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Re: Barts Flat Coil Dimensions Was: Dimensions of my flat spiral coil
Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
Dave Thomson wrote:
> The 224 is the number of wires one would count from the center of
> the coil along the radius. But each wire only makes 74.6 turns.
> 3 wires times 74.6 turns yields the number of wire counts along
> the radius.
Ok, that's clear now. I assumed the three strands were layed
together across the thickness of the spiral.
We have, roughly, for each strand,
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
700.31 uH| 1.78
As you can see, your measured inductance is much higher than we
would expect, 6230/700 = 8.9, almost exactly 9 times higher!
We would expect almost 9 times higher if you wired all three windings
in series (choosing polarity to ensure all currents circulate in the
same direction). When you measure each strand, are the other two
So there's definately something awry here. Either your measurements
are screwy, or there's some significance to the fact that your
measured inductance for each strand is equal (within experimental
limits?) to the expected total series inductance of the three (which
is the same as that of a single 224 turn winding).
Can you measure the resistance of the windings, see if they are
each around 1.8 ohms? While you are at it, check for shorts
between the three strands.
Now for an interesting test: Wire your three strands in series,
so that they all add. If the 6.23mH you are measuring on each
strand is real and independent of the others, then maybe you will
get around 9 times *this* when they are in series!
It'll be interesting to see the results from some 60Hz inductance
measurements, if you can pull them off.
> Could it be that three wires tightly coupled and wound in parallel
> act as one single continuous wire?
It shouldn't be. Each strand should give the predicted inductance,
so long as the other two are open-circuit. We need to get to the
bottom of this.