Re: Pspice model of Tesla Coil

To: tesla-at-pupman-dot-com
Subject: Re: Pspice model of Tesla Coil
From: Jim Fosse <jim.fosse-at-bdt-dot-com>
Date: Thu, 20 Jun 1996 05:52:25 GMT
Cc: misc3312-at-cantva.canterbury.ac.nz
On Wed, 19 Jun 1996 22:25:07 -0600, Tesla List
<tesla-at-poodle.pupman-dot-com>, you wrote:

>>From misc3312-at-cantva.canterbury.ac.nzWed Jun 19 21:24:24 1996
>Date: Wed, 19 Jun 1996 22:10:49 +0000
>From: misc3312-at-cantva.canterbury.ac.nz
>To: tesla-at-pupman-dot-com
>Subject: Pspice model of Tesla Coil
>
>Hi everyone
>
>I am trying to model a Tesla coil using Pspice.  To start with, I 
>thought I'd try and model the lumped circuit as you would see in any 
>schematic and see what I got.  While I seem to be getting vaguely 
>believable waveforms, the secondary voltage and current magnitudes 
>seem way off (approx 10kV and 200mA peak respectively).

Richard,

The Q of 10 for your primary circuit is within the limits that Malcolm
Watts and others have measured (<12). BUT, your secondary Q is very
low. Malcolm spent most;) of last December building and measuring the
Q of several secondary coils. All had Qs in the 182 to 451 range.
>
[snip; spice net list]
for a spark gap model, ftp over to my ftp site: 

ftp.bdt-dot-com/home/jim.fosse/sgap.lib 

it was kindly provided by the author. Also some pics of Malcolm W's,
Robert S's and my TCs.

>All values are from measurements of my coil, except Rp and Rs for 
>which I have assumed a Q of 10 for the primary and secondary and used 
>this as a basis to calculate Rp and Rs to take into account losses due to the 
>spark gap and arcing from the secondary.

While the Q of 10 for the secondary may be accurate after the spark is
struck; it's not valid for the peak voltage measurement you are trying
to model because you have to get the spark struck to lower the Q to
this value. If the Q were this value to begin with, the voltage rise
(10kV) would never get the spark struck in the first place, so your Q
would be higher! (now that's a circular argument, if I ever wrote
one;)

>  Cs includes my toroid on the top of the secondary.
Your Cs seems a little low to me, my 8" by 20" secondary has a self C
of 13.5pF and my 28" by 4" toroid has a C of 30pF. You may have a
smaller coil though.

I'll send malcolm's Q data to you directly.

cheers,

jim