# Re: Rotary Spark Gap Design

```Hi all,
Rod, I was interested to see the specs. you posted on the
large coil. I would be interested to know the height of the secondary
winding as near as poss. to calculate the theoretical maximum output
which I suspect isn't even close 3.5MV. Reason? There is a reality
check you can do :
Assume that Cp is charged up to it's highest possible voltage
and that ALL this energy gets transferred to the total secondary
capacitance (Cself+Cterminal) (ignore gap losses), the theoretical
Vs(pk) = Vp(pk) x SQRT(Cp/Cs). This is easily derived from a
conservation of energy viewpoint. Also, since Cp.Lp = Cs.Ls  (tuning
requirement), Vs(pk) = Vp(pk) x SQRT(Ls/Lp). This second equation is
given in two separate papers that I know of (one was Hoffman).
On this basis I shall stick my neck out : Robert Golka isn't
getting anything like 12+ million volts (I suspect he is doing a spark
length estimation which is totally inaccurate for high frequency
discharges). I would expect absolutely humungous sparks for 3.5MV
at T.C. frequencies.
I'll be interested to hear what others have to say.

Malcolm
....................................
You wrote :
> The original design was taken from Bill Wysock's
> 3.5MV Super Model 9 Tesla Coil.
> We have this coil in our National Science and Technology Centre
> (Questacon), Canberra Australia.
>
> Very impressive too!
>
> Specs:
> ------
> Power Supply - 20KV -at- 12.5KVA
>            Current and Voltage Limited by variacs of some kind.
>
> 2 x 0.1uF Caps in series = 0.2uF -at- 50KVDC each.
>
> Rotating Spark Gap (see GIF file)
>
> Primary - 5 turns 1/2" copper pipe, archimedes flat spiral
>       Outside Diameter - roughly 28" - 29"
>           Inside Diameter - 2" larger than secondary, ie, 1" spacing
>                 between primary and secondary.
>
> Secondary - 800 Turns of 3mm (appears plastic insulated)
>         Diameter - roughly 15"- 18"
>
> 30" x 10" professionally made Alluminium toroid
>
> Frequency - 80Khz
>
> Output - 3.5MV (at full power)
>
> Spark Lengths - roughly on average 6-10 feet.

<snip>
```