# Re: Secondary Topload ( was New formula for secondaryresonant frequency)

```Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Kurt,

On 8 Feb 01, at 7:53, Tesla list wrote:

> Original poster: "Kurt Schraner by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <k.schraner-at-datacomm.ch>
>
> Hi John,
>
> I'm not shure, if I get you right: isn't it widespread design
> the Medhurst coil-capacity to the independently estimated toroid
> capacity (by Bert Pool's equation), then estimating the
> inductance by wheeler's formula, and then calculating the
> resonant frequency by the Thomson formula ? In symbols:
>
> Cmed = (H/D)*K  (with K from the Medhurst table or a fit eqn.)
> Ctop = (1+(.2781-d2/d1))*2.8*sqrt(pi((d1-d2)*(d2/2))/2)  Bert
> Pool's
>
> Csec = Cmed + Ctop  <--- point of concern ??
>
> Lsec = (R^2 x N^2) / (9R + 10B)    Wheeler
> Fres = 1/ (2pi*(sqrt(Lsec * Csec)) Thomson
>
> ...at least it's the way I'm doing it. I'm aware, that the
> addition of the C's is not ultimately correct (as Paul
> Nicholson's detailed analysis shows). And when the coil comes to
> breakout, the topload is in fact expanded by the sparks and ion
> clouds...

There is a problem with that approach that's been known about for a
long time. It is best illustrated if you take, say, a 6" major
diameter torus, plonk it on top of, say a 2" secondary, deduce its
capacitance by one means or another, THEN put it on top of a 12"
secondary. You will end up with a large disparity in the capacitance
value of the terminal between the two situations. In fact, the 12"
coil will hardly notice it's there. The terminal is effectively
shielded by the windings. For a long time now I've regarded the
system as a whole rather than trying to make the bits fit.

Regards,
malcolm

> Soo..., are you meaning, you are using an empirical rule, to
> combine the two capacitances in a more suitable way? I would be
> most interested in it. My calculation, presented in the same way
> as yours from JHTES 3.2, are:
>
>  For the Primary I entered
>   Cap = 0.1094 uf,  Avg Rad = 13.335, and  Width = 6.984
>  For the Secondary I entered  Rad = 7.9,  Turns = 821,
>    TPI = 11.80,  and  Sec Term = 69.59 pf
>  The operating frequency was 67.93 Khz,  Pri Ind = 50,16 uh,
>    Pri turns = 7.12, etc.
>
> The difference is not very big, but you are closer to the
> measured loaded Fres of 69kHz. But what is fairly strange: your
> predicted Fres is HIGHER than mine - not LOWER, what I would
> expect from ion clouds etc.-. So, your capacitance combination
> rule would need a subtractive part?
>
> Greets
> Kurt Schraner
>
> Tesla list wrote:
> >
> > Original poster: "John H. Couture by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>
> >
> > Kurt -
> >
> > I visited your web site and entered the numbers from your B&W coil
> > into the on line JHCTES Ver 3.2 computer program. It appears that
> > your coil's top load capacitance does not change when placed on the
> > when on the coil because of ion clouds, etc. Maybe it was because in
> > the past the program inputs were not accurate enough and the tests
> > were not precise enough. This is something that will have to be
> > researched with further tests.
> >
> > For the Primary I entered  Cap = 0.1094 uf,  Avg Rad = 13.335, and
> > Width = 7.0 For the Secondary I entered  Rad = 7.9,  Turns = 821,
> >   TPI = 11.79,  and  Sec Term = 69.59 pf
> > The operating frequency was 68.72 Khz,  Pri Ind = 49,03 uh,
> >   Pri turns = 7.12, etc.
> >
> > The Sec Term = 69.59 is the calculated pf for the toroid you used
> > and also agrees with the Toroid graph I show in one of my books. No
> > change was made in the capacitance for ion cloud or any or
> > condition.
> >
> > John Couture
> >
> > ------------------------------
> >
> > -----Original Message-----
> > From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > Sent: Sunday, February 04, 2001 12:03 PM
> > To: tesla-at-pupman-dot-com
> > Subject: Re: New formula for secondary resonant frequency
> >
> > Original poster: "Kurt Schraner by way of Terry Fritz
> > <twftesla-at-uswest-dot-net>" <k.schraner-at-datacomm.ch>
> >
> > Paul -
> >
> > thank you very much for the good news about usefulness of my
> > results. I'd like to give you the most complete experimental
> > doc's of my coils, ...but, if it comes to precision: it's a
> > bottomless pit! ;o). Even geometric data appear doubtful!
> >
> > >Paul wrote:
> >
> > <snip>
> > ...
> > > Agreed. In the case of the B&W coil, the lack of a well defined
> > > ground surface provides an ambiguous termination of the external
> > > E-field, so the coil is outside the domain of the formula.
> >
> > In fact, all my measurements suffer from this shortcoming. The
> > situation for B&W may be seen at
> >
> > http://home.datacomm.ch/k.schraner/bw_sec.htm
> >
> > ------------------------------   snip
> >
> > Best regards
> > Kurt Schraner
>
>
>
>

```