Re: HELP ME PLEASE!

To: tesla-at-pupman-dot-com
Subject: Re: HELP ME PLEASE!
From: Bert Hickman <bert.hickman-at-aquila-dot-com>
Date: Wed, 01 Jan 1997 09:39:28 -0800
Subscriber: bert.hickman-at-aquila-dot-com Wed Jan 1 21:37:51 1997
Tesla List wrote:
> 
> Subscriber: falco-at-fuwutai.wh.lucent-dot-com Tue Dec 31 23:03:51 1996
> Date: 31 Dec 96 14:33:00 -0500
> From: Steven A Falco +1 201 386 4865 <falco-at-fuwutai.wh.lucent-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: HELP ME PLEASE!
> 
> > Make sure your spark gaps are connected across your neon transforrmer
> > outputs. The SW cap bank should be connected in series with your TC
> > primary winding.
> 
> This is a question I have had as well.  I presently have my (plexiglas
> plate) capacitor across my neon, and my spark gap is in series with my
> primary.  But you seem to be advocating a different schematic.  Is your
> recommendation unique to SW caps or should everyone have the gap across
> the neon feeding a series cap/primary?  Seems wrong to put a dead short on
> the neon.  I'd like to understand the tradeoffs before I upgrade my coil
> rather than after :-).
> 
> My intuition told me that having the cap across the neon would be preferable,
> because it would help protect the neon from HW spikes.  The cap should act
> like a very low impedence at high frequencies.  Consequently, I presently
> have no other RFI filtering than the main cap.  Comments, please?
> 
>         Steve

Steve,

This is one of those cases where "intuition" will lead you astray. The
problem with placing the cap across the neon is that once the gap fires,
high voltage RF is now directly placed across the neon outputs. The fine
windings on your neon have significant inter-turn and inter-layer
capacitance. While this is not a problem at 60 Hz, it is a very serious
one at 100 + kHz. The high voltage RF causes significant heating of the
insulation and large amounts of corona. In a brief time, these will
cause the neon's output to decline (as short circuits form between
layers), and finally complete failure of the neon. 

Placing the gap across the neon shunts most of the high voltage RF
during the time that the heaviest amount is present. However, even in
this case, once the gap is extinguished, some RF is back-fed from the
secondary to the primary, and can appear across the neon, eventually
killing it - it'll just take a little longer. Some coilers also employ
RL or RLC filters and safety gaps to provide a little more protection
for the neon.

The bottom line: If you use neons, find a cheap source of replacements -
you'll need them sooner or later! :^)

Safe coilin' to you!

-- Bert --