# Re: Tesla Software

```Hello Tesla Software Fans,
Graham Armitage <armitage-at-tiac-dot-net> wrote:
<snip>
>Firstly, what is considered the best formula for calculating primary coil
>properties. I presume most people are winding flat (or inclined) copper
>tubing primaries. I know nothing here will be deadly accurate but must at
>least to get into the right ball park.
The basic formula for a flat spiral can be found in the funet
archives in the file math.txt.  A flat spiral can be constructed out of flat
ribbon (a la aluminum or copper flashing) or using soft copper tubing.  The
latter is perhaps a little more popular.  Although a correction for the
tubing thickness can be employed, the crude formula gets you close enough
experimentally.
People also construct primaries as solenoidal coils, and/or as
inverted conical (inclined, also called "saucer") coils.
Wheeler's formula works fine for a solenoidal primary coil.
For an inclined flat spiral, I estimate the inductance in the
following manner:  Assume one has a coil with inner diameter D1 and outer
diameter D2, with the outermost turn elevated H inches above the innermost
turn, with N turns.  Compute inductance L1 using Wheeler's formula for a
solenoid with diameter D=(D1+D2)/2, N turns and height H.  Next, compute
inductance L2 for a flat spiral using the funet formula using the parameters
D1, D2, and N.  Next, compute angle=arctangent(H/T) (in radians) where
T=D2/2-D1/2 (coil thickness).  Define F1=angle/1.5708, and F2=1.0-F1.
Finally, compute the inclined flat spiral coil inductance L using the
weighted average: L = L1 x F1 + L2 x F2.  This is simply a weighted average
of a flat spiral coil and a solenoidal coil, with the weighting changing
linearly as the coil height changes.  This formula will usually get you to
within 10% or so.

>
>Secondly, does the formula for calulating capacitance of plat plate caps
>work for rolled caps? I seem to remember there being a slight difference.
>Does anyone really worry about calculating the capacitance from physical
>dimensions before construction or does available material size determine the
>size cap to build?
The flat plate formula is in the funet file math.txt, or look in a
copy of the Radio Amateur's Handbook.
Ideally, I would like to specify the capacitance, and then play
around with the capacitor size and number of plates to make it work.  I
would ALSO like to be able to just play around with the capacitor geometry
and see what capacitance value I get, for most flexibility.  There should
also be some general guidance in the program regarding a safe operating
voltage based on the dielectric thickness and type of materials used.
For a rolled capacitor you get twice the capacitance.  I think the
formula is the same except for the factor of two.  I'll have to check my
notes at home.
Regards,
Mark S. Rzeszotarski, Ph.D.
```