RE: [TCML] Questions on grounding (hot vs. cool gaps)

["Lau, Gary" <Gary.Lau@xxxxxx>]

Hi Bart,

I would explain the difference in performance between a hot and cool gap differently.  I'm not sure that spark gap resistance differs significantly between a hot and cool gap, that would explain the performance difference.  One could easily argue that when the gap is conducting, there is nothing cool about it.

With a hot gap, one that does not have forced air flow, there are two issues that compromise performance.  Not having airflow to remove hot, ionized air from the previous bangs, the gap's breakdown voltage is reduced, and firing at a reduced voltage hurts performance.  And secondly, the more conductive gasses in the hot gap make quenching more difficult.  So rather than 1st, 2nd, or 3rd notch quenching, you might get 2nd, 3rd, or 4th notch quenching.  I'm totally pulling numbers out of the air here so don't quote me on the specifics, but it's clear that as quenching is delayed, more energy is lost in the gap and elsewhere, rather than going to the topload sparks.  So I believe that these are the underlying mechanisms that yield improved performance with cool, blown gaps.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Sunday, April 19, 2009 3:31 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Questions on grounding
> 
> Hi Dex,
> 
> Yes, if you look at this from a static input power between a hot gap and
> a cool gap. With a cool gap, the loss in heat across the gap will be
> reduced allowing the secondary to gain input power due to the fact that
> when the cap discharges through the primary, the gap resistance has been
> reduced allowing higher currents across the gap and primary resulting in
> a larger emf and energy transfer to the secondary.
> 
> If we limit power to 20A in both cases (hot and cool gap), spark lengths
> will be lower with the hot gap. This is proof that the energy converted
> to power in the secondary has been reduced due to current in the primary
> stage. Keep in mind that power and spark length is a squared law affect.
> In order to double spark lengths, the cool gap must allow 4 times power
> transfer to the secondary. So it's not a 1:1 ratio. If it were, there
> would be far more detail in the output between hot and cool gaps. This
> is why a gap that has twice the losses of a properly cooled gap can
> still achieve 75% of the hopeful spark length.
> 
> Take care,
> Bart
> 
> Dex Dexter wrote:
> > Are you suggesting tesla secondaries receive both more average and peak
> power if static gaps are properly cooled?
> >
> > Dex
> > --- bartb@xxxxxxxxxxxxxxxx wrote:
> >
> > From: bartb <bartb@xxxxxxxxxxxxxxxx>
> > To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> > Cc:
> > Subject: Re: [TCML] Questions on grounding
> > Date: Thu, 16 Apr 2009 18:12:45 -0700
> >
> > Likely a small change in power in one direction or the other. A hot gap
> > will fire at a lower voltage at a faster rate. A cool gap will fire at a
> > higher voltage at a slower rate. I don't think there is a large power
> > factor difference. But there is a difference in the resistive losses
> > across the gap between the two (to some degree), so there will be some
> > change in the non-reactive region. I'm not sure that the differential
> > value is even worthy of noting, but it might be. Good question.
> >
> > Take care,
> > Bart
> >
> > Dex Dexter wrote:
> >
> >> Does that mean that power input (W) increases while apparent power drawn
> (VA) remains aprox. the same in a cooled static gap tesla transformer?
> >>
> >> Dex
> >>
> >> --- chriskarr4@xxxxxxxxxxx wrote:
> >>
> >> Hello Joe,
> >> The reason that a fan on the spark gap helps improve output of a Tesla coil is
> that it helps to extinguish the arc and blow out the ions. When the ions are all gone,
> the gap takes a higher voltage to make it break down, which means that there's
> more 'bang energy', resulting in more energy transferred to the secondary coil and
> that means larger streamers on the output.
> >> Christopher
> >>
> >>
> >>
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