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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.


A truly synchronous rotary gap could be used to solve this problem if 
properly phase adjusted however.  There are still no guarantees 
however since neons are just inherently fragile and seem to live 
short lives in most Tesla service. 

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 custom manufacture such RF chokes as required for Tesla coil use and 
offer them at reasonable prices.  Contact me off list if interested.

rwstephens