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Re: An Interesting Problem (fwd)



---------- Forwarded message ----------
Date: Thu, 16 Oct 1997 10:59:55 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: An Interesting Problem    

Hi John,

> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: An Interesting Problem   
> 
> In a message dated 97-10-15 16:09:38 EDT, you write:
> 
> << It didn't have any particular preference for which side of the toroid 
> > it threw sparks from. Perhaps I'm misunderstanding what you're saying.
> > How can ions floating around the toroid affect gap behaviour like 
> > this?
>  
> > Malcolm
>   >>
> Malcolm,
> If I understand your original observation, your gap kept firing steady,
> but the toroid sparked intermittently, let me know if I'm wrong.

I'm afraid that's wrong. Output voltage was just high enough to allow 
breakout sometimes but when it did establish a good arc, the gap 
would stop firing dead in its tracks and stay that way for an 
indeterminate time ranging from perhaps 1/2 second to several 
seconds.  OK, I had a think about it after Fr. McGahee's post of 
yesterday and I have a likely scenario. 
     Suppose the gap is set so that it is marginal as to whether it 
can fire or not and suppose that a transient generated at switchon
allows it to fire. Then if it is marginally set and bearing in mind 
that the transformer has very little leakage inductance compared to a 
neon, the next gap fire is only going to fire _guaranteed_ if there 
is some energy stored in that leakage inductance because of the 
marginal gap setting. The amount stored in the leakage inductance 
depends heavily on gap conduction time (i.e. the time the gap shorts 
the transformer for).  With a heavy secondary discharge, conduction 
time is _greatly_ shortened compared with a short airstreamer or no 
breakout at all so little energy is stored in the transformer so 
there is now no guarantee that the gap will conduct on the next half 
cycle of the mains.
      The real problem was that I had to set the gap this marginal 
because Csec is now a lot higher which makes Vout a lot lower which 
in turn means that setting the gap closer allows it to fire 
steadily alright but no output streamer. Adding a bump to the 
terminal degraded output length significantly but did enable more 
regular gap firing. Messy at best.
     This is the best explanation I can come up with right now. There 
are two basic problems with this coil: firstly the transformer which 
has a relatively low output voltage and little leakage inductance 
and secondly, primary energy is now almost too low for Csec and the 
terminal shape. I think another couple of kilovolts on the primary 
side would make a world of difference. I am entertaining the idea of 
building a triggered gap for this coil to overcome the low voltage 
problem. It would be difficult to machine a rotary to have electrodes 
close enough to deal with the problem. I can't do any better voltage-
wise with the transformer in question
     Gap behaviour was its usual brighter self with no breakout.

?
Malcolm