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Re: 60 vs. 30 ma - charging
From: Pete Demoreuille[SMTP:pbd-at-cybernex-dot-net]
Sent: Thursday, June 26, 1997 9:36 PM
To: Tesla List
Subject: Re: 60 vs. 30 ma - charging
John:
the problem with the following explanation is that the you forgot
that tesla coils and transformers use A.C. Ohm's law is not always
correct with a.c. (V != IR) because the voltage and current in a.c.
can be off by a certain degree. ie. that if the phase (think phasors)
is off by 90 degrees, the voltage is zero when the current is maxed out.
On another note:
I have almost finished my first coil:
powered by a 15kV neon -at- 30mA
Caps: two crates of 14 snapple bottles each, each crate rated at 11uF,
which are connected in series to give around 5.5uF of capacitance
One single spark gap made with 2 carriage bolts, housed in a box with an
exhaust fan at one end.
Primary is 12 turns of 1/4 inch copper refrigerator tubing, at a 30
degree
angle to make it ~4in high and 11in radius.
Secondary is ~450 turns of plastic insulated wire, (couldn't find any
enamled,
i am working on it) for a total wrapping length of 21.5in
separation between primary and secondary is 2in
Any suggestions, comments, improvements (I am sure there are many, I am
working on getting some mica for making some real good plate caps, and
making a better, closer secondary, and getting a new transformer)
Any clue how much separation the spark gap should have, and where i
should tap the primary??? Please HELP! I have not a clue.
If you could give a suggestion, that would be greatly appreciated,
but if you could explain how you got the suggestion, that would make
you a god.
Happy Coiling!
Pete Demoreuille
> Skip -
>
> The neon transformer problem is not simple and has confused many coilers.
> I like to look at the neon problem from a loading standpoint. The voltage
> and wattage output will vary depending on the load. However, the current
> wiil be constant only up to a design load then it will quickly reduce to
> zero as the load goes to infinity (open circuit). The voltage and wattage
> will be almost zero at almost zero load.
>
> The design load is Z = V/I where V is the voltage rating of the neon and
> I is the current rating. You will recognize this equation as the one that is
> sometimes (incorrectly) used when selecting the TC primary capacitor size.
>
> To find the voltage at different loads use
>
> V = ZxI where Z is the load ohms and I is the rated current of
> the neon transformer.
>
> For example 12000 volt 30 ma 360 watt neon transformer
>
> If load is 200 Kohms resistor
>
> V = 200 000 x .03 = 6000 volts
> W = V I = 6000 x .03 = 180 watts
>
> The load resistor will get hot!
>
> The voltage (Ohms law) and wattage is a linear relationship with the
> load because the current is constant.
>
> With a capacitor the loading on the neon is an exponential curve. The
> voltage on the cap starts at zero (load almost zero) and builds up to the
> voltage rating of the neon in an exponential curve (vs time) at constant
> current. When the voltage on the cap equals the voltage rating of the neon
> the current reduces to only the losses of the circuit (load is very high
> impedance).
>
> The big question is how does the TC pri cap load the neon when turned on
> and off by the operating spark gap at different breaks per second? Do any
> coilers on the List know how to find the optimum conditions? I have been
> working on this problem for some time but with little success. Keep in mind
> that the loading on the neon should be maximized for best results (an
> iterative solution?).
>
> John Couture