Re: Question?

On Wed, 09 Dec 1998 11:49:50 -0700 in the Tesla List
Scott MacGregor <smacgregor-at-aasp-dot-net> wrote:

>To the list,
>Does anyone know the formula for calculating the reverse voltage
>and current levels delivered from a MULTI-LAYER coil after a
>steady state DC voltage applied to the coil is suddenly
>interrupted? (if the coil is able to discharge through a spark
>gap) I hope I'm stating this properly.

Yes Scott, the effect you are describing was first observed by
Michael Faraday and has been described as the counter EMF where
EMF stands for Electro - Motive - Force. The formula for
calculating the counter EMF is:

  V = L x I/t

Where V is the counter EMF, L is the inductance in Henries, I is
the current in amps and t is the time it takes for the field within
the coil to collapse. This effect was first used to make
"shocker coils" in the last century a very large inductor was
connected to a buzzer like gap as was also found on induction coils
and when the shocker coil was running it would turn a few volts
from a battery supply into several hundred to several thousand volts
which would shock someone holding the output electrodes. As for it's
application to the Tesla coil, it has been done and they are referred to
as "kicker coil" driven Tesla coils. This type of coil was generally low
in wattage although it has been applied to some sizable coils as
described in Thomas Stanley Curtis's book;
"High Frequency Apparatus" 1916 (reprinted by Lindsay Publications
1988)in chapter VIII "Kicking Coil Apparatus". The most common
application of the "kicker coil" was in the "Violet-ray" apparatus
and the hand held vacuum testers both having identical circuits,
an example of which is below.
                                      ) S
                 VG ____  _|_         )
                      | | ___C        )P
                     #( |__|__________)
                   C #(    |
                   O #(    |
                   I #(    |
                   L #(    |
                      |    |
                     AC or DC

You have an iron core coil connected at one side of it's windings
to the line. The other side of the coil connects to a vibrating
armature almost identical to those found on the old induction
coils. The stationary contact of the interrupter is connected to
the Tesla coil primary P, the other side of the primary is
connected to the Tesla coil secondary S. the primary also connects
to the moving contact of the interrupter and the capacitor C is
across the vibrating spark gap VG. There should be an adjusting
screw that pushes the moving armature of the vibrating spark gap
closer to or further away from the stationary contact.

I personally feel this type of circuit shows the most promise for
replacing the gradually vanishing neon sign transformer and offers
the best solution for those living in parts of the world where high
voltage transformers are next to impossible to get, after all it's a lot
easier to build a single large coil inductor instead of having to build a
two coil transformer. The only down fall I see in this type of design is
that there is a direct path through the secondary back to the A.C. mains
and consequently there is always a serious lethal shock potential.

                       Alfred A. Skrocki
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