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Re: Spark Gap Replacements >> Subject: Spark Gap Replacements
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> Subject: Re: Spark Gap Replacements
> >Subject: Re: Spark Gap Replacements
> >> Subject: Spark Gap Replacements
>Subscriber: bert.hickman-at-aquila-dot-com Sat Jan 4 21:49:19 1997
> Date: Sat, 04 Jan 1997 11:34:05 -0800
>From: Bert Hickman <bert.hickman-at-aquila-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: Spark Gap Replacements >Subject: Re: Spark Gap Replacements
>> Subject: Spark Gap Replacements
Tesla List wrote:
>
> Subscriber: FutureT-at-aol-dot-com Fri Jan 3 22:12:34 1997
> Date: Fri, 3 Jan 1997 18:20:19 -0500
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: Spark Gap Replacements
>
> <<
> >Subscriber: bert.hickman-at-aquila-dot-com Wed Jan 1 21:42:58 1997
> >Date: Wed, 01 Jan 1997 10:06:26 -0800
> > From: Bert Hickman <bert.hickman-at-aquila-dot-com>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Spark Gap Replacements
>
> Tesla List wrote:
> >
>> >> Subscriber: FutureT-at-aol-dot-com Tue Dec 31 22:56:47 1996
> >> Date: Tue, 31 Dec 1996 16:02:10 -0500
> >> From: FutureT-at-aol-dot-com
> >> To: tesla-at-pupman-dot-com
> >> Subject: Spark Gap Replacements
> snip-snip
>> > >Best spark occured when "quench" occured at the first RF notch. A
small
>>>> neon bulb placed at the top of the secondary coil lighted most
brightly when
>>>>quenched" at the the first RF notch. Resonant frequency = 500 kHz, Pulse
>>>>rep. rate = 200 to 1000 PPS.
> >>>snip
> > >> The purpose of this work was to explore the benefits of fast
"quenching",
>>>and avoid the difficulties of 1st notch quenching in actual spark-gap
TCs.
> >
> > >> John Freau
>
> > >John and all,
>
>> > Thanks for the update! This is an area I'd like to further explore when
>>>time permits, though probably with power MOSFETS or IGBT's instead of
> >>straight bipolars, for the same reason - investigating quenching. In
>> >your work, did you see any surprises, or did experiment seem to match
>> > theory?
> >
> >-- Bert, Richard --
> >>
>> No surprises, but I really need to improve the system before real
conclusions
>> can be drawn. Richard Hull's hydrogen thyratron method may be the
"ticket"
>> to answering these quenching questions.
>
>I completely agree! Way to go Richard!! Sometime down the road, maybe
> he'll provide us with some further info on how he controls this
>beastie... :^)
Richard, I agree, this was great work using using the thyratron!! Now if
there were only some winter hamfests around here......
> > BTW, Bert, did you measure the quench-time of your system when it
quenched
>> on the 1st notch? More details such as k value, frequency, and
>> quench-time, would be appreciated. I guess what I'm asking is the same
>> question you asked me, were there any surprises?
>No surprises, but the best I've ever done is quench (intermittently) at
>he END of the first primary->secondary energy transfer. However, when
> this DID occur, it occurred at the predicted time, and peak secondary
>output always corresponded to this case. I've never been able to quench
>BEFORE the end of the first energy transfer from primary to secondary.
> Since my "k" has always been in the range of 0.153 to 0.22, this means
> I'll always see at least 5 to 7 half-cycles of primary current while
>energy transfers between primary to secondary.
Since it seems "almost" impossible to quench on first notch, it seems even
more "impossible" to quench before the first notch (using a spark-gap) --and
I agree, such an early quench will degrade the spark severely as shown by
theory and Richard Hull's work.
>> There seems to be a
> >question in my mind about what's really happening waveform-wise, during
>> pre-first notch times. My quench time was about 4 uS at k = .09, at 550
> >kHz, or somewhat longer than TC tutor advocates, yet I saw no "wave
packets"
>> in the secondary RF. This quench time gave me the longest sparks.
>
As indicated in interim posts, I incorrectly reported the 4 uS quench
time--it was really 8 uS. This shows the perils of working from memory, and
not verifying everything, sorry for the confusion! Also Upon re-checking
everything, TC tutor agrees with the 8 uS quench-time. From reading this and
your other posts, I would say we agree on the quench scenario. BTW, TC
tutor takes primary losses into account and gives very good quench time
predictions. Now back to your answer:
>Excellent question!! Lets make sure we're talking precisely about the
> same thing. Assume that the gap does not quench, and "fires" at time
> t=0, and that the uncoupled resonant frequency of the primary and
>secondary is Fr. If we look at the secondary's RF output, we'll see an
> envelope of oscillations of frequency Fr starting from 0 and hitting a
> maximum at t=T1, going back down to 0 (T2), climbing to another
> lower-amplitude maximum (T3), going back to 0 (T4), and so on. If we
>looked at the envelope of the primary current oscillations, we'd see it
>rise to a maximum 1/4 cycle (of Fr) after t=0, go to a minimum at about
> T1, rise to another lower-amplitude maximum at T2, a minimum at T3, and
>a still lower maximum at T4, and so on. As you are aware, the so-called
.>"magic k" values are those which result in time T1 being equal to an
>_integral number_ of half-cycles of Fr. If you are looking at the
> secondary waveform, the first "notch" would be at t=T2; if you're
> looking at the primary current, it would be at t=T1. Lets assume you're
>looking at the secondary RF output.
