rolled caps

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: rolled caps
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 19 Apr 1998 17:25:32 -0500
Approved: tesla-at-stic-dot-net

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From:  Kevin Wahila [SMTP:kevinw-at-stny.lrun-dot-com]
Sent:  Sunday, April 19, 1998 11:43 AM
To:  tesla-at-pupman-dot-com
Subject:  rolled caps

a while ago i began planning and construction of my first rolled caps.
since then my coiling was put on hold for some time.  now, as i go back and
look through my mail and information to refresh my memory, i have found a
slight problem dealing with the equation to calculate capacitance for a
rolled cap.  i have two different mails from the list with two different
answers

#1......

            0.224 x K x A
       C  = ------------- x (N - 1)
                  D

C = Capacitance (in microfarads)
K = Dielectric constant
D = Distance between plates in inches
A = Area of plate in inches
N = Number of plates

and....

#2.....

                          2.248965 * 10^-7 * K * A
C (microfarads) = ------------------------------------ * (N-1)
K=dielectric 
const.
                                         d

!!!Again, you need to multiply this result by 2 for a rolled up cap.
This is the formula I generally use when making homemade caps.

ok, so which one is the right one?

thanks,
Kevin