Re: The worlds Largest Coil

To: tesla-at-pupman-dot-com
Subject: Re: The worlds Largest Coil
From: "Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 09 Mar 2000 13:53:04 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Some more calculations..

Assume a spherical top load 10 m in radius (32.5 ft, 390 inches) = 1100pF
Assume a secondary 20 ft in diameter and 100 ft high with windings every 3
inches = 166 mH
Self C of secondary is another 500 pF

Resonant frequency is about 10 kHz..
At this frequency, the impedance of the secondary is about 10.4 Kohm.

Say we want the Q of the secondary system to be at least 10.. The wire
resistance needs to be <1 K.
There is about 25000 ft of wire in the secondary, so we want our wire to be
<40 ohms per thousand feet.. or AWG 24.   In reality, you'd probably want a
design Q of 100, so you'd want <4 ohms/thousand feet, or AWG 14...  This is
readily available in long lengths at a reasonable price.  Perhaps you'd go
to #10 or #12.

Another idea is to make the resonant frequency some nice multiple of 720
hertz, so that you can use resonant charging from a 3 phase 60Hz supply.
720Hz is figured based on positive and negative peaks of each phase, with
two feed transformers, one Wye and the other Delta (essentially a 12 pulse
rectifier).

It seems a bit tough to get the resonant frequency down that low (you'd have
to have a LOT more turns on the coil) (frequency goes as sqrt(L), and L goes
as N^2, with the net result that you'd have to have 10 times the turns)

However, make the Q high enough, and don't pump every cycle of the
resonance.  If the Q were 100 (say), and the resonant frequency were set to
7200 Hz, you would put a power pulse in every 10th cycle.  The maximum
energy in the system would then be 10 times the pump energy.

With the 10 meter diameter top load, the maximum stored energy would be
1000pF * (10*3MV)^2/2 = 448 kJ. so your pump energy (per pulse) would be
45kJ per pulse.  At 720 pulses/second, the power draw would be about  32MW.
The secondary winding would be dissipating that much heat, by the way.

It would be a relatively feeble lightning stroke too, at 15 kJ/meter.  (But
still mighty impressive...)


How much would this cost?  A bunch, but mostly in structural components..