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Re: Elementary Inductance.
Tesla List wrote:
>
> Original Poster: "JimmyD" <jim_del-at-email.msn-dot-com>
>
> I know this is an elementary question, and that it may have been answered
> before on the list but,
>
> In _lay terms_ , what determines the inductance in a coil?
>
> The diameter, the height, the guage of the wire, the number of turns or the
> length of the wire?
It is a good question. The inductance is primarily determined by the
number of turns, the area covered by the turn, and how close they are to
each other. The closer together, the more "mutual coupling" there is,
which increases the inductance. The physically smaller the coil, the
closer each piece of wire is to all the other, which increases the
coupling, which increases the inductance. A long straight piece of wire
has very low inductance (about 1 uH/meter), because each part isn't very
close to any other part.
A multilayer solenoid has high inductance, because all the turns are
close together.
A pancake coil (a flat spiral) and a regular single layer solenoid are
somewhere in the middle because the flux from each piece of wire couples
somewhat to each other piece.
The gauge of the wire doesn't have much effect, except as it limits how
close the windings are to each other.
>
> In tesla operation what is the relationship of the primary to the secodary?
> The guage? The number of turns? The diameters? The heights?
A TC can be considered as two coupled tuned circuits. The best way to
look at is NOT as a transformer (where the turns ratio is important).
Think of the stored energy in a tuned LC circuit. The energy moves back
and forth between the Capacitor and Inductor (E= CV^2/2, or E = LI^2/2),
so when the voltage on the cap is at a peak, the current in the inductor
is at a minimum.
Consider the whole thing as an energy transfer problem. The energy in
the secondary top load will (by definition) be less than the energy you
originally put into the primary capacitor. Use the capacitor energy
equation to figure out the max voltage the secondary can reach: Vsec^2 *
Csec = Vpri^2 * Cpri or.. Vsec = Vpri * Sqrt(Cpri/Csec). You can see
you want big Cpri and little Csec. This implies little Lpri and big Lsec
(because the resonant frequencies have to be the same: Lsec*Csec =
Lpri*Cpri). The tricky part is getting the high Lsec with a low
loss.....
The transformer puts energy into the primary cap. The spark gap fires
forming an LC circuit in the primary, some of the energy that is in the
primary L couples to the secondary L. The energy then moves from the
secondary L into the secondary C (making its voltage real high). Then,
of course, the energy moves back from the secondary C to the secondary
L, then back into the primary L and back into the primary C. At each
stage, some power gets lost, so the waveform looks like a damped
sinusoid.
The trick is in getting enough power to go to the secondary C, and then
suck it off in a big spark, before it couples back into the primary.