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Re: Tesla Coil (No tank circuit or Cap's required)



Tesla List wrote:
> 
> Original Poster: fprice3 <fprice3-at-acnet-dot-net>
> 
> BRAVO!!!
> 
> A very intelligent solution to an apparently difficult problem.
> 
> Grounded outside conductor?
> 
> Try a rectifier or a full wave voltage doubler next???
> 
> Would a co-axial cable do the job?  Has anybody data on High Voltage
> capability of Coax?


RG-8 or RG-213 (roughly 0.4 inch in diameter) is nominally 5 kVAC RMS in
transmitter duty. This actually allows for a load mismatch of (i think)
3:1 which means that at some points the voltage will be markedly higher.
In practice, I have run 40 kV through RG-8 without any problems. I use
the very common modified PL-259/SO-239 (UHF connector) as HV connectors.
(i.e. you punch out the center and replace it with a piece of acrylic or
PE rod a few inches long and a banana plug).

The dielectric is about .2 inches thick. However, the field strength
isn't uniform: stronger in the middle: E=V/ (R * ln(b/a))
(for RG-8 b = .285, a =.076). This reduces to E (volts per inch) = 10 *
V, so, for 40 kV, you'd be putting about 400 V/mil on the dielectric. PE
has a dielectric strength around 800 V/mil, so this is probably safe.

Of course, if you use that ratty old piece of surplus coax that you
found in the water filled barrell at the junk yard........

I might add that having the shield grounded makes the field on the
dielectric uniform, which improves the dielectric strength of the cable,
as well as providing a safety factor.

HOWEVER, do not neglect the transmission line effects. If you run your
power down this long cable and then have a spark gap at the end, you
will have made a very effective pulse forming line, which, depending on
your pulse rates, cap sizes,etc,etc. can cause very high peak voltages
as the wavefront reflects back and forth down the line.

-- 
Jim Lux                               Jet Propulsion Laboratory
ofc: 818/354-2075     114-B16         Mail Stop 161-213
lab: 818/354-2954     161-110         4800 Oak Grove Drive
fax: 818/393-6875                     Pasadena CA 91109