Re: surface area of wire

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

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: "chris swinson" <exxos-at-cps-games.co.uk>
 >
 > Hi all,
 >
 > I'm considering winding a small test coil with litz wire. I would like to
 > know if theres a chart which states the skin depth of wire at high frequency
 > in mm. Ive seen a chart in inches floating around though I can only get to
 > grips with mm. From what ive found 200khz is around 0.15mm skin depth. It
 > would be useful to have exact figures.
 >
 > Also, Is there any comparrisons to surface area in relation to solid
 > core,multistrand and litz wire ? For example if I have a wire of 1mm dia,
 > surface area would say be 3mm, now if I had a 1mm Dia wire with multistrand
 > how would that be worked out ? All the wires are shorintg out in all
 > combinations so in comparrison to the solid core wire I wouldn't imagine
 > multistrand to give much more surface area than solid core ?
 >
 > Litz wire would be the best. I plan to build a high Q secondary with this
 > wire to see what happens. I have compaired solid core to stranded wire and
 > was amazed to find the multistrand coil gave 2" arcs with little input
 > power, though a solid wire which should have been better , wasn't and gave
 > no output at all. Despite the stranded wire had spaced turns ( due to
 > insualtion ) there should be a lot less output since the solid core verson
 > was a normal wound secondary. Length of wire and wire dia was as close as I
 > could get.
 >
 > I think it would make a interesting test since multistrand worked better
 > than solid wire. which is why im interested in testing out Litz wire which
 > would give me 10times the surface area and should give a much higher Q coil.
 >
 > Many thanks,
 > Chris

	About thirty years ago I wound a coil (5.25" dia x 18" long) with litz
equivalent to #28 B&S. I couldn't tell the difference between it and a
similar form wound with #28, except that because of the cloth covering
of the litz I didn't get as many turns on it as I with the heavy formvar
wire and the frequency came out slightly higher.  Definitely not worth
the bother, at least in my opinion.  Remember that once the streamers
start to Q goes so low that wire resistance isn't very important.

Ed