Re: Twin coil spark equation, was Tuning Isis and Osiris

["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 1/12/02 9:17:53 PM Eastern Standard Time, tesla-at-pupman-dot-com
writes:


>
> If we can use John F's equation for spark length, your 96 inches shows 
> a multitippyplier of 1.85. Can I expect a higher multiplier than 1.7 for a 
> well tuned
> coil?



Ralph,

My 1.7 equation is for regular coils only.  Twins give longer sparks
(theoretically 1.41+ times longer), so the equation must be used in
a different way:  First cut the input power in half, then use the 1.7 
formula, then double the spark length result.  

For example lets consider a 1000 watt coil.  If it's a regular
coil, then my formula gives 1.7*sqrt 1000 = 54".   If it's a twin, then
use (1.7*sqrt 500)*2 = 76".  Another (easier) way to get the answer
is to simply use the original formula along with 1000 watts, then multiply
the answer by 1.41.  Still another (even easier) method is to use the...

                      *Twin Coil Spark Length Equation:

            spark length (inches) = 2.4*sqrt input power (wallplug watts)

The reason for all this is because a twin should
be thought of as two coils, each running at 1/2 the power of the total.

*Still, that may not be the entire story.
There are many who say that the interaction of the spark leaders
from each coil creates extra ionization and spark growth which can
make the sparks *longer* than 76".  I've never built a twin, so I
can't say how much extra spark length should be built into the
equation* to adjust for this effect.

Cheers,
John