Re: spark gap question...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Marc, Gary and all,

Interesting discussions! I actually suspect that Marc is correct, and his
coil's performance seems to bear this out. The key difference between the
triggered gap and others may lie in the gap's wider interelectrode distance
versus previously tested gaps. This prevents premature self triggering even
at maximum peak capacitor voltage - the hold off voltage may be 2-3X that
of a normal gap. Once triggered, the "follow through" current from the tank
cap assures good conduction until the first primary current notch. The
combination of wide gap spacing and high velocity air flow may be more
effective in preventing retriggering than any gaps previously tested. 
 
Initially, the main gap must hold off the peak capacitor voltage before
being triggered - typically tens of kilovolts. However, after we've
triggered the gap and transferred most of the bang energy to the secondary,
we have a comparatively long period of low or zero current at each primary
current notch. At (or near) the first current zero, the arc will self
extinguish. At this stage we "only" need to prevent it from reigniting.
However, really only need to hold off the voltage that's induced into the
primary from the oscillating secondary via transformer action. This means
we only need to hold off a few kV since (with the gap open) we will prevent
any transfer of secondary energy back into the primary tank cap. As long as
the gap can "hold off" a few KV, the gap will NOT reignite. This is tough
for most gaps, so they reignite, leading to quenching at the 2nd or 3rd
notch (or worse).

However, all normal static or rotary gaps have much closer gap electrode
spacing - this makes it very difficult to remove sufficient heat and
conductive ions quickly enough to prevent reignition even at a reduced
voltage. Since the triggered gap uses a much wider gap spacing, we'll end
up with a larger voltage drop across the arc as we approach a current
notch. When combined with high air flow, it may be sufficient to prevent
reignition, or at least reduce the number of notches before quenching. We
don't need to completely remove the plasma channel - we only need to
disrupt it sufficiently to recover enough dielectric strength to hold off a
few kV - at a much wider gap spacing.

I'm beginning to believe that the triggered gap has the potential to quench
BETTER than any previously seen gap... certainly better than a SRSG, since
the rotary electrodes are actually coming CLOSER together once they've
initially fired. And it's much simpler! 

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Gary.Lau-at-compaq-dot-com>
> 
> >> Original poster: "Lau, <Gary.Lau-at-compaq-dot-com>
> >> A triggered spark gap can be turned ON at any desired point in time
> >>(provided the electrode voltage is above some minimum value), but the
> >>turn OFF time is still dependant upon the same nebulous factors that
> >>govern any spark gap's quenching.
> 
> >Original poster: "Metlicka Marc <mystuffs-at-orwell-dot-net>
> >this is the misconception, if the plasma channel is being totally
> >removed
> >and only supported by the triggered pulses electrons, then the gap
> >cannot maintain itself without the trigger. this is how i get it to
> shut
> >off when i want it to, granted i'm using a blower that the average
> >coiler doesn't readily have access to, but the average coiler doesn't
> >need it to force quench at will. as long as the arc cannot support
> >itself at any power level and once ignited, cannot support an arc
> >channel, it will shut down.
> 
> Sorry marc, I have to differ.  Plasma in a spark gap will continue to
> conduct for as long as current is able to flow, regardless of trigger
> electrode activity.  Your trigger source is a lamp dimmer discharging a
> cap into some kind of step-up transformer.  The timing of your trigger
> pulse relative to the mains is variable by means of the dimmer control,
> but its pulse width (i.e. the end of the trigger pulse relative to the
> start of the pulse) is not independently controllable, and would have no
> effect if it were.
> 
> I didn't follow you about "if the plasma channel is totally removed".
> If there's no plasma, there's no spark gap?
> 
> Gary Lau
> MA, USA