Simulated tesla coil

From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Monday, April 13, 1998 7:53 PM
To:  Tesla List
Subject:  Re: Simulated tesla coil

Tesla List wrote:
> ----------
> From:  ESchulz531 [SMTP:ESchulz531-at-aol-dot-com]
> Sent:  Sunday, April 12, 1998 1:03 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Simulated tesla coil
> All,
>      I tried simulating my tesla coil with Electronic Workbench it uses a
> spice engine.  It worked pretty good but I think what I am seeing on the
> simulated o-scope is wrong.  Can somebody tell from my PIC what is wrong.
> PIC - http://members.aol-dot-com/tesla00  look in advanced theory
> Erik


It certainly does look wrong. The main problem is probably the model for
the gap. A spark gap fires at an initially high breakdown voltage, then
rapidly changes to a high conductive state, "recovering" only when the
current drops low enough so that the incandescent cathode spots can no
longer be maintained. If the current is stopped briefly, but the gap is
not allowed to fully recover, it will reignite at a much lower voltage.
The model you're using appears to be turning off prematurely,
while there's still a large amount of primary current circulating
through the gap, and doesn't simulate the real-world behavior of an
air-insulated gap.

As I'm sure you know, modeling a spark gap is not a trivial task, and
even the best models are only approximations due to the various
non-linear characteristics! As a first approximation, try using
back-to-back series connected 5-8 volt zener diodes in series with a
controlled switch - and set the model so that the switch opens only when
the primary energy (1/2 LI^2 + 1/2 CV^2) is zero. BTW, what value of
primary:secondary coupling coefficient did you use?

-- Bert --