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Re: Coil efficiency




From: 	Gomez[SMTP:gomez-at-netherworld-dot-com]
Reply To: 	gomez-at-netherworld-dot-com
Sent: 	Sunday, November 16, 1997 1:24 PM
To: 	Tesla List
Subject: 	Re: Coil efficiency

I wrote:
> >I was recently stunned to learn from one of our customers that a coil which
> >had made 3-4' sparks in Colorado (5300' ASL) was making 5-6' sparks in
> >Indiana (500' ASL).  Humidity was about the same, according to NWS
> >records.

To which Dave Huffman replied:

> Sounds like these numbers are reversed. 

That was my initial reaction- I assure you they are not.

My thinking in the past was that, since lower atmospheric pressure 
equates to more easily ionized air, and a better conductor at extreme 
voltages, one ought to see longer streamers at higher altitude.

But this news from my customers got me to thinking...

Treat the Tesla coil as a high voltage source of finite current capability. 
Treat the discharge terminal (toroid) as a capacitor.  Now, the higher the 
voltage you can charge that capacitor, the longer the streamers you'll get, 
all other factors being equal.  (I know, I know, but let it be- this is just a 
thought experiment)

Treat the atmosphere as a varistor (their behaviors are somewhat 
similar) 

The lower the resistance of the atmosphere (at higher altitudes) the faster 
you'll drain that cap, and in addition, the faster the voltage in the arc itself 
can dissipate.  

If the atmosphere behaves like a bunch of parallel resistances, the arc has 
to travel farther and fartherbefore it will dissipate when those resistances 
are higher.

Treating the atmosphere as distributed capacitances doesn't change this 
model much, since it's still an impedance, although it introduces the 
well-known factor of Fr vs. spark length.

> That or plasma discharge behaves
> differently.

You're speaking of plasma globes, perhaps? I think the two situations are 
not that similar.  In the case of a Tesla coil, one has a great deal more 
"ionizing capability" for surrounding medium.  The air _will_ get ionized 
no matter what, but the question is how long it will take the charge to 
dissipate. In the case of a plasma globe, the voltage is of course, several 
orders of magnitude lower, and one must lower the pressure significantly 
before even an initial ionization wil occur.

This latter is just an off-the-cuff hypothesis, with very little skull sweat 
behind it.  Comments, anyone?

(and yes, the whole thing is somewhat counter-intuitive) 

> mystified! Dave Huffman

You're not the only one!

-Bill "Gomez" Lemieux

-- 
Gomez: certifiable mad scientist, extreme fetishist, fiction dabbler, 
pyrophiliac, technomage, goth, faan, lighting designer, dominant 
pervert, and juggler of labels... http://www-dot-netherworld-dot-com/~gomez