Re: Spark gap voltage transients

Hi Alwyn,

	Welcome to the group!

I have sent you my thoughts on secondaries and all of list but the primary
I have always considered as a simple inductor.  I did some experiments
regarding how messy low RF quality wiring vs good RF wiring affects the
primary in my paper at:


along with a number of other papers at:


that deal with primary circuit stuff.

It seems that the initial and zero crossing spikes hit the primary with
sharp transients.  These will set anything in the primary wiring that can
ring into heavy oscillation.  Thus, all the odd harmonics and generally
random looking high frequency stuff that is seen.  Good thick RF wiring
seems to reduce all these little stray capacitances and inductances so they
generate far less noise.  Modeling shows these effects but they are too
complex for a model to reproduce exactly.  If you move the primary wiring a
bit it can all change...

I would ALWAYS put the main gap across the transformer.  The paper at:


shows some experiments with this.  the gap acts as a short to stop the RF
from getting back into the transformer where the RF currents my do bad
things when mixed with the many fine windings of the secondary.  Also, a
good RF filter will really stop the RF so practically nothing gets back to
the neon.  I have a diagram at:


This should be pretty effective.  Some people report that the resistors get
very very hot while others don't seem to have that problem.  The root of
this discrepancy has never been resolved although the resistors can get up
to 300C in "normal" operation...  In my later designs I use only two
resistors and a single safety gap but I am not sure that would work in
every configuration.  



At 01:23 PM 7/22/99 +0100, you wrote: 

This may be old news to some of you expert coilers. Here it is anyway. 

I believe the Tesla secondary behaves as an open circuit transmission line
due to it distributed structure. In which case presumable the primary will
behave similarly except that it s a much shorter transmission line and both
ends will appear to be shorted to the transients.  So that when the spark
gap fires it excites the transmission line characteristics of the secondary
and a damped osculation will be produced superimposed on what I will call
the lumped parameter response of the L and C combination. OK so what. Well
I had assumed that what looks like a damped oscillation in the voltage
waveform was due to the stray capacitance and inductance of the
interconnections and the C. Therefore this could be reduced by better
connections and a C with a minimum of self-inductance. Yes part of the
transient my be due to that effect but the dominate one will be due to the
transmission line characteristics of the primary. I don t think this has
any major practical significance to the design of a system, although it may
be possible to minimise the power loss due this transient by selecting a
particular primary configuration such as spiral or helical. 

In the above I have ignored the power filtering. Particularly in the
configuration were the spark gap appears directly cross the power input,
any filtering circuits will be exited when the gap fires and the resultant
transient may dominate the above effect. Presumable the configuration with
the C directly across the input is the preferred configuration for this
reason. I have always put a bit of series R in the power supplies lines to
reduce the ringing of the power filter. A power supply filter trick is to
put the R in parallel with the L to eliminate its DC effect and reduce its
power rating. The value being calculated such that the resonance is
critically damped. It has the disadvantage that the filtering performance
is reduced. A lossy core material has a similar effect but difficult to design.

Constructive comments anyone.

Regards Alwyn