# Re: John's formula, spark length

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

Ed,

My formula is not for the average coil, it is only for efficient
coils.  If a coil needs to be large to be efficient, then my
formula would call for that.  This formula does not take into
account the size of the coil.  The purpose of the formula
is not to predict how long the sparks will be from a particular
coil.  Rather the formula predicts the longest possible spark
length using a particular input power.  It is assumed that the
most efficient size and design will be used to achieve these
optimal results.  Of course some extremely efficient coils
may do a little better than the formula predicts.  It's only a
guide, and only a guide for efficient coils.

I define an "efficient coil" as one that can give the longest
possible sparks for a given input power.  This is not the
true engineering definition of efficiency of course.

I personally don't know if your coil would give much longer sparks
if it was wider, for the same input power.  It may, since the
inductance would be higher.  Sometimes much the same effect
can be achieved by using a somewhat thinner wire with more
turns.  Of course if the wire is too thin, the performance will
be poor.  It's a balancing act.  I consider the length of the coil
(the height) to be a very important factor in determining power
handling capability also.

John

>
> Haven't looked at John's page for a while.  Does the formula somehow take
> into
> consideration the size of the coil?  My 6.0" diameter coil which I run at
> 6kva should produce about 132" sparks according to the formula.  The best I
> have achieved is 104".  I do believe that a 10" or 12" diameter coil with
> this
> much power input could certainly produce 132" sparks.  For a given size coil,
> there is a maximum level of power that can be input to the system.  By just
> using the formula, one could expect 132" sparks with 6,000 watts input to a
> 3.0" diameter secondary - which I don't think is feasible.
>
> Sometimes I think I am on the verge of destroying my secondary at 6 kva.
>
> Ed Sonderman
>

```