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25th July 2004, 06:01 PM  #1 
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Join Date: Jun 2003
Location: Serbia

Air core inductors, calculations
Hi,
I need for the xover next air core inductors: 1mH  14ga wire 1.5mH  14ga wire 0.25mH  20ga wire I found on http://www.lalena.com/audio/calculator/inductor/ air core calculator but i don't know what is the best proportionratio between Coil Diameter and Coil Length. Please, can someone help me with this calculations? Just one hint, the inductor (finished) should be not to big in diameter. Thanks, Boban 
25th July 2004, 08:48 PM  #2 
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Nobody

25th July 2004, 09:22 PM  #3 
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Location: USA, MN

http://home.earthlink.net/~jimlux/hv/wheeler.htm
I am not sure where the lalena formula came from, although it appears to be a modified version of wheelers single layer formula. With the test coils I have made, the wheeler formulas are satisfactory. Shape does not appear to be a really sensitive factor for coils. I minimized the wheeler equation for lowest DCR and found one minima at 6*a = 9*b = 10*c , if I am recalling things correctly. Rather large deviations from this shape (that had the same inductance) did not appear to change DCR much... Some other equations specify that the inner radius of the windings should be equal to the length of the coil, ("b" in the equations below) The equations below are copied from the page in the link above, but they can also be found in the ARRL handbook and many other places..  L (uH) = 0.8 * a^2 * n^2 / (6*a + 9*b + 10*c ) where a = average radius of windings b = length of the coil c = difference between the outer and inner radii of the coil. all dimensions in inches. It states that it is accurate to 1% when the terms in the denominator are about equal. This is also an equation by Wheeler. It applies as long as the coil has a rectangular cross section.
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25th July 2004, 09:37 PM  #4 
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http://www.fnrf.science.cmu.ac.th/th...ed%20coil.html
Note that the link confirms the low sensitivity of shape, but gives you the answer you wanted.
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Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. Carl Sagan Armaments, universal debt, and planned obsolescencethose are the three pillars of Western prosperity. —Aldous Huxley 
26th July 2004, 10:44 AM  #5 
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Or you can go to http:\\www.solen.ca and check their inductors' size and dimension before plugging the numbers into the online calculator. Their dimension is computer optimized.

26th July 2004, 11:30 AM  #6 
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Great . Thanks.
Boban 
26th July 2004, 03:10 PM  #7 
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Location: Newcastle, Australia


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