# [TCML] Primary selfC

Chris Swinson list at future-technologies.co.uk
Fri Jul 25 05:06:27 MDT 2008

```Hi Bart,

6.4nF sounds  more than I thought :S  in fact if this is the case I could
just re-work my primary to give 3nF in SelfC and not even have to bother
having the tank/tuning  cap..

calculator ?

I am not sure about the effects of the secodnary on my primary... K is about
0.05K so hopefully it will have have too much effect... though I need to get
some ballpark figure with the primary itself before I can start to worry

I will assume that the primary SelfC will increase when the secodnary is
inserted ? If it works out a ballpark of 1nF for example, then I will
re-work my primary to say 2nF....

Chris

----- Original Message -----
From: "bartb" <bartb at classictesla.com>
To: "Tesla Coil Mailing List" <tesla at pupman.com>
Sent: Friday, July 25, 2008 2:45 AM
Subject: Re: [TCML] Primary selfC

> Hi Paul, Chris,
>
> It might be more accurate to look at the total length of the ribbon and
> width to determine area and treat it as rolled capacitor separated by 1mm,
> using air as the dielectric, and determine C as one would with any flat
> plate capacitor, but in this case, as a "rolled capacitor".
>
> C = 0.2248*k*A*(N-1)/(d*x)  (in pF)
>    where
>     k = Dielectric constant (1.0006 for air)
>     A = Effective plate area in square inches (length x width)
>     N = Number of conductive plates (3 for a rolled cap)
>     d = individual dielectric film thickness (.03937" in this case)
>     x = number of stacked sheets of dielectric between plates (1 in this
> case)
>
> I think Chris is looking at about 6.4nF for the ribbon primary. So he's
> probably correct to ask the question given the very low tank capacitance.
> Primary C may be much higher than expected (a good deal of area at about
> 557 square inches). Should be able to verify by inserting a signal to the
> primary as one would with a secondary and looking in the range of 470kHz
> assuming inductance is about 18uH.
>
> Regards,
> Bart

```