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Re: spark gaps

At 11:08 PM 10/17/96 -0600, you wrote:
>>From rwstephens-at-ptbo.igs-dot-netThu Oct 17 22:48:11 1996
>Date: Thu, 17 Oct 1996 16:01:10 -0500
>From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
>To: tesla-at-pupman-dot-com
>Subject: Re: spark gaps
>
>>>From mhammer-at-midwest-dot-netWed Oct 16 23:00:56 1996
>>Date: Wed, 16 Oct 1996 19:39:16 -0500 (CDT)
>>From: Mike Hammer <mhammer-at-midwest-dot-net>
>>To: tesla-at-pupman-dot-com
>>Subject: spark gaps
>
>>Hello all,
>
><snip>
>
>>Questions.
>
><snip> 
>
>>4. The message I get from the list archives is that rotary gaps are not 
>>   for neons. The message is loud and clear that using a rotary on a neon
>>   is inviting transformer failure. Why? What is it that promotes a failure?
>>   I'm not likely to build a rotary anytime soon but would like to know just 
>>   the same.
>
>>Any input appreciated.
>
>>Mike Hammer
>>mhammer-at-midwest-dot-net
>
>Mike,
>
>Re your rotary gap and neons question.  Because of the inherently 
>high secondary inductance of a typical neon xfmer when used with 
>power matched capacitor sizes for tesla coils the resultant circuit often 
>operates at some level of 60 Hz resonant charging.  It is not 
>uncommon to see over 20 kilovolts appear across the output of a much 
>lower nameplate rated neon.  When you use a static gap system it inherently
>acts as a safety clamp, limiting the overvoltage on the transformer because
the 
>static gap is always physically present across the transformer.  When 
>one exchanges the static gap for a rotary, now you have a gap system 
>that may not have its contacts anywhere near closed at the same time 
>that the 60 Hz waveform on the neon secondary is experiencing a 
>voltage peak.  In this case the neon becomes grossly overvoltaged and 
>the smoke that is bottled up inside which it needs to work properly, escapes.

OK, that makes perfect sense. I just don't think I ever saw it explained
before.


>
>I advocate the use of rather high value air core RF chokes in series with the
>neon secondary leads.  Before going to them I lost every neon (several) that I
>played with on the bench.  Since 'discovering' the benefit of them I
haven't lost 
>a single transformer.  When I say high value I'm talking in the order 
>of 150-500 mH.  I also employ a single (not grounded center tap) 
>needle point safety gap directly across the neon output terminals 
>adjusted for occasional firing.


I have been using a close spaced safety gap since the beginning. I have not yet
lost a single neon. At first I used only a safety gap. When a kickback would
occur it sometimes sounded like a rifle shot. I added a pair of toroidal
chokes of approximately
4 mh each. Now the kickbacks are a soft pop and much less frequent.




>I custom manufacture such RF chokes as required for Tesla coil use and 
>offer them at reasonable prices.  Contact me off list if interested.
>
>rwstephens
>
>
Mike Hammer
mhammer-at-midwest-dot-net