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Re: Copper strap...



At 10:19 AM 03/04/2000 -0500, you wrote:
>For RF currents, like in your tank circuit, I would say this foil would be 
>closer in behavior to a 1 inch diameter copper pipe due to the surface area(I 
>didn't consider skin depth when making this statement).  But as far as your 
>equivalent diameter, I get the same answer.   I would hazard a guess that it 
>can handle more RMS power than the equivalent size solid round conductor 
>since it has more surface area for cooling.  
>Mike
>
>
>> Original Poster: "M Fabs" <the_machin_shin-at-hotmail-dot-com> 
>>  
>>  I recently got some (3) mil (I think) by 1.5" copper foil.  I was trying 
>to 
>>  figure out about what AWG number this would correspond to on Fr. Tom's 
>>  wirelist.  3mils * 1500mils gives 4500 mils.  Divide by pi, take sqrt, 
>>  multiply by 2, I get 75.6mils diameter for an equivalent circular area.  
>>  Look on the wirelist I see between 12 and 13AWG.  Is this right?  This 
>stuff 
>> 
>>  seems much more capable than that. Maybe I am remembering the thickness 
>>  incorrectly...
>>  
>>  MPF
>>  the_machin_shin-at-hotmail-dot-com
>

Hi Mike and MPF,

	RF currents flow on the outer surface of a conductor due to the skin
depth.  This distance depends on the frequency and type of material.  For
copper the skin depth is:

	D = 2.602 / SQRT(F)
where:
	
	D = Skin Depth in inches
	F = Frequency in Hz

So if we run at say 200kHz the depth of conduction is 0.0058 inches.  So
your copper strap is using all of it's area for conduction.  Since both
sides are active, you could have gone to 12 mil copper strap.

The area of copper is 1.5 x 0.003 = 0.0045 in^2 which would at first appear
to be equivalent to 13 or 14 gauge wire.  However the skin depth only
allows the outer 6 mil of wire to be conductive. Thus, you want wire that
has the outer 6 mil of area equal to your copper strap. Your wire really
needs a circumference of about 0.75 inches or a diameter of 0.24 inches.
That is close to 2 gauge wire which is the answer to your question (if i
didn't mess up ;-)).

Cheers,

	Terry