neon trannie loading?

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: neon trannie loading?
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 21 Jun 1998 23:55:29 -0500
Approved: tesla-at-stic-dot-net

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From:  Bill the arcstarter [SMTP:arcstarter-at-hotmail-dot-com]
Sent:  Sunday, June 21, 1998 3:36 PM
To:  corr-at-enid-dot-com; tesla-at-pupman-dot-com
Subject:  Re: neon trannie loading?

Hi Jeff, coilers,
 Jeff wrote:
>I got a flyer here from Franceformer saying that
>neon transformers should be loaded to 75% to 85%
>of the designated max. current.  Ex : a 30ma neon 
>should be loaded to 24ma or 25ma.  If this was true,
>would this not explain why tesla coils kill neons
>fast?

A neon sign transformer (NST)  can be short-circuit all day long w/o any 
problems whatsoever.  The neon tubes (which is what *some* people power 
with a NST) will only drop about a couple of hundred volts once they've 
ignited.  The full 15KV (or whatever) is only required for the initial 
ignition.

I would doubt that Franceformer's loading information would be of any 
value to coilers since a tesla coil is hardly a steady drain! 

>(charging up the cap would be like a temporary
>short, pulling much more than 25ma, right?)

If you slam a fully discharged cap across a neon - it will only draw an 
instantaneous current to the tune of 30 ma (or whatever the NST rating 
plate lists).  (I am talking 'instantaneous' here - not steady state 
(resonant rise etc).)

However, I think you might be on the right track here.  I've done some 
experiments in single shot mode which show that usually the primary 
capacitor is left with a substantial residual voltage (of random 
polarity) once the gap quenches out.

So now the situation is different as you now have the capacitor (charged 
to ?? thousand volts of possibly reverse polarity from the neon) pulling 
a current through the NST windings in conjunction with the 
(magnetically-limited) 30 ma, etc. 

I suspect this might be one damage mechanism.  Perhaps the large bulk 
inductance of the NST limits the reverse current caused by the 
(reverse-charged) capacitor??? (playing devil's advocate against myself 
is always uncomfortable...)

>Could this also be why resisitors in series with the
>chokes help save neons?  Since adding resistors, I
>have not ever lost a neon, and was getting very good
>sparks.

I bet what is happening here is that the resistors, in conjunction with 
the parasitic capacitance (and substantial bulk inductance) within the 
neon are acting as a sort of low pass filter - suppressing some of the 
higher frequency "backlashes" and limiting the instantaneous currents 
which would otherwise kill the neon.  But I might be wrong. :)

Any thoughts?  Comments invited!

-Bill (arcstarter)