Re: Barts Flat Coil Dimensions Was: Dimensions of my flat spiral coil

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

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

David,

If each of your three strands wraps the axis of the coil 224
times, then this is the number of turns you must use when
calculating L.  And the conductor radius should be that of a
single strand, not that of the trifilar bundle.

With this, I get

units inches
secondary {

   radius1 1/4/2     ;  Core is a 1/4" brass bolt
   radius2 13.75/2   ;  Outer diameter of 13.75"

   height 0

   conductor 21 awg
   turns 224
}

    SCNY.L| SCNY.R
6314.10 uH|   5.33

And I believe you are reporting 6.2 ish on all three.  I'm happy
with that.  Cross check by measuring the winding resistance.

Your three strands I believe terminate on the rim at 120
degree intervals, so therefore we have, say,

units inches
strand1 {

   radius1 1/4/2     ;  Core is a 1/4" brass bolt
   radius2 13.75/2   ;  Outer diameter of 13.75"
   height 0 conductor 21 awg

   turns 224 - 1/3
}
strand2 {

   radius1 1/4/2     ;  Core is a 1/4" brass bolt
   radius2 13.75/2   ;  Outer diameter of 13.75"
   height 0 conductor 21 awg

   turns 224
}
strand3 {

   radius1 1/4/2     ;  Core is a 1/4" brass bolt
   radius2 13.75/2   ;  Outer diameter of 13.75"
   height 0 conductor 21 awg

   turns 224 + 1/3
}

giving

    STR1.L| STR1.R|    STR2.L| STR2.R|    STR3.L| STR3.R
6295.32 uH|   5.33|6314.10 uH|   5.33|6332.90 uH|   5.34

Compare with your recently posted measurements...

    STR1.L|            STR2.L             STR3.L
6200 uH            6230 uH            6250 uH

I'd say you're seeing roughly the expected change in inductance
due to the extra 1/3 more or less of turns. The overall error
of, say (6.1 - 6.23)/6.23 = around -2% is quite reasonable. acmi
is only about 1% accurate, and your LCR meter would be about the
same at best.  So circa 2% is quite a satisfactory comparison.
--
Paul Nicholson
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