Rap 'n Tap
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From: John Davidson
Date: 11/8/00
Time: 1:23:18 PM
Remote Name: 206.16.140.254
Hi Gary, Well, I have what I think is a “vision” of what’s going on & its not quite “eddy current” oriented. Instead, I see the current in adjacent turns repelling because of basic “magnetism”, (or more precisely, effects of Special Relativity). This drives current away from conductor sides. Current in wires across the coil diameter attract the current toward the center axis of the coil.
You can see this if you hang parallel wires a quarter inch or so apart several feet long and allow them to swing mechanically. If you put current through them in the same direction, they repel. Current in opposite directions make the wires attract each other.
In a coil, the net result is that current favors the inside of the curve (where the windings touch the coil form) and doesn’t take advantage of all the copper in the coil. Pushing the windings closer together aggravates this, almost pinching off the current. Spreading the windings out a little sacrifices L a little but allows current flow more freely, reducing coil “resistance”, & raising net Q. (BTW, So far as I can tell, this appears independent of coil self capacitance.) Peak Q in solid windings seems to me to happen when wires are spaced about 60% of their diameter.
Litz is a bundle of fine enamel insulated wires usually wrapped with something (silk, Teflon tape, or something similar) to hold them together. Looks something like "stranded" wire, but not.
Litz “compartmentalizes” the conductor so that migration of the current flow to the inside center of the windings is prevented. Litz seems to bring features that both help and hurt Q, and you have to get the right Litz design to have a net increase of Q. _J_