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:

> Checked the meter today against a scope at work. If there was a
> discrepency, I couldn't see it. Also checked it against 2 other
> calibrated DMM's = Idetical (wow, good calibration). So I figured
> the meter is reading correctly.

Yep, can't argue with that. 

> I was tapped at 10.6 turns, not 11.6.

Well that takes a good bite out of the discrepancy - well spotted.

> Well, I retapped to 11.6 turns and decided to set up and go through
> the test again. Still had 1 DMM so checked current at +2, 0, and -2.
> The current was holding well at 10.07V (hair dryer).

OK. The current is remaining constant.

> Update to your previous example,
>       bart     acmi    error%
> +2    0.135    0.141    4.44%
>  0    0.165    0.178    7.88%
> -2    0.195    0.215   10.26%

Bart, I can no longer find any reason to doubt your V/I readings,
and your dimensions are unlikely to be out by far enough to account
for the 10% error.

I've made a slight alteration to acmi. It represents the spiral as
concentric circles and the circle radii were set to the inner
radius of each turn of the spiral. I've now set the radii to the
mean radius of each turn, which has increased the primary inductance
predictions a little, and lowered the k. I now get for the two coils

Bert   161.8 uH  73.5 mH             0.209    15.625 turns on pri
acmi   174.8 uH  74.1 mH  702.9 uH   0.195    16 turns on pri
error   +8.0 %   +0.8 %             -6.7 %

Bart+2 107.1 uH  87.6 mH  601.1 uH   0.195    11.6 turns on pri
acmi   113.0 uH  87.5 mH  656.0 uH   0.209    12 turns on pri
        +5.5 %   -0.1 %    +9.1 %    +7.2%

Bart-2 107.1 uH  87.6 mH  416.7 uH   0.135    11.6 turns on pri
acmi   113.0 uH  87.5 mH  438.5 uH   0.140    12 turns on pri
        +5.5 %   -0.1 %    +5.2 %    +3.7%

Bart, with your alterations raising your k and my alterations lowering
predicted k, the two have converged from 17.5% to +7.2% error. I think
we're homing in on the limits of acmi here. It appears that acmi errs
on the high side up to +10% for self inductance of flat spiral
primaries.  Secondary inductance is about right, as expected. 
Error on k factor is say +/-10% and the trend for worse error at the
higher k factors remains.

The only way to take this further is with more results from other
sources. If a systematic error develops, either it can be calibrated
out of acmi, or I can do something smarter with the current filaments.

> Maybe if I've been nice (vs. nauty) this year, Santa will bring me
> an LCR and further verify inductances.

A measurement of the primary inductance would be of interest, but I'll
be surprised if its far from 107 uH. I can't suggest any further
refinement to your measurements and I think your readings now are
likely to be more correct that acmi.

I'll update the acmi web page accordingly in the next few days.

Cheers,
--
Paul Nicholson,
Manchester, UK.
--