# Re: Skin Effect

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From: 	John H. Couture[SMTP:couturejh-at-worldnet.att-dot-net]
Sent: 	Tuesday, August 05, 1997 2:48 AM
To: 	Tesla List
Subject: 	Re: Skin Effect

At 04:00 AM 8/4/97 +0000, you wrote:
>
>From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
>Sent: 	Sunday, August 03, 1997 4:28 PM
>To: 	tesla-at-pupman-dot-com
>Subject: 	Re: Skin Effect
>
>Hi Robert,
>          If I might comment also....
>
>> From:   Robert Davis[SMTP:RE.Davis-at-btinternet-dot-com]
>> Sent:   Sunday, August 03, 1997 9:27 AM
>> To:     'Tesla List'
>> Subject:    RE: Skin Effect
>>
>>
>>
>> Dear DR.RESONANCE,
>>
>> Sorry the calculation was not clear.  I used the X as multiplication.
>> In the second calculation for effective wire resistance the skin depth
>> term varies with frequency.  Also the lower case r was a typing
>> mistake.  The ^ symbol meaning, to the power of.  The 66 in the first
>> formula becomes 0.066 after converting skin depth in mm to meters.
>> The full equation is given below (without multiplication symbols)
>> after substituting the first formula for the skin depth term:
>>
>> Dynamic Resistance = L/C((PiR^2)-(Pi(R-(0.066/sqrt(F)))^2))
>>
>> Where:
>>     F = Frequency (Hz)
>>     L = Length of wire (m)
>>     R = Radius of Conductor (m)
>>     C = Conductivity of copper = 5.8 x 10^7
>>     Pi = 3.1415927
>>
>> In the above I use sqrt() as the square root function.
>
>Firstly, 66/sqrt(f) gives the skin depth in mm at frequency f for
>copper or at least one grade of it. Resistivity/conductivity is
>already factored into this equation. Seems superfluous to use it
>twice?
>
>Malcolm
>
>---------------------------------------------------------------------------

Robert -

You can also use                 D = 2.6/sqrt(F)
Where D = Depth in mils
F = Frequency in megahertz

Example for copper at 500 KHZ

D = 2.6/sqrt(.5) = 3.7 mils

From the Tesla Coil Construction Guide

John Couture

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