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Re: AC coil resistance equation
From: "James" <elgersmad-at-email.msn-dot-com>
I thought the AC resistance equation for coils was 2 pi freq(in Hertz) H(in
Henrys).
>From: "bmack" <bmack-at-frontiernet-dot-net>
>
>Hello all
>
>I haven't been very active on the list of late, so I thought now is as
>good time as any to participate.
>
>A few months ago I wanted to calculate the unloaded Q of my coils,
>but had no equation to find the AC resistance. The only thing I could
>readily find was a passage in the 1995 ARRL handbook that states
>that the starting frequency for skin effect has the relationship
>f = 124/d^2. Where f is frequency in MHZ, and d is the wire diameter in
>mills.
> This in itself is pretty much useless, but then they state
>( I paraphrase for clarity):" the ac resistance increases by about a factor
>of
>ten for every two orders of magnitude". Or another way is to say each
>order of magnitude increases the over the dc resistance by a factor of
>sqrt(10) which is approx 3.2.
>
>Therefore AC resistance has the relation
>
>Rac=3.2*Rdc(log fo/fc). fo is the operating frequency, and fc is the
>skin
>effect frequency, both in MHZ.
>
>Now I substitute fc since fc=124/d^2
>
>resulting in Rac= 3.2*Rdc*(log (d^2 *fo)/124)
>
>d= wire diameter in mills
>fo= operating frequency in MHZ
>Rdc= coil dc resistance
>
>At least this way the math is a single step affair and the logarithmn
>povides an accurate magnitude calculation.
>Did I help anyone or did I just reinvent the wheel?
>
>Jim McVey
>
>
>