On 2/28/2019 1:05 PM, jimlux wrote:
Aluminum resistivity is 2.65, Copper is 1.68
Skin depth at 7MHz for AL is 30.97 micron, for Cu is 24.66 micron
So, resistance of a coil in Al vs Cu is = 2.65/1.68 * 24.66/30.97 = 1.26
It is simpler to just take the square root of 2.65/1.68 =
sqrt 1.58 = 1.26. It is not necessary to calculate the skin depth ratio,
which is also 1.26, not coincidentally.
Q of a Al coil would be 80% of the Q of a Copper coil.
So far correct.
Assuming the current in the coil is the same, the resistive power
dissipation in the Aluminum will be 60% higher.
Correction.
P = I^2*R, hence the aluminum coil dissipates 26% more heat than the
copper, not 60% If you past DC through the coil, that dissipation
will be 58% higher than if copper is used.
How hot the coil gets is not just 26% more, but depends on the
delta T, and the emmissivity of the respective coils. The
aluminum should ideally be black anodized, not shiny.
Rick N6RK
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