Re: [TCML] Are safety gaps necessary?

[bartb <bartb@xxxxxxxxxxxxxxxx>]

Thanks Gary for sleeping on it. In the case of a strike I had not 
considered. In the event of a primary strike, there is the primary to RF 
ground and there is the MOV's across the Terry Filter (and there is the 
NST itself). I think the MOV's would save the NST. But, how short would 
the life of the MOV's be? I think maybe it's not that big a deal if a 
Terry Filter is involved. I think I should test it out. This is one of 
those things that requires good old "strike the primary 1000 times and 
see what occurs". Maybe a small on the primary pointing up at the toroid 
would suffice for a lot of primary strikes. My little 4.5" coil is 
perfect for this test, but I stuffed it away for the time being.

That will have to wait until my SISG coil is tested out. But, I still 
think a safety gap may not be necessary regardless of primary strikes. 
Can't prove it and until then I continue to use a 3-terminal safety gap.

Take care,
Bart

Lau, Gary wrote:
> 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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