# RE: TC Primary Coil (was My first TC)

```Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Thanks for the elaboration John. I think the original poster
questioned why there is more inductance per unit area in the outer
portion of a spiral rather than at the centre. He didn't refer to
helices at all. My reply was an explanation to him. Pri-sec
clearances didn't figure in the original question either unless my
memory fails me.
A quick (rough) calculation shows that the length of copper in
both examples below is roughly the same at around 38 feet. Both have
the same inductance. Does N (number of turns) matter in single layer

Regards,
malcolm

On 1 May 01, at 8:03, Tesla list wrote:

> Original poster: "John H. Couture by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>
>
>
> Malcolm -
>
> I was referring to comparing a Tesla coil when only the shape is
> changing from a spiral primary to a helical coil primary, all other
> parameters remain the same. For example using the default coil of the
> JHCTES Ver 3.2 program the parameters would be:
>
>   Spiral Coil
>   Avg Rad = 7.0   Inner turn = 4.5   Pri/Sec Clear = 1.5
>   Width of Turns  = 5.0   c/c spacing = 0.50
>   Pri turns = 9.98   Lp = 43.93 uh    Res Freq = 169.80
>
>   Helical Coil
>   Avg Rad = 4.5    All turns = 4.5    Pri/Sec Clear = 1.5
>   Height turns = 8.1    c/c spacing = 0.50
>   Pri turns = 16.24   Lp =43.94 uh     Res Freq = 169.80
>
> Note that the Avg Rad (input) is adjusted to give the same Pri/Sec
> Clearance (1.5)(output). The Width of Turns and Height of Turns
> (inputs) are adjusted to give the same c/c spacing (0.50)(output).
>
> I have never heard anyone mention this unique spiral primary to
> helical coil primary relationship. When the turns are closer you
> normally need less turns not more. You can verify this with the coil
> configuration. Reduce only the coil height from 8.1 to 5.0 and the
> primary reduces from 16.24 to 14.01 turns.
>
> The JHCTES program uses the Wheeler equations for the spiral primary
> and the helical coil primary. An interesting problem with the program
> is to find the capacitance of the primary capacitor for only one
> primary turn. Both the spiral and the helical coil calcs will show the
> same capacitance with no other changes. This is an iterative problem
> for the math minded who would insist on going  thru the many
> calculations required. Developing these two empirical equations must
> have been a very difficult job for Wheeler.
>
> Playing with a TC program can teach you almost as much about Tesla
> Coils as building and testing them but is not as much fun. However,
> with the program you can check a lot of TC combinations easily and
> quickly compared to building and testing them.
>
> The web site for the on line JHCTES Ver 3.2 program is at
>          http://home.att-dot-net/~couturejh/
>
> Don't forget to click "Calculate" after all changes.
>
> John Couture
>
> --------------------------
>
>
> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Sunday, April 29, 2001 2:59 PM
> To: tesla-at-pupman-dot-com
> Subject: RE: My first TC
>
>
> Original poster: "Malcolm Watts by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>
>
> On 28 Apr 01, at 19:08, Tesla list wrote:
>
> > Original poster: "John H. Couture by way of Terry Fritz
> > <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>
> >
> >
> > I agree with only some of the explanations below and would like to
> > point out an interesting result of comparing the primary spiral coil
> > with the helical coil. The flat spiral primary winding always has
> > less turns than the helical coil winding (same c/c spacing) for the
> > same amount of inductance using the Wheeler equations.
>
> They are two different geometries governed by two different
> equations. There has to be some parameter definition in order to make
> a useful comparison. For example, how do the heights differ? Is the
> length of copper in each the same? Is the mean radius of each coil the
> same? A worked example would be very useful.
>
> > Who can explain why you need more turns for the helical primary when
> > the turns are closer to the secondary coil compared to the spiral
> > primary when turns are farther away? Contrary to coupling theory?
>
> In order to do what? Achieve the same coupling constant?
>
> ----------------------   snip
>
> John Couture
>
> -----------------------   snip
>
>
> Regards,
> Malcolm
>
> -------------------------  snip
>
>
>
>

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