Re: Dual Layer Primaries

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Pete Komen by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pkomen-at-zianet-dot-com>

I looked at this a while back and came up with calculations for this.  I
wasn't going to reveal them until I was able to test, but since the results
are not too far off John Freau's measured values here it is.  This is
limited to two spirals with the same number of turns.  It doesn't visualize
well when the separation of the spirals is not an integral number of tubing
diameters, but the numbers look ok.

Given:

Diameter of Tubing: Dt                                 0.25
Separation of turns: St                                 0.25
Number of turns per spiral: N                        13
Radius of inner turn: R                                  4.25
Separation of spirals: Ss                               1

Calculate:
Width of spiral: d                                           6.25
Radius to center of spiral: r                            7.375

Imagine the separation filled with turns: (New Nt = 78, length = separation
+ thickness of spirals = 1.5)
Calculate the gross inductance:
Lg = (0.8 * r^2 * Nt^2) / (6 * r + 9 * length + 10 * d)           = 2201.5
(in microhenries)

Calculate the inductance of one spiral plus the middle: (Nsm, length =
separation + thickness of one spiral)
Le = (0.8 * r^2 * Nsm^2) / (6*r + 9 * length + 10 * d)          = 1558.0

Calculate the inductance of just the imaginary middle: N and length vary
again.
Lc
= 1016.5

Mutual inductance:
Lm = (Lg + Lc - 2 * Le) / 2                                              =
51.0

Calculate the inductance of one spiral:
Ls = ( r^2 * N^2 ) / ( 8 * r + 11 * d)                                    =
72.0

The total inductance:
L = 2 * Ls + 2 * Lm
= 245.9

I have all this in an Excel spreadsheet so the numbers are easy to
manipulate.

Here's John Freau's measurements (on his diagonal where the top and bottom
spirals have the same number of turns) and my calculated number:

N               John                    Mine
13              250                     243
12              204                     204
11              170                     169
10              134                     139
  9              110                     110

I am hoping that those who can check this will feel motivated to do some.
This is only a theory, please feel free to prove it wrong.

I was working from a few pages copied from a textbook (I think I can find
them again) that developed calculations for the inductance of two helical
coils spaced apart on the same form.

Terry,

I have attached an Excel file with the calculations for this.

http://hot-streamer-dot-com/temp/TeslaTwoSpirals.xls

Regards,

Pete Komen