From: Paul
Date: Mon, 25 Dec 2000 13:29:54 +0000
Subject: [TSSP] Capacitance between primary and secondary
Terry Fritz wrote (on tesla list):
> I retook the physical measurements of my coil and measured the
> capacitance from primary to secondary.
>
> I have the center of the primary plane 16.875 inches off the floor.
> The inner primary radius is 5.95 inches.
> There outer radius is 13.38 inches.
> The primary tubing diameter is 0.252 inches.
> There are 19.563 primary turns.
> The secondary is still 10.25 x 30.0 inches.
> There are 1000.5 turns
> The secondary wire is 0.0201 inches in diameter.
> The split 6 leg foil ground plane is on the floor but it is not connected
> to anything.
> The primary and secondary are floating.
> My primary and secondary spiral (out and up) in the same direction.
>
> Pictures at:
> http://hot-streamer.com/TeslaCoils/Temp/acmi1.jpg
> http://hot-streamer.com/TeslaCoils/Temp/acmi2.jpg
>
> The primary to secondary capacitance measures:
>
> Height (inches) Capacitance (pF)
> 0 42.2
> 1 36.4
> 2 33.7
> 3 29.4
> 4 27.6
> 5 25.8
> 6 23.6
> 7 22.6
> 8 21.8
> 9 21.1
> 10 19.8
> 11 19.4
> 12 19.0
> 13 18.5
> 14 18.0
> 15 17.6
Terry, I fed your dimensions into the new capacitance matrix
generator, for the height 0 and height 15 cases.
For height 0 I get the direct physical cap matrix elements:
primary to groundplane: 24.0 pF
primary to secondary: 26.7 pF
secondary to groundplane: 22.5 pF all +/- 3%
so the measurement between primary and groundplane will read
the total capacitance as given by
26.7 | ( 22.5 # 24.0) = 26.7 | 11.6 = 38.3pF
where | means 'in parallel with' and # means 'in series with'.
I guess your presence in the field will have added a little more
parasitic capacitance to bring the reading up to the measured value.
The corresponding predictions for the 15" position are
primary to groundplane: 27.1 pF
primary to secondary: 5.9 pF
secondary to groundplane: 28.2 pF all +/- 3%
which gives a measurement of
5.9 | (27.1 # 28.2) = 19.7 pF,
a little high of your 17.6 reading - not sure why.
These capacitances are significant sizes and will have to be taken
into account in the tssp simulator when primary coupling is
introduced, although for acmi I should think they can be safely
ignored.
You might like to know that the new cap program generated the full
distributed capacitance matrix for these two coil positions in a
little under 15 minutes - quite an improvement in performance,
which brings the prospect of being able to model a large number of
coils that much closer.
Cheers,
--
Paul Nicholson,
Manchester, UK.
--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.