Re: Tesla Coil Electrical Fields - was Dangers of running 2 coils...

John and all,

My comments are interspersed below...

-- Bert --

Tesla List wrote:
> Original Poster: "John H. Couture" <COUTUREJH-at-worldnet.att-dot-net>
>   Bert -
>   How do you think the resonator was excited? Was the energy transfer by
> electromagnetic fields or by Faraday fields a la Terman or was it something
> else?

John, since a common base ground was used for both coils, I'd suspect
that the predominant energy transfer mechanism was _direct_ coupling.
The operating coil generates significant RF voltage and spikes on the
common resonator groundline. For example, even though I use 3 eight foot
groundrods, I've measured spikes of 600 hundred volts, and resonant
frequency voltages of over 160 volts on the resonator groundline of my
10" coil. If the passive resonator is not breaking out, the Q of this
resonator may be as much as 200-300. For similarly-tuned resonators this
alone can generate significant output on the passive resonator - this
effect can be seen by retuning an temporarily operating a balanced twin
coil system off only ONE active primary, or by operating a balanced twin
with NO ground to the common base connection.

The passive resonator was also most likely lightly coupled to the active
system though near-field EM coupling from the active primary since the
two systems were fairly close together. I have little doubt that this
form of coupling also a contributing factor, especially if the two
systems were of similar operating frequencies. 

A couple of other interesting questions could be asked about Brian's
- how did energy transfer from the secondary to the primary circuit of
the passive system  [I'd bet by EM coupling between primary and
- how did preferential rectification occur to charge the primary
capacitors in the passive coil?  [Beats the heck outta' me!]

>   Are you willing to take a stab at describing "displacement currents". Do
> they even exist? I believe there are only three types of electrical
> currents, active. reactive, and the vector sum of these two, the typical
> WATTS, RVA, VA triangle.
>   John Couture

I'll try to give this a brief shot...

Maxwell was initially thinking of the behavior of dielectric MATTER at
the molecular or atomic level, or of the ether of his day in a vacuum.
He theorized that an externally applied electric field "displaced" the
positive and negative portions of the particles within the dielectric
material - and the resulting external current was the "polarization
current" of the dielectric. Since this effect is also observed in a
vacuum, this implies an elastic-like behavior of space itself (or the
ether) - Maxwell likenned it to an "elastic membrane" holding back a
fluid in one of his many mechanical analogies. 

In a very strict engineering sense, you are correct. Displacement
current _within the dielectric_ is certainly not an ordinary conduction
current since, discounting leakage, no actual flow of electrons is
taking place through the dielectric. And, the current flowing through
the external conductive circuit only flows when we apply a time-varying
voltage to the capacitor plates. Since this is a transfer of energy to
or from a lossless energy-storage element, the current flowing through
the metallic circuit is a pure reactive current as you've suggested.  

Ultimately, I suspect that the disagreement surrounding conductive and
displacement currents is mostly one of semantics. There's little doubt
in my mind that the free-air streamers of a Tesla Coil are indeed
conducting displacement currents, as the isotropic capacitance is
charged and discharged through the conductive plasma of the discharge.
These currents can be quite large when the streamers actually initiate
or propagate. Richard Wall is also correct in contending that the
visible streamers are acting as [lossy] conductors, and that the heavily
conductive portion of the discharge is not behaving as a good

However, as we go outward along a streamer path, the surrounding air
grades from being a conductor within the main channel, to a more poorly
conductive/leaky dielectric as we reach the streamer tips, to a very
good dielectric far away from the streamer tips. While we can quibble
about ion clouds, space charges, and just "where" the other plate of
this isotropic capacitor appears to be, the non-conducting dielectric
space beyond the air streamers still "insulates" the two plates of our
isotropic capacitor from true conductive current flow. The visible
streamers appear as lossy extensions of our metallic circuit, having the
effect of inserting a dissipative element in series with an otherwise
relatively low-loss oscillating secondary LC circuit...

Safe speculatin' to you! 

-- Bert --


>> I looked at the pictures and the coils were about 14' apart.  I was running
>> about 2kva at that time if I remember correctly (we made many changes that
>> evening) and was having some trouble getting breakout with the topload
>> configuration at the time. Don't know if it makes any difference but we
>> both sharing a common ground wire (Ground rod with a 10' lead to my coil
>> then 10' more to Ross's coil).
>> Regards,
>> Brian D. Basura