# SPARK LENGTH vs. VOLTAGE

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From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Wednesday, January 21, 1998 12:53 PM
To:  Tesla List
Subject:  Re: SPARK LENGTH vs. VOLTAGE

Bill -

Your intuition served you well in coming up with the 5.54 MV for your 13 M
coil using the info from the Kotter & Smith article. It is interesting to
note that the 5.54 MV is bracketed by the voltages that are found using the
equation that I posted earlier on the Tesla List. For example:

40 ft spark   KV = 65 x (40X12)^0.7 = 4895 = 4.895 MV

55 ft spark   KV = 65 x (55X12)^0.7 = 6118 = 6.118 MV

I read the Kotter & Smith article several years ago and took the
information into consideration when working on the equation. However, the
Kotter & Smith info would not be as accurate for Tesla coils because it was
based on a radio transmitter using continuous waves and not a Tesla coil
using dampened waves.

I agree the TC sec voltage cannot be accurately measured, however, it can
be resonably estimated using the correct equation. It is understood the
spark would be from a typical Tesla coil and would be a straight line spark
at standard air conditions.

I also agree that statements are "moot", that is subject to argument and
discussion. In the past a small number of coilers have tried to solve the
TC sec volts problem by building coils and making the necessary tests. I
have used this information when available to develop the above equation. The
equation is speculative but it is all we have at the present. However, it
appears to be doing a resonably good job. I needed this equation for the
JHCTES TC computer program.

Hopefully some coilers will build and test more coils in the future and
publish the data so a more accurate equation can be found. In the future you
may want to use the above equation instead of the Kotter & Smith info or

John Couture

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At 12:47 AM 1/21/98 +0000, you wrote:
>
>From: 	Wysock, William C.[SMTP:Wysock-at-courier8.aero-dot-org]
>Sent: 	Tuesday, January 20, 1998 9:04 AM
>To: 	Tesla List
>Cc: 	ttr
>Subject: 	SPARK LENGTH vs. VOLTAGE
>
>
>Dear List members;
>
>Iike many of you, I have been following the thread on this list
>discussing various thoughts about spark length vs. voltage.
>In particular, I read with interest, Greg Leyh's account of data
>taken on his 45 kw coil.  I don't think any of us have the
>definitive "last word" on this subject, as of yet.  I had (previously)
>posted to the List some comments, based on my own
>experience.  Specifically, I made a reference to a published
>paper in the IEEE.  I encourage others to read this publication.
>It is: Kotter, R.F., Smith, A.N., "A Study of Air-Gap Breakdown
>At 28.5 Khz."  IEEE Trans. Vol. PAS-102, No. 6 (1983) 1913.
>
>In writing about the results I obtained in November, 1995, while
>testing my Model 13M Magnifier coil, I used this reference to
>correct my own work.  I had measured (across a 40 foot gap,)
>an average of 39 arcs/second.  Based on the input power delivery
>rate of 125 Kva, I calculated that there was approximately 0.833 KW
>of energy in each spark, for an output energy delivery rate of
>32.4 KW/second.  The maximum measured (straight line) strike
>distance that was recorded from this coil was 55 feet.  From the
>above reference, taking 8.4 KV/inch (my frequency was higher
>then the reference: 85 Khz vs. 28.5 Khz,) a spark length of 55 feet=
>660 inches=5.54 MV.  This of course, does not come close to what
>I had originally believed to be > 16 MV!
>
>Building a non-inductive resistance voltage divider (and calibrating
>it,) for measurement of R.F. voltages, say up to 100 Khz, will be an
>arduous (and expensive!) task.  Not to mention the physical size
>required, for measuring such high potentials!  Even if someone does
>come up with a workable divider, there is the issue of having it
>calibrated to some known and acknowledged standard i.e., NIST,
>(also an expensive proposition!)
>
>At this point, I would suggest to List members, that statements of
>"x" KV or "x" MV, are moot.  Straight line measured spark length as
>well as disclosure of the gap geometry, may be the only reliable
>and consistent benchmarks we have as tools, to work with.
>
>Bill Wysock
> -------------------------------------------
>Tesla Technology Research
>
>
>

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