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Re: 2 questions on resonance

Hi Gary,

At 10:17 AM 4/7/99 -0400, you wrote:
>>Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>>
>>Dear all,
>>          After reading the responses on resonant rise, I would like
>>to ask why it is said that resonant charging allows one to suck more
>>power from a NST? I suggest that if that were true, one could set the
>>gap wider than for a non-resonant situation and still have the gap
>>fire at the 2Fmains rate. Any comments?
>>
>>Malcolm
>
>Good question.  I have always assumed this to be the case too.
>Certainly if allowed to build over multiple cycles, the resulting voltage
>will be highest when resonance is met, but I just ran some quick
>simulations with differing capacitances and a 15KV/60mA NST and see some
>surprising things that now make me question this "wisdom".
>
>As expected, if allowed to run over multiple cycles, highest peak voltage
>occurs with a 10.8nF cap (which is precisely mains-resonant at 60Hz).
>But allowing the gap not to fire over multiple half-cycles is something
>that should never be allowed to occur, and therefore is irrelevant.
>
>Now, if I assume the gap is sized to fire exactly once per half-cycle (as
>if a sync RSG or precisely gauged static gap were used) and only look at
>the peak cap voltage after the first half-cycle, it gets interesting.
>The highest cap voltage did not occur with the 10.8nF cap, but with one
>something less than 4nF.  But this is not the whole story either.
>Highest POWER occurs with highest (1/2 CV**2), assuming a constant gap
>firing rate.  The highest POWER occured with between 25-30nF.

Neat isn't it!  It is no coencidence that my cap is now 27.5nF on my 15kV 60mA
neon.  I have not been able to pursue much actual testing of this confuguration
due to problems finding time but it DOES work fine in real life.  As far as I
know, this is the best configuration to pull power out of a single neon.  An
added benifit is that the voltages and currents from the transformer are only a
tiny bit over the transformer's ratings so nother should burn out.  The model
seems to be very acurately predicting the real life behavior of using this very
large cap value.  

>
>These numbers are a rough first pass, because I did not optimize the
>phase of the gap firing to be consistent every mains half-cycle, as would
>be the case if using a sync RSG.  Terry has pointed out that if one does
>use a sync RSG, the optimum cap is 17-20nF, and this does take into
>account adjusting the phase for consistent firing every half-cycle.  I
>see this also if I tweak the simulation phase (somewhat tedious).

My new dual 400MHZ Pentium II helped me with the tweaking here :-))  Trial and
error is the best way I know of to find the best phase dealy value.  Of course,
in actual life, the phase just finds the best place all by itself which agrees
well with what the model shows.

>
>It will be interesting to run a similar simulation with the gap firing
>multiple times per half-cycle, to see which cap size draws highest power.
>Using static gaps, this is a more realistic scenario, as the voltages
>seem to get out of hand if you only allow one big bang per half cycle.  It
>also looks like when using sync RSG's, the caps had better be rated for a
>higher voltage than with a static gap configuration, particularly when
>using lower capacitance values.

In my modeling, the other smaller cap values always deliver less power to the
arc...

>
>Until then, I don't see any evidence of higher power being pulled through
>the use of resonant charging.  Thank you Malcolm, for bringing this up.

        I think the 27.5nF cap size is delivering the highest power I have seen
out of a single 60mA neon so far.  There is some thought that more than 120BPS
"feeds" the streamers better but for maxium power to the arc, the 27.5nF cap
configuration is the best I have seen.

        I don't really think the resonant charging mode is doing the best job. 
The 27.5nF case seems to do much better for me.  Perhaps you will convince
yourself of this too and I woun't be all alone in my beleif that the highest
power transfer point is far away from the resonanat charging point for cap
values.  It is also much safe the the cap and neon...

Cheers,

        Terry

>
>Gary Lau
>Waltham, MA USA