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Re: [TCML] still stuck at 36



Hi Bart,

You're correct that the details are important.

At lower RF frequencies, and if the  coil quenches on for example the
5th notch, and if the break rate is lets say 300 bps, the 1000x situation
won't hold.  The total time the gap is lit during one bang could be
200uS.  And if the cap has 3000uS to charge between each bang
then it's a 15X ratio which is somewhat significant.  But quench time
is not a huge factor, that's why I said the quenching only needs to
be adequate (not excellent).

What often occurs if there's not enough airflow is that the gaps
will run hot.  This will cause the gaps to fire at a lower voltage and
greatly reduce the bang size, and increase the break rate.  This
greatly reduces the spark length.  This factor is what hurts the
spark length the most; the reduced firing voltage when the gaps
heat up.  And if the gaps heat even more, then true 60Hz power
arcing can occur which completely or partially prevents the cap
from charging.

Regarding the early quench scenario... it never happens. It's impossible. If the gap fires, the best it will quench at is first notch (never sooner), due to air flow. When there's too much air flow, the gap won't quench early, instead it will simply fail to fire at times. This is a point that is often misunderstood.

I agree that the gap resistances don't increase the transfer time very much,
and are not a large
factor in gap losses. Gap losses are more due to having
multi-gaps.

I go back to what I said that a single gap has less losses than a
multi-gap, but a single gap is harder to quench and harder to keep
cool, so it needs more airflow.

To summarize again:

1)  Poor quenching can reduce the time available for cap charging,
but is a minor factor. Also I believe it's mostly the first transfer energy that
determines the spark length, with subsequent transfers contributing
little or nothing to the spark length.

2)  Hot running gaps will fire at a lower voltage and give a smaller
bang size which reduces the spark length.  This is a very large
factor. (need more air flow)

3)  Even hotter gaps will power arc and prevent cap charging and
kill the spark length severely.  (need more air flow)

3)  Too much air does not cause a too-early quenching.  Too-early
quenching is impossible.  Instead too much air prevents gap firing
at times.  (need less air flow)

4)  Multi-gaps have higher losses and give shorter sparks, but
quench more easily, and run cooler with less air needed.

So there are a number of issues to consider.  But it's a logical
progression to first select a low-loss gap (single gap), then
cool it with air because single gaps run hot and may have
trouble quenching or may start firing at a lower voltage if
too hot.  Also make sure there isn't so much air that the
firing
is interupted at times.  A steady firing is needed.
There's no need to worry about quenching too soon,
that can't happen.

John



-----Original Message-----
From: bartb <bartb@xxxxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Tue, 27 Jan 2009 8:44 pm
Subject: Re: [TCML] still stuck at 36


Hi John, 
 
The single gap with low loss sounds reasonable. The idea of quenching sluggishly, well, some variation is possible, but the consequence is not a cap charge issue. The charge time on a typical coil versus the maximum energy transfer time is over 1000x. For my 4.5"D coil, a 12/60 NST charging a .0188uF cap, charge time is 18.8ms for 120bps operation versus a 17.16us for complete energy transfer (3.9 cycles at 230kHz). If we quench slowly, the cap has all day to charge since the 17us makes little difference (0.01% of charge time). 
 
A quench variation entails a quenching early scenario which would leave a charge on the cap (and energy in the cap). The cap would then charge to breakdown more quickly to the next due to the charge left on the cap (the line between A and B just got shorter, bps increases, spark length diminishes). But this also states that all the energy in the cap did not make it through the transfer (this is why spark length decreases and not so much the bps which was simply a result). I think nearly all of the energy transfers, an d so much so, that the voltage left on the cap is insignificant in the same fashion as the ratio between cap charge time and energy transfer time, and more so in a static voltage clamping gap as opposed to a rotary. 
 
Energy transfer time does make a difference of course (energy and time). But the gap cannot affect the energy transfer time significantly by quenching early (but it can by preventing extensions of the transfer time in an extremely bad situation). This would be due to gap impedance. 
 
Energy transfer time is based on the mutual inductance and frequency. For my 4.5"D coil, reactance as based off of the mutual inductance is 123 ohms. If the gap was ridiculously lossy, it's resistance would add to this reactance. In a completely theoretical case where the gap resistance was equal to this reactance, the transfer time would be double. It is still insignificant regarding cap charge time. However, the em force enveloping the secondary would certainly be reduced (time and energy), and this would affect energy stored in the top load. 
 
But now for the gotcha! Gap resistances are less than 1 ohm. So gap losses are not affecting energy transfer times. I think it's all about simple power losses at the gap that are the real cause of pain and suffering with spark lengths which is why significant air cooling drastically improves any static gap style (some styles are better than 0D others at accomplishing this). There is always the issue of too high a velocity at the breakdown point that blows out the spark. This is a quenching early issue, which of course doesn't transfer "all" the energy in the cap and thus we see spark lengths diminish and bps rise. This is why some find using a variac on the air voltage is not always best at 100%. 
 
