Re: Capacitance of a long thin rod (e.g. a spark) (fwd)

---------- Forwarded message ----------
Date: Sat, 18 Jul 1998 02:15:53 -0400
From: Richard Hull <rhull-at-richmond.infi-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Capacitance of a long thin rod (e.g. a spark) (fwd)

Tesla List wrote:

> ---------- Forwarded message ----------
> Date: Fri, 17 Jul 1998 07:29:19 +0000
> From: "John H. Couture" <couturejh-at-worldnet.att-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Capacitance of a long thin rod (e.g. a spark) (fwd)
>   Jim -
>   If the capacitance of the TC secondary is changed by the streamers
> wouldn't this put the system out of tune and stop the streamers?
>   Richard Hull said it was an extreme change implying much more than 5%. He
> did not say how he measured the frequencies with and without streamers under
> high voltage operating conditions.
>   John Couture
> ---------------------------------------------------

A good high power system with more power available than the toroid demands will
streamer regardless of tune in the primary circuit or the resonator's actual
operating frequency!

A lot of folks don't realize the coil will only resonate at the instantaneous
frequency dictated by conditions within the resonator system only!  Primary tune
will never, ever affect system resonance under any circustance.  For some this
will be a revelation.  For others it will be a puzzling thought.  The tuning of
the primary only determines relative efficiency of energy transfer.  If it is
tuned to what happens to be the instantaneous resonant frequency of the
resonator system, max energy transfer will take place.  No running disruptive
coil in the history of coiling while producing big, hot sparks has ever been
tuned to the perfect resonant frequency of any resonator system for more than a
tiny fraction of its run time!

The resonant point of a dead resonator and top load is easily found with a
signal generator and an LED in about 60 seconds.  This is about 5 to 10% more
informative and accurate measure of the Tesla coil than the best equation based
system trying to hit it dead on the nose.  Why?  Because it is bound up in
physical reality at the moment of measurement.  It is also important to remember
that that moment is fleeting and upon application of power even the hardnose
measurements go into the toilet.

If we fire a system and the sparks are X long and we then move the primary tap
somewhere else and they are now X minus something...... well, we can assume
based on the arguments above that the primary ain't workin' in concert with the
resonator.... we are off tune.  The resonator IS working at its proper
frequency....always did.... always will.  We were just starvin' it a bit.
Ticklin' it but not in the right spot.  Tuning for max spark is always a good
idea (at least here at the TCBOR).  When one hits the sweet spot it will be made
manifest.  Once this "running tune" is found, we turn the system off and
accurately measure, with a good LCR meter, the total primary inductance.  A
little back paddlin' through th' math will tell us the APPROXIMATE "running
resonance" of the flaming hot system!

 This is how I do it.  I am also not deceived into thinking that this "optimum"
running tune is more than a +/- 5% mime of the real range of instantaneous
resonator system frequencies.  What it is, is a rough center frequency for this
resonator in  my room with the specific toroid in place at a fixed humidity and
temperature and with the sparks hitting those items it typically hits.

I stress this in my book on the CSN as did Tesla.  The resonator system embraces
much more than the wire and topload.  The system, in dynamic operation, is
non-linear.....So are a myriad of other factors associated with the resonant
frequency determination over even minute intervals of time.  The idea that a
disruptively discharged, high power, large sparking system can be tuned to
within a 5% Delta f about instantaneous system resonance is a pipe dream.

Richrd Hull, TCBOR