[TCML] Are safety gaps necessary?

["Lau, Gary" <Gary.Lau@xxxxxx>]

I changed the Subj: line to reflect the topic...

Way to stir the mud, Bart!  It's good to make us examine our practices.

I thought about your post quite a bit.  Yes, it does seem hard to justify a separate static safety gap that is in parallel with the main static gap.  I think we've had to do some hand waving and wiggling when we describe to newbies the procedure for separately setting the main and safety gaps.  And I fully agree that a static gap is extremely unlikely to fail in the way that an RSG might.  So I was about to join the heresy and agree that safety gaps appear to be redundant and unnecessary with a static gap.

I slept on it and it dawned on me this morning.  What happens when a streamer strikes the primary?  If one exists, the 3-terminal safety gap fires, channeling the streamer's energy safely to RF ground.  If one didn't have a 3-terminal safety gap, the only path for that streamer energy is through the NST.  I think the NST would be happy that the 3-terminal gap exists!

So I stand by the advice to use a 3-terminal safety gap.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Tuesday, June 17, 2008 8:53 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Chokes and Terry filters
>
> I think all of us are preaching proper gap spacing via NST and gap
> setting (workbench approach) which eliminates the various electrodes
> chosen. Another aspect to consider is that DC typically runs at about
> 1.3 x Cres for his cap size. So he is taking advantage of some resonant
> charging as far as bps is concerned. The static gap still clamps the
> voltage regardless and I agree is the main problem with NST failures.
>
> If I were to weigh in on the filter discussion, I would say the chokes
> are unnecessary with a filter. However, I have even pushed my gap
> setting wide enough to kill an NST even with a Terry filter installed.
> This is when I realized the safety gap was useless due to my gap setting
> and sort of what drives me to stress the margin between safety and main
> gap needs to be large enough to allow the safety gap to work, otherwise,
> it's just a waste of labor and electrodes.
>
> I do push my transformers with what I can get away with. If it fails,
> I'll just fix it or replace it. There are probably a few like me out
> there on that subject. With that in mind, I've even been thinking about
> doing away with the safety gap (my static gap coils only). The reason is
> I have little margin and it's an annoyance when set correctly and
> useless when it's not an annoyance.
>
> The fact is, the probability of a decently built static gap failing is
> slim to none. So, what's the point of the safety gap in that type of system?
>
> Take care,
> Bart
>
> Lau, Gary wrote:
> > Indeed.  I think the reason that DC has been successful in not killing NST's is his
> conservative approach to keeping static gap width small.  That, more than using
> any kind of filter, is the key to long NST life, and that's what we should be
> preaching.  But human nature being what it is, the desire to increase performance
> has us opening the gaps to the max, and that's where Terry filters become useful.
> >
> > Regards, Gary Lau
> > MA, USA

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