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RE: TC Primary Coil (was My first TC)

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
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

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

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>"

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?

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John Couture

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