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Re: Ronnnie's Coil
In a message dated 97-02-14 02:04:39 EST, you write:
<< Ed,
Thanks for the help. So far this is all I know about my system.
It is running off a 6 kv 30ma transformer. there are 983 truns of 24 ga.
magnet wire on a sanded and sealed 4" pve drain pipe (actually
circumference is 13 7/16 " which would make the diameter about 4.277 ")
. The primary is made of 10 ga. house wire wound on vertical dowels
forming a helix with a diameter of 10 ". I tried making a 4" x 20"
toroid to place on top but when I did I could not get the system to
spark out at all, thus for the science fair I replaced the toroid with a
aluminum pie pan. As for the capacitance of the snapple bottles, I am
not sure how to calculate it and I do not think I have the equipment to
test for it.
One thing I was curious about, when I ran it for the science
fair, many times it would not run from the start, I would plug it in and
the spark gap would fire a few times and then the thing would just hum.
In order to get it to work I had to plug it in and unplug it several
times and eventually it would get going. Is my safety gap arcing over
or something.
Anyway thanks again for your help I really appreciate it.
Adios
Ronnie
>>
Ronnie,
Here is the formula for salt water capacitors. It was originally posted I
think by Richard Quick in the Tesla Math Formulary:
EQUATION 2: LEYDEN JAR or SALT WATER TYPE CAPACITORS (jar/bottle type)
2
C = .0884 k ( pi r + 2 pi r l )
------------------------------
1,000,000 t
C = Capacitance in microfarads
k = dielectric strength
r = jar radius in centimeters
l = height of the jar portion used (in centimeters)
t = thickness of the jar wall in centimeters
pi = 3.141592654
2
r = r x r (radius squared)
I have known folks to say they get about 700 pf from 12 ounce beer bottle
caps. You might want to try calculating yours & see what you get. You could
measure them by placing a known capacitor in series with one bottle cap and
use a small ac voltage or signal generator to apply voltage across them in
series. When both caps are equal in value, you will have one half the total
voltage across each cap. How many bottles do you have again?
As to not starting, your gaps must be set up just a little too wide. 6 kv is
kind of low for a Tesla coil. Maybe you can find a 9 kv or 12 kv 30 ma
transformer. If the safety gaps were firing, you would be able to see that.
The safety gaps should normally be set up wider than the main primary gap.
How many turns in the primary and what is the spacing between turns? I
apologize if you have already posted this. If you did, I can't find it.
The 4 x 20" toroid not breaking out is another indication of not enough input
voltage (and possibly being way out of tune).
Back an hour later: I have done some calculations on you coil. Your
secondary should have about 22.9" of windings. It should be about 18.5 mh,
with 8.9 pf of self capacitance. Allowing 5 pf for your pie plates, the
loaded resonant frequency should be about 314 khz.
If your primary is 10 turns of #10 wire, 10" diameter with .25" between
windings (I made some assumptions here), the inductance would be 32
microheneries. This will require 8,000 pf of tank capacitance with the
primary tapped out at turn # 10. At about 700 pf per bottle, you need 12 of
these bottles in parallel. With your 20" toroid, assuming about 15 pf of
effective capacitance, you need 14,000 pr ( .014 mfd) which would be 20 salt
water cap bottles in parallel.
In order to reduce the number of bottles required, you might consider winding
a new flat pancake primary. Using the same # 10 wire, you might go with 14
turns at .35" spacing. This would be 64 microheneries and would require only
6 bottles with the pie plate toroid and 10 bottles with the 20" toroid
(assuming 700 pf / bottle).
Ed Sonderman