# *efficient tesla coil

```Hello all,

>enough input power is used, the BEST amount of terminal capacitance is
>the amount that would cause ACTUAL 1/4 wave resonance in the secondary
>winding, I.E. a coil wound with 1800 feet of wire may resonant at around
>230 to 250 Khz.with no terminal on top, but the WIRE in the secondary
>is a physical 1/4 wave at about 130 Khz. If a terminal is added to this
>coil that would result is ACTUAL 1/4 wave resonance in the secondary or
>in this case about 130 Khz, I believe at this point, ALL internal
>capacitance of the secondary windings has been absorbed by the terminal
>and then the secondary system can be treated in a lumped constant format.

This addresses a prblem that I have not been able to reconcile with the
calculations until now. No matter what I calculated the secondary resonance
to be at 1/4 wave, I always had to "halve" my primary inductance to get
resonance in the secondary! Now I see that the calculations were correct,
but that there is some property of the secondary wire-length vs. resonant
frequency that I am not aware of. It seems like a 1/4 wave-length of wire
resonates at the half-wave frequency or something like that. This is
without a terminal capacitance, of course. Can anyone shed some light on
this? And Mark, thanks for this valuable info!

And Richard:

>Figure between 160 - 170 microFarads if you are using both
>transformers with primaries wired in parallel on a 120 volt
>buss.

>cutting the rubber insulation for taps, you will only need about
>4 taps per turn.

>will go even higher. I would expect that this system will produce
>a 60" spark (five feet) with regularity. You are up to the point
>where a "code" ground is not going to provide optimum perform-
>ance, not to mention safety. I would feel better if you were
>talking about three, perhaps even four times, the surface area
>contact with moist earth. Three six foot lengths driven in a row
>six feet apart, with depresssions around the pipes to collect
>moisture. I would connect the pipes with 1" tinned copper braid
>ground strap buried six inches deep. I would also water the
>ground down a bit to increase the conductivity before I fired.

Thanks for this valuable info, too! I will do as you suggest.
If someone had told me that it was possible to get a five-foot spark
out of a two-foot coil, a year ago, I would have thought they were very
uninformed. Now I have a whole new perspective on what's going on with
these things. This project should be complete in about 2 or 3 weeks.

Will keep y'all posted!

Dan

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