RE: spark size and JOHN FREAU's FORMULA

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

Original poster: "Mccauley, Daniel H by way of Terry Fritz <teslalist-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>



John Freau's formula does work well for the most efficient of coils.
However, I think the formula may be
misleading as this coil defines what the most efficient tesla coil would be
able to obtain.  I think for
someone building a "first" tesla coil that could probably expect to get an
streamer length of about
50-75% of this value, perhaps even less.

For example, in our latest Table Top Competition, the results are as follows
where max theoretical arc
length is based upon John Freau's formula:

POWER		ARC LENGTH		MAX. THEORETICAL ARC LENGTH
143		13"			20.32"
184		10.75"		23.05"
152		10"			20.95"
152		9"			20.95"

As you can see, even in this competition category, these coils are all
putting out less than 50% of the
maximum arc length determined by John Freau's formula.  Only the first entry
puts out slightly more than
50%.  Of course this data is based upon 4kV tesla coils.  The efficiency of
coils may increase in proportion
to the primary voltage etc..., however I do not have data at this time to
back that assumption.

So in summary, Paul, if I would be very happy if you got your coil putting
out anywhere over say
15 inches.  Anything over 20 inches with a 9kV/30mA NST and I'd say you have
an excellently built coil ! ! !

Good Luck

Dan






Hi Paul,

John Freau's formula seems to work very well:

Spark length in inches = 1.7 x SQRT (power input)

So a 9/30 NST is 9000 x .030 = 270 watts and the spark length is 28 inches
if everything is perfect.

Cheers,

          Terry



At 05:16 PM 1/3/2003 +0000, you wrote:
 >Hello all, hope you have had a good festive season.
 >
 >I have had a look around at all the formulae and keen to start the
 >construction of my first coil, one thing I have been unable to determine
 >(other than it depends on ambient conditions) is the size of ark. Is there
 >any formula for determining the size of ark you are likely to produce ?
 >
 >
 >Paul