Coil Calculator

[radioacoustick]

I would like to fix "The world's simplest coil calculator". Inductance isn't proportional to circumference of the coil but proportional to its area. If we try to transform the circle to ellipse then inductance will be decreased (area also) but circumference will be the same. Therefore we can modify the world's simplest coil calculator formula as follow:
L = k*S*N^2
S - the area of the coil;
N - number of turns;
k - inductance factor, that can be measured by the testing coil with a few number of turns;
This is also not perfect estimation certainly, but allows more exatly getting into the "right ballpark".

[Skippy]

From my experience and experiments, it's not proportional to area. Clearly you have a point - if a coil was squashed so long and thin it was basically a straight line, then inductance would be severely reduced, to a few percent of the full round value. But for practical detector coils, where an elliptic loop is not going to be much more than length:width ratio of 2:1, the 'area-related' formula is too severe. A few practical experiments, re-shaping a circular coil into ellipses, suggests that even a 2:1 ratio coil has 95% of the inductance of the circle, whereas using an 'area-related' formula would suggest the inductance would drop to approx 80% of the circular value.

I personally tackle elliptic & similar shapes by measuring the circumference, then calculating the equivalent circular-plan coil size. I use the (Wheeler-based) calculator to determine specifications, but aim for an inductance 2% - 4% higher than required, to allow for the corresponding drop when shaped to an ellipse.

[green]

http://www.geotech1.com/forums/showt...116#post192116

I posted a coil I made awhile back in above reply. Same circumference, different shapes. 80.6 in. sq., 67.1 in. sq., 55.6 in. sq.

[Dave J.]

Skippy's right.
If the maximum dimension of the cross-section of the wire bundle is extremely small relative to the distance from one side of the coil to the other, the shape of the coil (even if 3-dimensional or figure- becomes irrelevant. An alternative "simplest" computation is to divide the total length of wire in the winding (in meters) by the number of turns, multiply that by 1.3 uH, and multiply the result by the square of the number of turns. This approach asks no questions about shape or subtended area, only "circumference".

[radioacoustick]

Yes, I understood my mistake. Inductance is nearly proportional to area in case of long solenoid. But in case of a single turn the inductance is nearly proportional to its circumference. If the coil is the wire bundle with relatively small cross-section (relative to dimensions of coil), it can be represented as a multi-winding solid "single" turn with the similar properties.

[vbeeeks]

Can anyone download NASA s/w at <https://software.nasa.gov/software/KSC-12253> just want to check the claims.

[Gwil]

To find the inductance of a non-circular coil find its area (draw full size on graph paper and count the squares), calculate the radius of the circle with the same area, and enter this radius into Qiaozhi's calculator.
Works for me.

[Qiaozhi]

Personally I find that a more accurate result is obtained if you simply take the two diameters, add them together, and then divide by 4. Enter this value for the radius into the Coil Calculator.