Re: help with a different type of coil

From: 	Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Reply To: 	alfred.skrocki-at-cybernetworking-dot-com
Sent: 	Friday, July 25, 1997 11:51 AM
To: 	Tesla List
Subject: 	Re: help with a different type of coil

On Wednesday, July 02, 1997 9:48 AM Rodney Davies
[SMTP:rgd872-at-anu.edu.au] wrote;

> > Right now, I'm trying to build a tesla coil, the thing is, it isn't like
> > any of the ones (as far as I can tell) that are discussed about in this
> > group or are frequently seen on the web.  We used one in my Physics
> > class and my teacher said it was a tesla coil, but I didn't recognize it
> > as one.  Well, it is rather old, but I will describe it.  It has an
> > electromagnetic switch, that once it opens, it breaks its own circuit
> > (the power to the magnet) and thus closes again and this cycle repeats
> > very fast.  The switch also breaks the current of a separate circuit
> > consisting of a power supply, a coil, and a spark gap.  My teacher said
> > that breaking the circuit in the coil generates high voldages and the
> > sparks to jump the gap.  The coil he used was powered by a low
> > voltage/current dc power supply.  The coil is iron core, my teacher said
> > it is better for inductance.  I'm not to clear on the inductance stuff.
> What you've described is an induction coil - another Tesla invention!
     Rodney, Dr. Tesla invented many great things but the induction 
coil was not one of them!

> It works similar to a tesla coil, but on DC. (yes, DC TC's do exist too!),
> but you should be able to slide the outer-coil off.

     The operating priniple of an induction coil has NOTHING 
WHAT-SO-EVER in common with a Tesla coil! An induction oil is 
essentialy an open core transformer driven by pulsating DC from the 
interuptor in it's primary circuit, it's ratio of transformation is 
in direct relation to the primary to secondary turns ratio. A Tesla 
coil operates by transfering energy between to differing capacitances 
or indutances and its ratio of transformation is in relation to the 
ratio of primary to secondary capacitance or inductance.

> Tesla coils *do not* have iron cores, so it _must_ be an induction coil as
> I know some do.
     True Tesla coils do not have iron cores, BUT there are other 
things besides induction coils that have iron cores. There is a very 
simple device called a "kicker coil" that is nothing more than an 
iron core inductor! The priniple of the kicker coil is based on 
Michael Faraday's obseration that the faster a supply voltage is 
broken from an inductor the higher the counter E.M.F. generated. This 
by the way is why Dr. Tesla started out with mercury turbine 
interuptors and eventualy went on to using the disruptive disharge of 
a capacitor to drive the primary circuits of his High Frequency 

     Kevin's description of what his teacher demonstrated is rather 
ambigious and it is difficult to determine if he is describing an 
induction oil or a Tesla coil driven by a "kicker coil". The big 
difference is that an induction coil has both a primary and a 
secondary wound over the iron core while the "kicker coil" is just 
one large winding over an iron core. The origional reason "kicker 
coils" were used to drive some early amature Tesla coils was due to 
the lack of an A.C. supply. It is also a very good substitute today 
for the High voltage transformers we use , especialy for those who 
can't get neon sign transformers or pole pigs. For the benefit of 
those who may not be able to get H.V. transformers below is an ASCII 
diagram of a "kicker coil" driven Tesla coil. BTW some of you may 
recognize the ciruit is identical to that used in the hand held 
vacuum testers and the old "Violet-Ray" machines.
                                      ) S
                 VG ____  _|_         )
                      | | ___C        )P
                     #( |__|__________)
                   C #(    |
                   O #(    |
                   I #(    |
                   L #(    |
                      |    |
                     AC or DC

     The iron core coil is connected at one side of it's windings to 
the line. The other side of the coil connects to a vibrating armature 
identical to those found on the old induction coils. The stationary 
contact of the interrupter is connected to a 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 there is a capacitor C across the vibrating spark gap 
VG. There is an adjusting screw that pushes the moving armature of 
the vibrating spark gap closer to or further away from the stationary 
     For those who want detailed instructions for building this kind 
of Tesla coil look in Thomas Stanley Curtis's "High Frequency 
Apparatus" 1916 (reprinted by Lindsay Publications 1988)in chapter 
VIII "Kicking Coil Apparatus".


                              \\  ~ ~  //
                               (  -at- -at-  )
                           Alfred A. Skrocki
                             .ooo0   0ooo.
                        -----(   )---(   )-----
                              \ (     ) /
                               \_)   (_/