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Re: AC coil resistance equation




From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>

A further thought:

<snip>
> > 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
> 
> I used the measured figure for Q of one of my coils (300),back 
> calculated to find Rac (136 Ohms) and then used that as a substitute 
> for 3.2*Rdc in your equation. I guessed that d^2*fo should be divided 
> by 124 before taking log base 10. I got an answer of 786 which is 
> about 2* what it should be. I think your 3.2*Rdc figure doesn't take 
> turn-turn proximity effect into account. I was impressed nonetheless.

The coil is actually spacewound so the proximity effect probably 
isn't that significant. What might well be is the former (thickwall 
PVC drainpipe). I guess your formula might come close for an airwound 
coil. I should test it on a thinwall PE coil sometime. Source 
impedance was about 7 Ohms at the frequency of interest (146kHz).

Malcolm