16:41 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes:

> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
<jimlux-at-
> earthlink-dot-net>
>  
>  I would assume that the equation proposed by John Freau for predicting max
>  spark length  (=1.7 *sqrt(VA)) is based on 120 pulses per second.  That is,
>  it's really more of  (length in inches)= 1.7 * sqrt(120 * energy per bang) 
=
>  18.6*sqrt(energy per bang in Joules).
>  
>  Obviously, there are breakrate effects on spark length, but, for rates in
>  the 100-200 bps range....
>  
>  Comments?

Jim, all,

I agree, and I've addressed this issue in some previous work.  
The equation you refered to above is my original equation, I've
since made a revised equation, using various roots to try to
compensate some for the breakrate.  I'm not 100% satisfied
with the results, so I usually just mention the original equation
for simplicity.  The newer equation is:

SL (inches) = [(3.9*16th rt power)*sqrt power)] / 4th rt BPS

   (for 120 to 480 bps)  

For those without special calculators, 
you can press the sqrt root key 4 times to obtain the 16th rt,
and press the sqrt root key twice to obtain the 4th root on
a normal cheap calculator.  Certain other roots may work a
little better in the equation, but I used those roots for the
ease of working with a normal calculator.  

Regarding the original equation, some coils can do a little
better, so then I use 1.8* or 1.9*, or possibly 2*sqrt input power.

It is interesting though that the original equation works well both
for Richard Hull's Nemesis TC (15' sparks) which ran at 500 bps, 
(possibly a true 350 bps), and for Kevin Eldredge's Biggg coil
24' sparks) which runs at 120 bps.  Kevin may be getting quite
a bit of loss in his ballast though, so it may be capable of
better efficiency.

Cheers,
John Freau