# Toroid Capacitance

```Subject:
Toroid Capacitance
Date:
Thu, 3 Apr 1997 10:06:49 +1200
From:
"Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Organization:
Wellington Polytechnic, NZ
To:
tesla-at-pupman-dot-com

Hi all,
Based both on results from the charting exercise and some
experiments I am getting closer to formulating something that will
work for being able to calculate this. Like Cself of the bare
secondary, it has to do with size and area of the *total* structure.
I think we can forget trying to use isolated toroid equations. Here's
why:
I just finished building a terminal for my low-f resonator. The
resonator dimensions are 17" dia x 39" high. Cself is about 23pF. The
terminal is roughly toroidal in shape but without the hole in the
middle (oblate spheroid). It is around 26" dia with what would be 11"
ring dia. Popping it right on top of the winding adds a total of about
11 (13? I forget) pF to the structure. Raising it up above the top of
the winding by 5" or so increased C by about a further 2pF.

Now compare this with a far smaller toroid (19.5" x 4.5") placed
on (a) the same resonator (which adds around 6pF to it) and (b) on a
much smaller resonator (which added around 14pF to that one).

You can see that all attempts to use isolated toroid C fly out
the window. BUT, if we look at the size of the toroid as a proportion
of total structure size (and it seems that mounting height variations
should be counted as adding some lump to structure size), we start to
see some sense coming out of these results.

Prelims,
Malcolm

```