MiscEl: Air coil

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This page is used to calculate different types of air coils. For best result always use the formulas without (...) after.

The basic formula to calculate inductance is: inductance=permability*turns*turns*area/length, the problem is that the result are not very exact when compared to a real coil. To give results that are closer to real world values some other formulas was made (Wheeler, Blakey) for specific coil geometries. They are simple and give better results than the basic formular. But even better formulas has been made, they are not simple, but the result are usual very close to the correct value (This program are using these formulas).

Geometries supported

All names with (...) after has lower precision or some restrictions.
When the graphic shows two yellow squares, one is a look from the end of the coil, but without the turns illustrated.

Input values

TurnsNumber of turns on coil
LengthLength of coil
Diameter ØminInner diameter of coil
Diameter ØmaxOuter diameter of coil
Wire diameterWire diameter, use Wires page to convert units
Bundle diameterDiameter of wire bundle on a "circular loop" coil
SideOne of the sides on a square/rectangular coil
Side 2The other side on rectangular coils
Winding thicknessThickess of winding layer
FrequenceFrequence used on coil/wire, used to compensate for skin effect
Fill factorDefines how tight the wire is wound (100 means no space for air or isolation)
Note: All measurement inputs, except wire diameter, are in meters.

Output values

InductanceThe estimated inductance, the error is depending on formula, how exact the coil is constructed, any iron in the vicinity and frequence
Coil lengthLenght of coil, this is the same value as the input value "Length"
Avg. coil diameterAverage diameter, this is diameter_Ømin+winding_thickess
Avg. sideAverage side, this is side+thickess of copper
Avg. side 2As above, but for long side on rectangles
Winding thicknessThe thickness of the windings
Wire lengthTotal length of wire use for this coil
ResistanceResistance in wire
Estimated weightWeight of wire

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