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Re: AC coil resistance equation


-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, August 28, 1998 7:21 AM
Subject: Re: AC coil resistance equation


>Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>
>
>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
>
>
>
Find inductance at 146KHz, if Xl = 7 ohms

7/(2 pi) = 1.114

1.114/146KHz = 7.631E-6


Find capacitor that is resonant at the frequency of 146KHz using a coil with
an inductance of 7.631 uH.

1/146KHz = 6.849E-6

6.849E-6/2 pi = 1.090E-6

1.090E-6 Squared = 1.188E-12

1.188E-12/7.631 uH = 0.1557 uF

To find the current required to operate the primary at the maximum peak
voltage.

Vs/(.5 * Xl[primary's AC resistance at the given frequency.])

Your circuit 3.5 ohms output impeadance 1000v supply/3.5 ohms = 285.7
Amperes, or
V*I = P in watts  285,700 watts.

Double the frequecy, and half the power.