Re: Flat secondary measurements

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

Original poster: "John Tomacic by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla_ownz_u-at-hotmail-dot-com>

Hi,

I used "Wintesla" to calculate the inductance of my 5.625 inch diameter 
coil, 21.9 inches long wound with #24 wire. It gives an inductance of 32.64 
mH, and length of wire 1478.55 feet.

For the flat spiral I used the following formula for inductance:
L= (NR)^2/(8R+11W) N= 431 turns, R=6.55 (inside radius = 2 in, outside 
radius = 11.1 inches) and W= 9.1 in (431 turns * 0.0211 (wire dia)).

L= 52.28 mH

The wire length in the spiral was calculated from
lenght = N*pi*(2*r0+d*N)/12   N= 431 turns, r0 = 2 inches (inside radius), d 
= .0211 (wire diameter), pi = 3.14159

l= 1478.40 feet

Regards,
John T.

>
>John Tomacic wrote:
> > Surprisingly, the inductance of the flat spiral coil is 60% higher
> > for the same length of wire. In this case the length of wire is
> > 1478 feet.
>
>Interesting.  I've always assumed that a flat spiral would have less
>inductance than the same length of wire wound into a solenoid. But
>I've just run some numbers through acmi,
>
>flat {
>    radius1 0.01
>    radius2 0.50
>    height 0
>    conductor 0.5 mm ; radius
>    turns 392
>}
>
>helix {
>    radius 0.25
>    height1 0
>    height2 0.49
>    conductor 0.5 mm ; radius
>    turns 392
>}
>
>(the 392 turns chosen to give 0.8 spacing ratio with 1mm diam wire
>  over a 49cm winding)
>
>Both require about 25cm x 2 pi x 392 centimetres of wire, but
>we get
>
>   Flat           Helical
>
>L 55.7 mH        52.9 mH
>R 13.99 ohms     13.72 ohms.
>
>So not as much as your 60%, but still an increase, which is not what
>I would have guessed.   John, can you let us know your coil
>dimensions and measurements that lead you to that amazing 60% ?
>
> > Since the wire resistance is the same for both coils,
> > is it safe to conclude that the Q of the spiral would be 60% higher
> > seeing that Q is proportional to XL/R?
>
>That would be nice!  But the proximity effect will interfere with
>that increase, in a way that I don't know how to calculate.
>
>Could the experts with the inductance formulae please check my flat
>spiral calcs for sanity?
>
>Cheers,
>--
>Paul Nicholson
>--
>
>
>


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