# Re: Grounds

``` -=> Quoting Nikola Tesla (chip Atkin to Tesla List <=-

NT(A> T(A> Message-ID: <9412191544.AA11940-at-grendel.objinc-dot-com>
NT(A> Newsgroups: tesla.list

NT(A> Hi Everyone,

NT(A> Here's a question that I have been wandering for sometime but I cant
NT(A> seem to find any books to answer it. The question is why is a good
NT(A> ground so essential for Tesla coil work? Why wont a Tesla coil produce
NT(A> nearly as good a spark if it doesnt have a good ground?

NT(A> I know that the earth acts as a good conductor that can carry away
NT(A> excess charge from an object but I cant see how this would help in
NT(A> Tesla coil work. I guess its the same question as why a radio
NT(A> transmitter needs a good earth to transmit efficiently (a ground
NT(A> plane?)
NT(A> I have looked for answers in the ARRL handbook and lots of others but
NT(A> I cannot find anywhere a reference that explains about grounding.

NT(A> Anyone out there know?

NT(A> Cheers,
NT(A> Mark

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

MG> Mark, grounds in a Tesla coil system are necessary because the base
current in the secondary circuit return via the ground path near the base
of the coil. It is difficult to explain without aid of a drawing, but I will
give it a try.
The secondary system can be explained in several different manners but the
simplest way is to view the secondary coil as a series resonate circuit
comprised of its self-inductance and capacitance. If you can, refer to my
article in the TCBA news Vol.12 #4  pgs. 14-16. The secondary coil can be
viewed as a inductor placed vertically over a ground plane (earth) the
terminal capacitance would be at the top end of the coil, now, imagine the
coil as being hundreds of series connected inductors I.E. if the coil has
500 turns, call it 500 series connected inductors, but for the sake of
discussion, lets draw 5 series inductors, and from each connecting point
between the inductors draw a capacitor to the ground plane, the highest
capacitor being from the terminal capacitance to the ground plane. Now,
you should have a drawing of a segmented coil with 5 capacitors to ground
and the bottom of the coil should also be connected to ground. It should
be obvious on examination that the inductive reactance will rise as the coil
moves farther and farther from the ground end because the inductance is
increasing, the same is true with the capacitive reactance because the
capacitance to ground is DEcreasing, thus the total impedance of the
of the coil rises as you approch the top of the coil. The impedance at the
top is the highest thus that is where the voltage is the highest, the
impedance at the base is the lowest, that is where the current is the
highest. The ground is the common connection in the circuit that connects
the bottom of the inductor to the capacitance, If there is a poor
ground system it has the effect of placing a resistance in series between
the bottom of the inductor and the capacitors, thus limiting the Q of the
secondary system it would in effect be a resistive loss limiting the
current flow in the secondary circuit. Thats why improving the ground, or
increasing the size of the terminal capacitance will improve coil operation,
it increases the current flow in the secondary coil as long as
there is enough power being fed to it to take advantage of it. Increasing
the terminal size lowers the impedance at the top of the coil increasing
the current flow in the entire secondary coil.

It is interesting to note that the base current in the secondary coil will
continue to rise with increasing power input in a nearly linear manner
until a discharge occurs at the terminal, then the power input increase
becomes logarithmic in nature with reference to the base current, that is
why for energy transmission no discharge from the terminal is desired, it
limits the ground current.

I hope that makes some sense to you, read up on voltage division in series
resonate circuits, that may help.

Mark Graalman   TCBA # 1399
5004 South Ave.
Toledo, Ohio 43615-6429

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

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