[TCML] Are safety gaps necessary?

[bartb]

Hi David,

The TCML is place for advice and also for general discussion. My safety 
gap comments are only a discussion and I don't advise anyone to consider 
increasing the safety gap unless it's really firing way too often and 
your certain the main gap is set properly. And I certainly don't advise 
removing it, but it's just a consideration for myself I'm thinking about 
(and only thinking about at this point). A better alternative for most 
is to actually reduce the main gap a little.

As far as strike rails, I have had strike rail hits and primary hits 
using them. I experimented long ago just removing the strike rail and 
although I did have a few primary hits, there were far less. This was a 
big 13" dia. coil. Spark control and power is real consideration here. 
If there's just enough power to reach the primary, then you can get 
quite a few hits. Power needs to be high enough to send those sparks out 
and away and a nice large and wide toroid helps (as does a nice compact 
primary). The ring can be a target of sorts. But none of this is written 
in stone.

My personal feeling is that there may be coils better off with a strike 
ring and coils better off without them. Field control, power, bps, 
primary, height, etc.. all play a role in the sparks character. The idea 
is to minimize primary strikes. One needs to experiment with their own 
system to find out what minimizes primary hits. If you find more hits to 
the primary without a strike ring, then add a little more power, change 
bps, etc.. experimenting to reduce them to almost nothing. Then try the 
strike ring again and compare.

Although I may state my experience, I won't advise anyone to simply 
remove a strike ring (at least not these days). My advice is that on 
this subject, coilers should certainly experiment with field control 
changing power, bps, toroid heights, size, etc.. Size is difficult 
unless you have a few toroids around, but the rest can be altered 
easily. These things affect the sparks characteristics (length, time, 
direction, dissipation, etc.). And they should do what works best for 
their coil.

Take care,
Bart

David Nelson wrote:
> 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 at hp.com>
> To: "Tesla Coil Mailing List" <tesla at pupman.com>
> 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
> MA, USA
>
>> -----Original Message-----
>> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] 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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