Coil efficiency

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Coil efficiency
From: Tesla List <tesla-at-stic-dot-net>
Date: Sat, 8 Nov 1997 23:42:42 -0600
Approved: tesla-at-stic-dot-net

From: 	ntesla-at-ntesla.csd.sc.edu[SMTP:ntesla-at-ntesla.csd.sc.edu]
Sent: 	Saturday, November 08, 1997 11:09 AM
To: 	tesla-at-pupman-dot-com
Cc: 	ntesla-at-ntesla.csd.sc.edu
Subject: 	Coil efficiency

[snip]
>>If you are going to use TC efficiency correctly
>>you should use controlled spark lengths or leave out the reference to
>>efficiencies. A Figure of Merit could be used as this can have any specified
>>meaning.  
>>
>>  Comments welcomed.
>>
>>  John Couture


>John,
>
>I never refer to a tesla coils "energy efficiency" under any circumstance as
>it is a meaningless figure to me. (even as an electronics engineer)  I
>figure a tube coil might be a spark gap here or at least have a good shot
at it.
>
>I build coils for spark and spark alone.  This said, true tesla coil
>efficiency is judged by energy in versus spark length out.
>
>Richard Hull, TCBOR

I find output spark-length to be meaningless as anything other than a "wow"
factor, since spark length is directly related to oscillator-frequency,
humidity, atmospheric pressure and air-temperature. 

Make a plasma-globe and try all kinds of different gas pressures at varying
frequencies, voltages and currents, and the factors become evident as
discharge-length and formation. For example, by using a driver 15kV -at-
20kHz, and varying the input current to the driver, discharges range from
short sparks, to forked lightning-like discharges, to thick plasma-fingers.
The *exact same* effects are manifested by leaving the current constant and
varying the gas pressure. If I leave the the current and pressure constant,
I get the *exact same* effects just by varying the driver frequency. So,
unless a coil's output spark-length is measured in a controlled atmosphere,
the measurements are meaningless except for that particular coil, in that
particular place. Make the measurements in Arizona in the summer, and then
bring it here to SC, and there's no way the coil will give the same output.
And I highly doubt that coil "efficiencies" are going to change based
*only* on geographic location. ;) 

The implication to me is that there must be an optimum coil frequency,
based on air-pressure, temperature and humidity that will allow the
greatest spark-length without regard to power levels at all. No sense in
doing measurements in a lab if the results cannot be broadly generalized.
Those measurments would rapidly approach zero as far as statistical
significance is concerned :)

Dan
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