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Re: [TCML] Are safety gaps necessary?

Gary, Bart, all.

Given the advice of this list, I have set my safety gap (on a static spark gap system) and when the coil is running I get occasional firing of the safety gap, about 5 or 10 per minute. I was thinking this is all good and it does give me a certain peace of mind. Now given this latest discussion I am starting to think that I should be opening my safety gap out more. BTW I have a strike rail which does get hit occasionaly and it seems that the primary is very inlikely to be hit with the strike rail in place.

Dave Nelson
----- Original Message ----- From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, June 18, 2008 10:05 PM
Subject: [TCML] Are safety gaps necessary?

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

-----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,

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

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