[Prev][Next][Index][Thread]

Re: Coil efficiency


From: 	Bert Hickman[SMTP:bert.hickman-at-aquila-dot-com]
Reply To: 	bert.hickman-at-aquila-dot-com
Sent: 	Monday, November 17, 1997 8:49 AM
To: 	Tesla List
Subject: 	Re: Coil efficiency

Tesla List wrote:
> 
> 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

Gomez and all,

Sounds like the primary spark gap is breaking down at a lower voltage,
reducing the energy available per "bang" and, as a result, the coil
output voltage. If you readjusted the gaps to get the same voltage at
the top of the coil, the streamers would, in fact, be significantly
longer. BTW, this was a real problem for early rotary spark-gap driven
radar systems in airplanes...

-- Bert --

-- Bert --