Hi John,
I did a lot of reading about proximity effect in a number of old college
text books of mine
yesterday (who woulda thunk that this boring stuff would come in handy some
day?). The new
numbers I calculated are closer to yours than my 3/5.
I find the usual formula for the ratio of Rac/Rdc = d*sqrt(mu*f/rho) very
unsatisfactory for
small diameters, since as d gets smaller the ratio cannot get less than 1.
The same is true for >low values of frequency. Instead I use a couple of
series approximations to the Bessel
functions. So I checked your figures and found for AWG #12 at 185kHz, a
ratio of 3.6 and for #8 >a ratio of >5.56, quite close but slightly higher
than your figures.
The point you made is of course why it is better to use properly made Litz
wire to keep the
advantage of thicker wire.
Right. I'm still pondering what the spacing should be between two #12 Litz
wires to keep the proximity effect to <10%. I'm calculating something like
0.12" but this is much closer than originally thought. Does your math handle
this?
Thanks,
Bill A
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