Re Am I Right ? (fwd)

---------- Forwarded message ----------
Date: Wed, 15 Jul 98 10:02:24 EDT
From: Gary Lau  15-Jul-1998 0932 <lau-at-hdecad.ENET.dec-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re Am I Right ?

>From: quantum3 <quantum3-at-geocities-dot-com>
>I think I understand now what is going on inside the Tesla coil, but
>correct me if I am wrong.
>We need to achieve maximum current transfer through the primary coil
>(Tesla coil). To achieve this we  need to achieve resonance between the
>primary and secondary coils. Maximum current transfer occurs only at
>resonance where the impedance is at the lowest level. With nearly zero
>resistance  to current flow, maximum field can be achieved and induced
>directly into the secondary winding.

If you just are looking at the primary, it doesn't matter to what frequency it
is tuned, it will be resonant at some frequency and it will ring following gap
ignition pretty much the same as far as current flow, just at different

POWER transfer is a different matter.  Now it matters that the secondary
matches the primary's resonance.

>The secondary winding having many more turns then the primary, converts
>all available current to voltage (ohms law). 

Ohm's law doesn't apply here.  A Tesla coil would work quite nicely if
there was no resistance, and having some only has a small effect.  What
is happening is that the energy in a L-C circuit ringing at resonance
alternately exists as current in the inductor, then as voltage across the

>So resonance regardless of
>coil dimensions must be achieved regardless of all other factors, though
>they are important. The spark cap and the capacitor provide resonance
>for the primary windings. 

The spark gap does not affect the resonance frequency, it just determines
at which point in time the primary cap's energy is dumped into the tank,
and it also completes the tank circuit while the tank rings down.  (Much
additional information about quenching omitted here, see other recent posts)

>If I look at this from a different angle
>however (for example; audio circuits), most of the circuits contain a
>capacitor also on the secondary winding to adjust the resonance on that
>side of the circuit too. However in many designs of Tesla coils I do not
>see this (cap on the secondary). Why is this ?  

I'm not sure which audio circuits you're refering to with a cap in the
secondary circuit.  The reason that you don't see a secondary cap in
many Tesla coil schematics is that they are not two-leaded components as
in the primary circuit.  There are two things that make up the secondary
capacitance:  The self-capacitance inherent in the adjacent secondary
windings, and the capacitance to ground exhibited by the toroid.  The
capacitance is there, you just don't see what looks like a capacitor.

>Thanks, & Good Luck !  Fred.

Regards, Gary Lau
Waltham, MA USA