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"Slinky" Primary / Sloped Archimedes Spiral Primary Equation


----------
From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Monday, August 17, 1998 2:41 PM
To:  Tesla List
Subject:  Re: "Slinky" Primary / Sloped Archimedes Spiral Primary  Equation


  Bert -

  These questions came to mind as I was using the equations you show for
the TC inverse cone type primary.

  1. What are the advantages/disadvantages of the cone type primary?
  2. How would you determine the optimum angle?
  3. What are the advantages/disadvantages of using a cone type primary
with a raised secondary?
  4. How would you determine the best cone angle and best approximate
location for the secondary for later tweaking?

  I found that for the typical TC spiral primary as the angle is increased
from zero degrees (flat spiral) to about 30 degrees the inductance
increases slightly. As the angle is increased more the inductance begins to
decrease until it is about one third the zero degree value at 90 degrees or
the coil value. The inductance increases then decreases only slightly up to
about 45 degrees so the flat inductance value could be used for all cone
type primaries under 45 degrees because the differences are within the
error tolerance. 

  With a fixed secondary and inductance (Ls) the secondary voltage varies
as the   sqrt(Ls/Lp).    This would indicate a coil type primary (Lp) would
give more secondary voltage and spark length than the spiral primary
because the inductance is less. We know this is not correct so what are the
optimum spiral primary design criteria?  

  John Couture

--------------------------------------  


At 11:38 PM 8/14/98 -0500, you wrote:
>
>----------
>From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
>Sent:  Friday, August 14, 1998 12:06 AM
>To:  Tesla List
>Subject:  Re: "Slinky" Primary / Sloped Archimedes Spiral Primary Equation
>
>Tesla List wrote:
>> 
>> ----------
>> From:  Dave Sharpe [SMTP:sccr4us-at-erols-dot-com]
>> Sent:  Wednesday, August 12, 1998 9:51 PM
>> To:  Chip Atkinson
>> Subject:  "Slinky" Primary / Sloped Archimedes Spiral Primary Equation
>> 
>> Chip, ALL
>> 
>> A while back, (before the detonation of my HD :^C ) I has saved a copy
>> of a post for a sloped "pancake" primary inductance and tubing length
>> based on coil ID, OD, spacing and included acute angle from horizontal
>> plane.  I've tried searching in archives without success.  If someone
>> could privide I would appreciate it greatly.  I'm contemplating building
>> a small (450VA/ 15kV,30mA NST) system using a sloped primary where
>> the HEIGHT (ie included length) is adjustable while running.  This
>> would allow primary tuning, coincidental with coupling increase or
>> decrease.  Any help appreciated
>> 
>> Regards,
>> 
>> DAVE SHARPE, TCBOR
>
>Dave,
>
>Hope this is what you're looking for. Included are Archimedes, helical,
>and inverse conical primaries. The helical and Archimedes forms are from
>Wheeler, and the inverse conical is a hybrid form that appropriately
>weights the vertical and horizontal components of Helical and Archimedes
>inductances. 
>
>All dimensions are in inches, and L is in microHenries. While the
>Inverse Conical calculation is a little "hairier" than the first two,
>it's relatively easy to calculate for any desired angle, especially if
>set up in a spreadsheet. 

---------------  snip

>Case 3: Inverse Conical Primary:
>
>                                     
>                                    / \  
>    --  o                          /    o
>     |   o                        /    o
>     |    o   N turns            /    o
>           o                 Z  /    o
>     h      o                  /    o   /
>             o                /    o   /
>     |        o              /    o   /  Angle = X
>     |         o              \  o   /   
>    --          o               o    ------------
>                        |
>        |   w   |   R   | 
>                        |
>            |<--  W  -->| 
>                        ^
>                 Center | Line
>
>          Z = Coil Width (hypotenuse length)
>          X = Angle of Cone
>          h = Z*sin(X)  Effective vertical Height
>          w = Z*cos(X)  Effective horizontal Width        
>          W = R + w/2   Average horizontal Radius
>
>
>     L1 = W^2*N^2/(9*W+10*h)  (Vertical Inductance Component)
>
>     L2 = W^2*N^2/(8*W+11*w)  (Horizontal Inductance Component)
>
>      L = SQRT[(L1*Sin(X))^2 + (L2*cos(X))^2]  
>
>------------------------------------------------------------------------
>Safe coilin' to you, Dave! Hope to see you and Richard later this month!
>
>-- Bert --
>
>
>
>