RE: True Toroid Capacitance

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

Original poster: "John H. Couture" <couturejh-at-mgte-dot-com> 


Malcolm -

I agree that using a fixed percentage of toroid reduction does not appear to
be realistic. The wide range of true toroid capacities for the same toroid
requires testing each TC for the resonant frequency after it is built. This
resonant frequency will give you the true toroid capacitance in the JHCTES
Ver 3.42 TC program and will always be less than the theoretical
capacitance. The accuracy of the toroid capacitance will depend only on how
well you do the test and enter the inputs, no assumptions will have to be
made.

Your experiment with the 8" major dia toroid is the perfect demonstration to
show the dramatic behavior of the toroid capacitance when in the real world
of Tesla coils. As you indicate the  capacitance was less than one pf when
placed on the 17" coil. This indicated a very large capacitance reduction of
about 90% from the theoretical capacitance! In the test where this 8" toroid
was placed on the 2" coil and showed a significant difference (larger
capacitance?) this would indicate a very small reduction from the
theoretical capacitance. It is obvious that the same toroid can have a wide
range of capacitance reduction from the theoretical capacitance. In your
tests the range was about 10% to 90% toroid capacitance reduction!

The es fields around the TC, toroid, and including surrounding effects are
very complicated and to make calculations work assumptions have to be made.
However, the accuracies using these calculations in programs appear to be
acceptable. Because the frequency test takes everything into consideration
it can then be used to verify the accuracy of the programs after the TC is
built.

Using the resonant frequency test to verify the true toroid capacitance
reduction is relatively new and there is very little  data available to
compare the TC computer programs with the results of the tests. Hopefully
more coilers will make these tests in the near future.

John Couture

-------------------------------------

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, November 05, 2003 10:17 PM
To: tesla-at-pupman-dot-com
Subject: RE:True Toroid Capacitance


Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz>

Hi John,
           I'd like to add a comment to your piece based on my own
experimentation. We have seen, from various sources, a percentage
reduction figure in Ctor when placed above a coil to account for the
disparity. But the problem is not that simple. Some time ago I
checked some extremes to determine the mechanisms involved. The most
radical of these was to pop a 8" (major) diameter toroid on top of a
17" diameter coil. The capacitance added was less than a pF
(according to the change in Fr) yet the same terminal caused a very
significant difference when placed above a 2" diameter coil (don't
ask me to quantify it - it was so long ago I forget the figures).
However, the 2" case was in the 10%-type range, in other words, more
than notable. Point is, a fixed reduction percentage figure will
apply only for a limited set of size - size ratios and is therefore
invalid in general. However, I see no reason why a figure for a
particular coil and torus cannot be calculated with a modicum of
precision based on a consideration of e.s. fields and possibly even
just a mechanical size vs size rule (including of course pacement
height of the toroid above the windings).

Malcolm

----------------------   big snip