If you quench anytime between 0 and t=T1, you'll only see a single ring
>up of energy into the secondary, and a longer-period ring down. This is
> the time where energy is being transferred, ONE WAY, from the primary to
> the secondary. If you quench sometime between T1 and T3, you'll transfer
>energy back, ONE WAY, from secondary to primary, and will be past the
>point of ideal quench. Except for when k=0.6, the ideal quenchtime
>always be at a point _after_ the first primary current zero-crossing.
>The great majority of us have "lousily" quenching gaps - we can't quench
>at T1, and are forced to quench at the second, or sometimes even the
> third, minimum primary energy points (i.e., T3, T5...). Much of the
>secondary energy now gets transferred back into the primary and expended
>in the gap! By the time we begin to again transfer energy back into the
>
> I now believe the quenchtime design objective should be to hit somewhere
>between 80-90% of predicted T1 - quenching a little early is much better
>than letting a good portion of it transfer back into the primary! As
>Richard Hull has pointed out earlier, this ALSO seems to avoid problems
>with actually seeing the effects of frequency splitting. However, you
> CAN get too much of a good thing if you cut it much too short,
> particularly for lower k values. Unless you take heroic measures, or use
>an electronic switch/thyratron, you'll have extreme difficulty quenching
> at any earlier zero crossings of primary current (Ip). You wouldn't want
>(and probably couldn't) quench at times where Ip >> 0. And, from an
>energy transfer standpoint, there are no clear benefits in doing so.
> Now, with this in mind, lets look at your example above. With k = 0.09
> and Fr = 550 kHz, the approximate "beat" frequency (Fb) would be about
>k*Fr or about 49.5 kHz. The corresponding time between "notches" would
>be 1/Fb or about 20 uSec, and the theoretical "ideal" quench time (T1)
>would be about half of this, or 10 uSec. If you were _actually_
>quenching at 4 uSec, then this would have been before the first
>primary-secondary energy transfer had gone to completion. This would
> explain why you observed no "wave packets" in the secondary RF - you
>quenched before T1, so there _was_ no energy transfer back to the
>primary! If TC tutor was advocating an even shorter time, then it was in
error!
I agree, and regarding TC tutor, again, I was in error, not TC Tutor.
>>However, this does not explain why a 4 uSec dwell gave you the longest
> sparks. Only about 5 half-cycle energy transfers would have ocurred,
> when the low k value suggests that at least. Could gap arcing have
>increased your "effective" dwell to a longer time?. If this was truly
>the effective quenchtime, then something very interesting is going on!
>How did you actually measure the quenchtime? TAlso, this would be about
>"on the money" if your k was 0.19...
You are correct, as mentioned above, my quenchtime was actually 8 uS rather
than 4 uS. Quenchtime was measured by O-scope. Again you are right, when I
obtained the ~4 uS quenchtime this was at ~k = .22. (This post will teach me
to verify my figures before posting!)
>> > Bert, did you try "degrading" your quench to the 3rd notch (down from
the
>>> alternating 1st or 2nd), to gauge the effect on the spark length?
>Yes, and beyond. By switching off the air-flow and vacuum to the gaps, I
>can "saturate" them as I increase input power - thereby causing them to
>quench at later transfer cycles. Secondary streamer length climbs with
>increasing power, peaks out, and then begins significantly shrinking to
> perhaps no more than half the maximum length.
Increasing power? Do you mean variac input power, or or you mean power due
to energy transfer from pri to sec? I assume the shrinking spark occured at
"later" notch quenchings? How many notches were needed to reduce the spark
to half its maximum length would you say?
>The gaps also "brighten"
>significantly from the additional energy being dissipated, and they make
>a distinctly "duller" sound. I've always focussed on trying to get from
>two energy transfers down to one. Quenching later consistently gives
>poorer output performance, both theoretically and practically.
>
Thanks for the info on your system. This data parallels my own findings.
BTW , do I understand correctly that your tests were done at 1 or 2 kW or
higher? This seems to give hope to the idea of quenching on the first notch
without using a thyratron, although I do want to try the thyratron method.
Quench is best at first notch, earlier is NG as shown by Richard Hull's
excellent thryratron work, and later is NG as shown by all of our work.
>> > John Freau
> Safe coiling to you as well, John!
>-- Bert --
>>
Happy coiling,
John Freau