Hope I'm making sense. Sorry for being long winded, but it's one of those "devil in the details" subjects. 
Best Regards, 
Bart 
 
futuret@xxxxxxx wrote: 
I think what makes a hyperbaric gap perform well is that it's 
a single gap. This makes it a low loss gap. Once you have a 
low loss gap then all that's needed is to quench it adequately. 
Since a single gap is harder to quench than a multi-gap, this 
is why a good amount of air flow is needed. 
 
The air flow is 
also needed to cool the electrodes. If there's not enough 
air flow the gaps may run too hot and may begin to power arc, 
or quench very sluggishly. If a gap quenches too slowly, 
then less time is available to recharge the capacitor and 
output suffers. 
 
If there's too much air, then 
the gap may fire intermittently with a sort of stuttering 
action and this cuts the spark length too. It's not really 
over-quenching, it's simply erratic firing=2
0in the first place. 
It's not that the gap quenches too fast, rather it's that 
the gap does not fire consistently. 
 
John 
-- > 
 
-----Original Message----- 
From: DC Cox <resonance@xxxxxxxxxxxx> 
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> 
Sent: Tue, 27 Jan 2009 4:58 pm 
Subject: Re: [TCML] still stuck at 36 
 
 
 
It's not clear why to me either. My best guess is better cooling due to the 
high velocity air, and perhaps increased turbulence 
around the ends of the copper pipes. 
 
I know that most coils performance jumps in amazing quantity of spark output  when the hyperbaric gap is used. I have never used it above 4 kVA as
single gap, but did some experiments at 7 kVA with a dual series >
hyperbaric 
gap and it seemed to work as good as a small rotary. 
 
Perhaps looking at scope ringdowns with and without a hyperbaric gap might 
provide some clues. 
 
Dr. Resonance 
 
 
 
 
On Tue, Jan 27, 2009 at 1:51 PM, Lau, Gary <Gary.Lau@xxxxxx> wrote: 
 
I don't disagree that hyperbaric gaps work well, but I'd like to be
clear 
on why. Too often on this List, the word "quenching" is used >
incorrectly. 
My measurements showed conclusively that hype
rbaric gap losses were
lower 
than in a sucker gap, but I made no attempt to measure actual >
quenching. 
Quenching is unrelated to gap losses and refers to how many pri-sec
energy 
trades occur before the gap extinguishes. In fact, I think that >
typically, 
lossy gaps (at least multi-segment gaps) have superior quenching. 
 
So, have you seen evidence that actual quenching, as observed on a >
scope, 
was superior with the hyperbaric gap? Was this with free-air >
streamers or 
grounded (connected) streamers? Seems like a very difficult thing to 
accurately compare between two systems. 
 
Regards, Gary Lau 
MA, USA 
 
> -----Original Message----- 
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx]
On 
> Behalf Of DC Cox 
> Sent: Tuesday, January 27, 2009 1:31 PM 
> To: Tesla Coil Mailing List 
> Subject: Re: [TCML] still stuck at 36 
> 
> Bill: 
> 
> What was your maximum spark before you used the hyperbaric
sparkgap? 
> Also, put a variac on the vac. cleaner motor, and fine adjustment
of the 
> speed will increase your output even more. Usually best output 
> around 75% of the variac. 
> 
> I know they work great. They always increase your sec spark output 
20> dramatically which means we have been underquenching 
> with most of our previous designs. 
> 
> Dr. Resonance 
> 
> 
> 
> 
> On Tue, Jan 27, 2009 at 5:50 AM, Bill Bohn <b.jbohn@xxxxxxxxxxx> >
wrote: 
> > I built the hyperbaric gap as described WOW!Now I get 44" I am >
using a 
shop 
> > vac for suction.I am using 5 of the 6 strings of caps.I think I
did 
some 
> > damage 
> > 
> > To my 5-1/4 coil.Now I have a 6.625" secondary wound 26.5" 1060
turns. 
Top 
> > load is 4.5x18 toroid and a 7" sphere.Seems best with the
primary 
clamped 
> > 
> > At turn 5.The spark sounds somewhat eratic and choppy.IT will >
smooth 
out 
> > some by adjusting the spark gap closer at the loss of streamer >
length . 
> > 
> > What is the method of measuring BPS?IT doesn't seem to sound >
right.The 
> > coupling between primary and secondary is 0.I am going to put
the > 6 
strings 
> > of 
> > 
> > My mmc cap in but I think it will be best tuned at about turn 2
and 
become 
> > even more erratic. 
> > 
> > I am getting positive results and thank everyone for all the >
ideas20and 
2 
> > cents worth. 
> > 
> > _______________________________________________ 
> > Tesla mailing list 
> > Tesla@xxxxxxxxxxxxxx 
> > http://www.pupman.com/mailman/listinfo/tesla ;
> > 
> _______________________________________________ 
> Tesla mailing list 
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