# Re: Torroid Formula (To Bart + All others)

```Tesla List wrote:
>
> Original Poster: "Tabraze Malik" <tab-at-malik13.freeserve.co.uk>

> Now coming to the problem...
>     If you have the secondary coil (which obviously has capacitance) and
> connect the Torroid to it then basically what you have is 2 capacitors
> connected in series. The formula for capacitors in series is
> (1/CT)= (1/C1) + (1/C2).....
> where CT = total capacitance and C1 , C2 are the capacitances of the
> capacitors in series  (for as many caps you have in series). If you look at
> this formula it's not a big leap of maths to see that the total capacitance
> will be less than the capacitance value of any capacitor in series. This
> might explain why capacitance goes down when placed on the secondary.

No... The terminal capacitance is in parallel with the self-capacitance.
Both are distributed capacitances from the top of the coil to the
vicinities. Ct=Ctop+Cself. There are small variations in Ctop and Cself
due to the interconnection, but this can be ignored as a first
approximation.