RE: Power Loss

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Hi Jared:

My "dangerous advice" comment stems from the likelihood (IMO) that
setting the gap width as you suggest may result in damaging the NST.

Let's say that one opens the spark gap completely, so it never arcs.
Assume also that the cap is mains-resonant with the NST, as is the case
with a .01uF and a 15/60.  With each mains half-cycle, the cap voltage
will build higher and higher, as you have a 60 Hz resonant tank circuit
and nowhere else for the energy to go.  Normally a "properly" set gap
would break down at a voltage corresponding to what's "safe", before the
1st half-cycle even completes.  But if the gap is set wider to a voltage
higher than "safe", the voltage will build on subsequent half-cycles to
higher and higher voltages, until something DOES break down.  It's
entirely possible that your 15/60 NST may be charging the cap to 40 or
50kV if the gap is set so wide.  You may be lucky and have good
insulation on your NST, but another person's NST may fry if it sees
40kV.

I agree that a too wide gap won't fire at all, and particularly with a
mains-resonant cap, that's a perilous situation that should NEVER be
allowed to happen.  As you continue to close the gap, it will fire at
voltages far in excess of what's safe for the NST, and spark performance
will be excellent, provided the NST doesn't die.  Still continuing to
close the gap, the breakdown voltage will go down as the gap width
decreases and performance will also go down.

The accepted methodology for setting a static gap is to apply just the
NST secondary across the gap at maximum Variac, and adjust the gap width
so it just barely fires.  This sets the breakdown voltage to the peak
secondary voltage, or about 21kV for a 15kV NST, which is the maximum
voltage it was designed to endure.  OK, maybe open it up just a tad more
if you're feeling lucky...

I don't understand your comment: "a gap that is to small will not quench
properly."  Why would quenching - the cessation of pri/sec energy xfers
when the gap stops conducting - get worse as the breakdown voltage of
the gap is reduced?  It's no mystery that performance diminishes as the
gap is reduced, due to smaller bang size, but I would think that
quenching may actually improve with smaller bangs.

Regards, Gary Lau
MA, USA


> Original poster: Jared E Dwarshuis <jdwarshui@xxxxxxxxx>
>
> The sum of gap distance is around one half inch for the forced air gap
> that we have used for the last two years. We use a .01uf tank
> capacitor with a 15/60 NST and have had no problem. (I don't
> understand the dangerous advice comment).
>
> As far as closing the gap, you simply do so, until you observe a
> slight output of power then you stop, not complicated.
>
> There -is- a sweet spot range when tuning spark gaps. A gap that is to
> large will not fire at all and a gap that is to small will not quench
> properly.
>
> If you try to make a tank circuit that operates on low voltage but
> relativly high current it quickly becomes apparent that the gaps need
> to be fairly close just to fire. But the high current keeps the closed
> up gaps from quenching. Thus coilers use relatively high voltage and
> low current to get their power. High voltage and low current allows
> coilers to use an air gap system.
>
>   Sincerely: Jared Dwarshuis
>
>> Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
>>
>> Ouch!  This sounds like dangerous advice.
>>
>> With the original poster's 15/60 NST, your suggested .01uF cap would
be
>> precisely mains-resonant.  If the gap were opened for maximum spark
>> length, that would surely result in higher than safe voltages for the
>> NST.  Spark performance would be impressive, though short-lived.  A
>> half
>> inch wide gap is much too wide.
>>
>> Spark performance is monotonically correlated to gap width; there is
no
>> sweet spot.  The performance will increase as the gap is wider, until
>> either losses and NST Q allow no further mains resonant rise, or
>> something breaks down.  How do you tell when to stop closing the gap
>> based on performance?  It seems closing the gap would continue to
>> reduce
>> the spark performance all the way down to zero.
>>
>> Gary Lau
>> MA, USA