Re: More Coupling...

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <paul-at-abelian.demon.co.uk>

Barton B. Anderson, <tesla123-at-pacbell-dot-net> wrote:

> Example 1: ...

With secondaries, we would ideally like a count of turns. If we have
to estimate turns by whatever means, the utility of the measurement is
reduced.  This is the case with most secondaries, the exceptions being
those wound by machine. However, the accuracy wrt secondary inductance
is not an issue, so I'm quite happy to tune the turns value to match
(via Nagaoka) a low frequency inductance measurement.

...
> Of the coil data thus far, Marco's is mostly a guess as I don't have
> all the information.

The secondary inductance discrepancy is yet to be resolved. Does Marco
have considerable eddy loop coupling, or has he actually got fewer
turns than specified?

> With his coil, I did an actual inductance approximation (which no,
> we don't want to do) but I was missing a lot of information needed.

>From tssp records, I have for Thor:
        
Primary Coil Inside Diameter (IN) (wire center to wire center) 21.5750
Primary Coil Wire Diameter (IN)   0.3150
Primary Coil Wire Spacing (IN)  (NOT center to center) 0.8700
Primary Coil Number of Turns   9.5000
Height above ground  39.527"

Marco on his coupling measurements page reports 9 turns used, but
his inductance seems to be commensurate with the full 9.5

> Suggestions:
> * Measure ID and OD center to center of winding.
> * ID: Measure 2 points and average.
>         * Point 1: across start of winding.
>         * Point 2: move 90 deg from start and measure.
>         * Calc: (1 + 2)/2

The inner radius we're after is that between the axis and your
Point 1. By moving 90 deg from the start, the radius has increased
by pitch/4 and the 'Calc' value is then over-estimated by pitch/8.

> * OD: Same method as ID measurement, except:
>         * Point 1: Measure from tap point.
>         * Point 2: move 90 deg in from tap point and measure.
>         * Calc: (1 + 2)/2

Similarly Point 1 is desired outer radius, 'Calc' value is under-
estimated by pitch/8.
 
Why not measure from the start of the inner winding across the
axis to the diametrically opposite point, which is at a radius of
R1 + pitch/2, where R1 is the desired radius of the start of the
winding. Then your ruler is measuring 2R1 + pitch/2.

A similar thing for outer radius R2, the ruler gives 2R2 - pitch/2.

So take the inner diameter as Din, the outer as Dout, as measured
in the way I suggest, and you have

Din  = 2R1 + pitch/2
Dout = 2R2 - pitch/2

So

Dout + Din = 2(R2 + R1)
Dout - Din = 2(R2 - R1) - pitch

And noting that pitch = (R2 - R1)/N where N is turns, a little bit
of algebraic manipulation gives you a couple of nice formulae into
which you plug your ruler measurements to give R1 and R2.

Cheers,
--
Paul Nicholson,
Manchester, UK.
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