Spark Gaps

From:  D.C. Cox [SMTP:DR.RESONANCE-at-next-wave-dot-net]
Sent:  Sunday, April 12, 1998 11:18 AM
To:  Tesla List
Subject:  Re: Spark Gaps

to: Steve Falco

Proper gap design is a function of eliminating excessive heat which leads
to a more direct relationship to current as opposed to potential -- this
assumes of course you have a standoff so the high potential isn't tracking
or leaking down the insulator.  A 5 kV potential at 1 Amp requires a more
careful design than a 15 kV unit running 333 ma.  The idea is to "quench"
the gap with enough efficiency to "trap" as much energy in the secondary so
it doesn't try to blast back into the primary where constructive and
destructive interference effects can occur.  Higher currents require more
efficient quenching for proper operation.  The largest consideration, is of
course, the actual peak discharge current of the capacitor in the system. 
This value typically is in the range of 100 to over 1000 peak amperes.


> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Subject: Spark Gaps
> Date: Saturday, April 11, 1998 7:31 PM
> ----------
> From:  Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
> Sent:  Saturday, April 11, 1998 9:02 AM
> To:  Tesla List
> Subject:  Re: Spark Gaps
> > From:  Steve Falco [SMTP:sfalco-at-worldnet.att-dot-net]
> > Sent:  Thursday, April 09, 1998 5:32 PM
> > To:  Tesla List
> > Subject:  Re: Spark Gaps
> > 
> > > Static gaps will work great out to 5,000 watts if the builder has the
> > > experience to apply them.
> > > 
> > > Richard Hull, TCBOR
> > 
> > To what extent is this dependent on voltage and current?  E.g., I can
> > get 5000 watts as 5kv -at- 1amp or 15kv at 1/3amp.  I would expect the
> > static gap to work better in the latter case.
> > 
> > 	Steve Falco
> > 
> Steve,
> You adressed this to Richard Hull, but let me make a few observations:
> When the voltage is lower your gap spacing has to be closer to allow the
> gap to fire properly. With a lower voltage you generally end up using
> a larger capacitor in the tank circuit. This means that you will also
> have larger tank currents flowing when the gap finally fires. This in
> turn translates into larger gap currents. This means more hot ions in
> the gap, and greater gap erosion. 
> Higher voltages allow you to use smaller caps, larger gap spacing, and
> results in lower gap erosion with time.
> You have probably noticed that the main spark gap can take quite a
> beating with your .12 mfd capacitor and dual H&R transformers. A vacuum
> gap is almost a necessity here, if not using a rotary.
> By the way, you can ALSO process more energy in another way: When the
> transformer has a large current capability, you can arrange things so
> that you use a SMALLER capacitor and allow the gaps to fire at a much
> lower voltage. This is usually accomplished by adjusting the speed
> of a non-synchronous rotary gap. As you adjust the speed, you will
> find that there are certain points at which the processed power
> increases dramatically. This occurs, for instance, when the gaps fire
> such that there are TWO gap firings per half-cycle. The transformer
> is charging the cap to a lower voltage, but MORE OFTEN. Thus the 
> actual processed power is increased. With a non-synchronous rotary
> you can actually observe this effect quite readily, for when you
> hit the right spot, the phasing will not be locked in, and so
> you will see the output arcs slowly increase and decrease as the
> phasing slips.
> Because the H&R transformers are quite low as regards voltage, it
> is best to run them matched to the cap such that resonant charging
> occurs. 
> Pole pigs and potential transformers operate quite well
> when running with a rotary gap at higher BPS. Neons do not take the
> abuse too well. It is usually a good idea to include a static gap
> in series with the rotary gap, as this reduces the stresses on the
> rotary and aids in earlier quenching.
> Hope this helps.
> Fr. Tom McGahee