# Re: Re: Grounds

• To: tesla-at-grendel.objinc-dot-com
• Subject: Re: Re: Grounds
• From: mark.graalman-at-mediccom.norden1-dot-com (Mark Graalman)
• Date: Thu, 12 Jan 1995 17:49:00 -0500
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NTAC> Anyway, here's  a few more questions for ya if you have a spare
NTAC> moment!
NTAC> MG: increasing, the same is true with the capacitive reactance because
NTAC> the capacitance to ground is DEcreasing, thus the total impedance of
NTAC> the  of the coil rises as you approch the top of the coil. The
NTAC> impedance at the top is the highest thus that is where the voltage is
NTAC> the highest, the  impedance at the base is the lowest, that is where
NTAC> the current is the  highest. The ground is the common connection in
NTAC> the circuit that connects

NTAC> Ok impedance=voltage/current , so high impedance means high voltage.
NTAC> But hold on: in a series LCR circuit isnt the high voltage due to a
NTAC> high current flowing thru a high reactance? So if we regard the Tesla
NTAC> coil as a series LCR circuit shouldn't the current be large throughout
NTAC> the coil - including the top end of the coil? (Is the current that
NTAC> flows in a series LCR circuit the same anywhere in the circuit?)

MG> First, let me point out that E/I=R, the word impedance implies the
presence of reactance and a reactance can't dissipate power, so to be
truthful in our calculation of impedance phase angles must be taken into
account. With that aside, I understand your question, and I will try to
explain.
The current in the coil decreases with increasing distance from ground
because the capacitance to ground decreases. Again, lets look at our 5
capacitors to ground and assign them values. Starting at the 1st up from
the bottom, lets call this 20 pf., the next up 10 pf., the next 5 pf., the
next 2 pf. Now you have 4 paths for current flow from the secondary coil,
the lowest reactance is, thus the highest current will flow through the
20 pf, and gradually decrease going up and through the next lower values.
Now, if we install a 30 pf terminal on top of this coil, the effect of this
terminal will be to "absorb" the various capacitances inert in the coil
itself. Thus the coil capacitance becomes 67 pf with most of it lumped at
the top of the coil, rather than distributed acrossed the coil. It raises
the current level in the upper part of the coil, this is what "old timers"
refer to as "drawing the energy out of the coil".

I know your thinking this is not a series circuit, but understand that's
determined by how energy is applied to the circuit, not the wiring of it.
We have to view it from the "inside" sor - to - speak. Maybe it would be
easier to understand if I told you that using a ribbon conductor at RF
results in a situation called "current bunching" on the edges of the ribbon.
Or skin effect causing the current to flow near and on the surface, there
is only one path, one conductor, but different paths WITHIN IT.

NTAC> MG:Thats why improving the ground, or
NTAC> increasing the size of the terminal capacitance will improve coil
NTAC> operation,
NTAC> it increases the current flow in the secondary coil as long as
NTAC> there is enough power being fed to it to take advantage of it.
NTAC> Increasing the terminal size lowers the impedance at the top of the
NTAC> coil increasing the current flow in the entire secondary coil.

NTAC> Lets see if I get this: increasing the terminal size increases the
NTAC> capacitance of the top of the coil. So the capacitance between the top
NTAC> of the coil and the ground is bigger. This means that capacitive
NTAC> reactance is smaller so more current flows in the circuit. But at
NTAC> resonance isnt the current that flows in a series LCR circuit only
NTAC> limited by the resistance as capacitive reactance and Inductive
NTAC> reactance kill each other?

MG> The frequency drops, so does the RF resistance and remember the
reactance voltage drops are treated individually, they are +90 and -90
degrees, so if taken together they equal zero and leave only resistance.
Thats how the drop across one reactance can exceed the applied voltage and
its called "resonate rise". I'm aware that the secondary is discribed many
ways, as a "helical resonator" a "1/4 wave transmission line" etc. But
nobody states that these examples are talking about the same thing, just
different names, and applications. In all cases, the potentials are
developed acrossed a reactance and all are 90 degrees in ELECTRICAL length.
What is grossly incorrect is the 1/4 wavelength of wire discription.

NTAC> Another thing that I dont understand is this wireless transmission of
NTAC> power thru ground currents. If we have ground currents flowing wont
NTAC> this ground current try to capacitively couple to the top of the coil
NTAC> and so "complete the circuit" instead of flowing miles away to light a
NTAC> distant lightbulb on top of another coil?

MG> I don't feel real free to comment on this, because I've never really
persued a good understanding of Tesla's thoughts on this, and I don't want
to create greater confusion. But I will say if what you stated in the above
were true, no radio station would ever send out a signal!
I don't believe that power transmission through ground currents could be
accomplished in a true and usable sense with the frequencies of a typical
tesla coil (50-700 khz.) I think you'd have to go down around 5 Hz. for a
standing wave to occur in the earth, but again, its just my un-educated
thoughts on the matter. I would think the limits on this with a "typical"
coil would be around 3-5000 feet. Not to mention that there is a BIG
difference between drawing a few milliamps for a bulb, and enough power to
run a house full of stuff, we basically live in a "low impedance world".

NTAC> Sorry about all these questions but I am really bamboozled trying to
NTAC> understand how a Tesla coil works. Just when I think I have a handle
NTAC> on it some new facts come along that blow my ideas to hell.

MG> Ah, bolderdash! Just make BIG sparks, its fun.

NTAC> Best Regards,
NTAC> Mark

NTAC> -- Mark
NTAC> _/_/_/   _/_/_/_/       Mark Conway
NTAC> _/    _/    _/          Deep Thought BBS, Auckland, New Zealand
NTAC> _/    _/    _/          A FirstClass(tm) Macintosh GUI BBS
NTAC> _/_/_/      _/          Internet: mconway-at-deepthnk.kiwi.gen.nz

... Alias, Mark the Spark
___ Blue Wave/QWK v2.12

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