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# Re: Inductance using FEMM

- To: femm@yahoogroups.com
- Subject: Re: Inductance using FEMM
- From: jim271@hotmail.com
- Date: Sun, 18 Nov 2001 23:04:44 -0000
- In-reply-to: <000001c17048$3b544820$9dfc6f82@mrmosfet>
- User-agent: eGroups-EW/0.82

    Example of using FEMM to find the inductance of a coil with the
    dimensions and number of turns specified:

    Wire gauge = 18AWG
    Max current goal = 100 Amps.
    Voltage = 340 V.

    Dimensions (using the MGC calculator):
    Length = 12 inches = 0.304m
    Inner radius = 0.156 inch
    Outer radius = 0.56 inch
    Coil thickness = 0.56-0.156 = 0.404inch = 0.0102m

    Cross sectional area of winding = 0.304*0.0102 =0.003101m^2

    Current = 88.4 Amps per turn
    (the current is less than the specified 100amps because the
    calculator assumes each layer of the coil is fully wound.)

    Number of turns = 3152

    Total current = 3152*88.4 = 278637 = 0.2786 MegAmps

    J = Current density = 0.2786/0.003101 = 89.8MA/m^2

    Use this value of J for the copper in your FEMM model.

    Run FEMM and highlight the copper, read integral(A.J)

    Inductance = integral(A.J)/(88.4*88.4)

    This should be pretty close to the value from the calculator (8.93mH)
    which was obtained using Wheeler's formula.

    -- Jim

- References:
  - Coil Dimensions
    - From: "Samuel Ace Winchenbach" <swinchen@eece.maine.edu>

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