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Re. More SRSG questions
>Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>=20
>>From Terry Fritz:
>>Resonant charged NST systems will develop huge voltages across the primary
>>cap and transformer. This super high voltage will easily destroy the cap
>>and/or transformer. In a static gap system, the gap will ALWAYS fire and
>>save the day. However, rotary gap systems can easily not fire in time to
>>prevent the voltage buildup and BANG!... there goes the transformer.
>>The solution is simple, just have a static safety gap across the
>>transformer or cap. If the rotary decides not to fire, the safety gap will
>>step in and drain the voltage before it reaches destructive levels.
>Agreed (except I would use a SSG across the cap AND the xformer to
>provide a "solid" path to ground for the "too many electrons").
Did you mean across the cap or gap? I would favor the Gap, that way if
it fires, the energy has a useful place to go, into the primary. If the
safety is just across the Cap, it will see some frightful currents (no
inductors to limit it) and do nothing useful. Clamping-wise, it makes no
difference, the cap and gap see the same voltages.
>However, this leads me back to my old question: Can I build a RSG
>that is in sync with the mains, but has a higher break rate? I do NOT
>mean 800+ bps, nor do I mean crooked (being non sync) values like
>320/384bps (50/60Hz). I mean "x" times the mains frequency, like
>240(200) or 360(300) bps for 60/50Hz. I am stuck with neons for the
>time. I can understand why NSTs can die using a async RSG. By using
>a "high speed" (relative) sync RSG with bps rates mentioned above, I
>could get away with a smaller cap. The MRC (mains reso cap) for my
>final setup would be around 254nF (for 4500VA). That is way too big.
>Using a sync RSG that fires 2 per half cycle (instead of once) I could
>half my needed cap size. As static gap (more or less) fire at will and
>have break rates higher than 2*Fmains, I cant see any reason why
>a sync RSG wouldnt work. The stress shouldnt be any larger than
>using a static gap and the higher number of break rates should help
>protect the cap from overvolting, because it has the possibilty to
>discharge more often. It would seem such a setup would be much
>safer for the xformer and cap than a resonant charged and 100/120
>bps discharged setup. Of course, SSGs (safety spark gaps) should
>still be incorperated. So, can I do this and will it be safe for my NSTs
>and caps?!? Any ideas and comments are welcome.
>
>Pondering in germany,
>Reinhard
I have performed some PSpice simulations, looking for the best cap values
to use with my 15kV/60mA NST. I simulated sync gaps, both at 120 and
240BPS. For reference, using static gaps, best case was a 9nF cap, power
throughput dependant on gap width, 534 Watts with a 25KV static gap. A
mains-resonant cap would have been 10.8nF.
For the 120BPS case, best case was with about 20nF, charging up to 23.17KV,
or about 644 Watts throughput. Timing was adjusted to fire at the peak
charging voltage.
For the 240BPS case, best case was with about 8nF, charging up to 24.30KV,
or about 567 Watts throughput. Timing was adjusted to make the two bangs
per mains half-cycle equal in size.
So your reasoning about using a 200BPS sync RSG to allow the use of a
smaller cap seems valid, although there will be some loss of throughput.
Regards, Gary Lau
Waltham, MA USA