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.

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.