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Rotaries and Neons (fwd)
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From: Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: Sunday, August 09, 1998 5:07 PM
To: Tesla List
Subject: Re: Rotaries and Neons (fwd)
Hi Gary,
> Date: Fri, 7 Aug 98 10:14:53 EDT
> From: Gary Lau 07-Aug-1998 0935 <lau-at-hdecad.ENET.dec-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Rotaries and Neons (fwd)
>
> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> >To: Tesla List <tesla-at-pupman-dot-com>
> >Subject: Re: Rotaries and Neons (fwd)
> >
> >Hi Gary,
> > I should have elaborated a bit:
> >
> >> Date: Wed, 5 Aug 98 08:44:14 EDT
> >> From: Gary Lau 05-Aug-1998 0817 <lau-at-hdecad.ENET.dec-dot-com>
> >> To: tesla-at-pupman-dot-com
> >> Subject: Rotaries and Neons (fwd)
> >>
> >> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> >> >To: tesla-at-pupman-dot-com
> >> >Subject: Rotaries and Neons
> >> >
> >> >Terry, Gary Lau and all,
> >> > I'm seeking an opinion here: if one uses a
> >> >good RC filter with a NST, is there any remaining hurdle to using an
> >> >async rotary gap?
> >> >
> >> >Malcolm
> >>
> >> As I understand it, the reason that async rotary gaps are not recommended
> >> for use with neons is not related to filterable high frequency transients.
> >> The same kinds of high voltage, high frequency resonances should occur
> >> regardless of sync or async, or static or rotary gaps.
> >>
> >> The problem with async RSG's and NST's has due to the fact that mains
> >> resonance between the NST and primary cap will exceed the NST's breakdown
> >> voltage if and when a mains voltage peak does not coincide with a gap
> >> presentation. Using a sync RSG guarantees this cannot happen. Pole pigs
> >> are more robust and can survive a mains ring-up.
> >
> >I quite understand this and for a long time have advocated planting a
> >static gap firmly across the rotary to catch misses. If this is done,
> >do you still see any objections?
> >
> >Thanks,
> >Malcolm
>
> Hi Malcolm:
>
> I was sure you already knew this and I posted my reply largely for the
> benefit of list members that may not be aware of these subtle hazards,
> thanks for clarifying.
>
> As you suggest, a static gap shunt across an async RSG should protect
> against mains-resonance peaks. It may however be counterproductive in
> that it will limit Vpri to the same value as if you were using just the
> static gap.
>
> As to whether the combination of the static shunt and RC filters will
> eliminate all NST hazards, I wouldn't bet on it, ever. It wasn't long
> ago that most of us thought the main hazard was at the tank Fres and we
> strived to filter that out. Now we know about the Igap zero-crossing
> bursts. Who knows what will be discovered tomorrow? It's been suggested
> that NST's were never designed to even run at their rated voltages, that
> neon tubes clamp the output voltage to something far less, so it could
> even be that running an NST open circuit with nothing attached is bad for
> it!
>
> Additionally, the question you posed as to why safety gaps fire
> differently than the main gaps has yet to be definatively answered.
> There is the strong possibility that some unrecognized mechanism exists
> to boost the NST output voltage enough to fire the safety gaps, despite
> RC filters between the safety and main gaps. I could speculate and
> simulate until the cows come home, but unfortunately lack the test
> equipment to observe this.
>
> Regards, Gary
Thanks for the wise words. I am planning to scope this to see.
Perhaps I should run a NST o/c for a day to see whether it will die.
I hope it doesn't but if it does, I guess all bets are off.
Regards,
Malcolm