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

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Jim,

Wow, couldn't help myself on this one.

Tesla list wrote:

> 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?

It's funny to me you came up with an 18.6 factor. I ran through this same
scenario about a year
or so ago and found the same factor. I was trying to define energy per bang
into the equation
but also considering the charging cycle into it. I talked to John offline
at different times. I
eventually developed an equation which varied from the 18.6 factor. It was
based on effective
watts after considering the cap charge time, bps, and watts. However, I
still found John's
formula's to be more accurate over a wider range of coils and have put my
little equation on
hold for now.

FWIW, here was my formula:
Spark length = sqrt(sqrt(sqrt(watts)) * eJ) * 16.5

eJ = simply is the basic energy equation(.5*Cp*Vp^2), except taking into
account Cp peak voltage
(Vp) based on the breakrate and allowed charging time.

Take care,
Bart Anderson