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

```Hi Bart, its Tab,
Firstly I'm a 17 year old A-Level college student, so if I make any
mistakes with CTop then tell me.
In all honesty I was not trying to solve the particular problem CTop going
down, but after you told me about it I came up with this...
Ok... a bit of background first
Once I had the resonant frequency of the primary circuit, the inductance
and the capacitance of the secondary coil I used the resonant frequency
formula
( substituting secondary coil inductance and setting it equal to the
resonant freq) to work backwards to find the capacitance I need from the
secondary circuit. I then subtracted the capacitance of the secondary coil
from this to find the capacitance needed from the torroid. I set the torroid
formula equal to this capacitance, substituted the D2 value of my aluminium
tubing in and used excels solver function to find the value of D1. This will
give me the final torroid dimensions.
This is what I want my program to do. 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.
set the formula, for total capacitance of capacitors in series, equal to
the total capacitance needed from the secondary circuit (this was gained by
setting res.freq and working back (look above)) and substitute the value of
the secondary coils capacitance into C1. Work backwards to find C2. This
will be the capacitance required from the Torroid. Now you can set the
torroid formula equal to this capacitance, sub in D2 and use excels solver
function to find D1. This will give the dimensions of the torroid.
When you place the torroid on the secondary the total capacitance will
go down to the required level!!!
OK guys check through this and let me know of any mistakes, if it's ok I
will incorporate it into my program.

Thanks for the help

Tabraze Malik

>
> Hi Tab,
>
> Just curious: I understand your developing a Tesla program, but what are
you
> trying to actually do with Ctop? I'm curious because top capacitance is
simple
> to calc in a program (as a stand-alone toroid) with 2 inputs:
> Ctop(pF) = ((1+(.2781-d2/d1))x2.8)*(sqrt(2pi^2(d1-d2)*(d2/2)/4pi)) for a
> toroid.
> d1 = diameter of toroid
> d2 = diameter of cross section
>
> The problem with Ctop is that once it is placed on the secondary, it
appears to
> partially lose some of it's capacitance. I'm curious if you are looking
into
> calcing Ctop based on the coil parameters and if so, what those parameters
are.
>
>
> Thanks,
> Bart
>

```