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Tesla Coils

 WL> I've been playing around trying build a Tesla coil 
 WL> with no luck. 

stuff deleted..,

 WL> If I was to build the above coil how would I work out the coil 
 WL> length's and thickness etc... ? 

 BB> The name of the game is resonance. Many years ago I built a coil 
 BB> that was about 5 ft high and 2 1/2 in. diameter. It resonated about 
 BB> 500KHz. 

Ugggh. Very poor design. Certainly not a design you would want to pass
along or recommend. I believe this design results from mathmatical 
"radio theory", as it most certainly cannot stand up to experimental 
performance tests against other resonator geometries. The best resonating 
coil is short and squat compared to the "candlesticks" of the 1960s and 
1970s. The secondary coil should be wound with #22 gauge, or larger, 
enamel covered magnet wire with between 800 - 1000 turns total. The 
aspect ratio (height to width ratio of the coil form) should be:
       4 inch diameter coil form, 5:1 aspect ratio; 
       6 inch diameter coil form, 4:1 aspect ratio; 
       8 inch and larger diameter coil forms, 3:1 aspect ratio.

I would not wind a coil under 4 inches in diameter.
 
 BB> The coil itself has inherent capacitance and the inductance 
 BB> can be determined from formulas found in elementary texts. 

But all of this is completely unnecessary if the simple rules of thumb 
are followed. My data is reproducible, and has been experimentally
verified.

 BB> Keep in mind that this device is a transmitter 

ugggh. Incorrect statement. The power processed by a sparking Tesla
coil is consumed, not radiated. The primary/secondary are inductively
coupled, so a very strong magnetic field exists locally around the 
coil, but the tank circuit is not radiating. The secondary is trans-
forming and resonating from energy exchanged by the primary/secondary 
field flux. The secondary coil resonates to produce a high voltage, and 
the energy is consumed producing light, sound, and chemical changes in 
the air (production of ozone and nitrogen oxides).

 BB> and may be illegal 

Tesla coils are perfectly legal as long as the base of the secondary
is properly grounded, the coil is in resonate tune, and sparking.

 BB> and will no doubt cause RFI in your neighborhood. 

I fire my coil with 10 kVA input. The calculated peak power is around
10 megawatts. The spark gaps and tank circuit require minimal RF and
spark shielding, mainly to keep the coil from striking back to the
oscillator, power supply, and utility circuits. This coil will light
unconnected (to anything) fluorescent bulbs 25 feet away. Yet the 
neighbors have never complained about RFI, and I have gone over
and checked with them while an assistant manned the coil controls.
Fifty feet away my family detects a slight bit of snow on the TV
that is fed 120v from one side of the 240v line that powers the coil.

Mathmatically this can be explained by transmission line theory, 
and the radiating properties of damped wave trains (as opposed to 
continuous waves). But any coiler worth his salt can experimentally 
verify this with various receivers and inductive pickup coils. 
Sparking Tesla coils simply do not transmit.  

 BB> Also, RF burns are nasty. 

I won't argue there. While standing in the inductive field flux of
a large Tesla coil I have received painful RF burns in the groin area
from loose change in my pockets. Now I always remove any conductors,
especially rings, watches, and change, from my person before powering 
up any coil. I have also had all of the magnetic strips on my ATM and
credit cards in my wallet erased...

Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12