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# RE: [FEMM] Unexpected inductances values!

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- Subject: RE: [FEMM] Unexpected inductances values!
- From: "Jiri Vecerka" <vecerkajiri@seznam.cz>
- Date: Mon, 10 May 2004 14:25:43 +0200
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    Hi

    I think, that you shold remove magnets (to set Hc to 0) if you use integral
    A.J.

    JV

    > -----Original Message-----
    > From: femm-bounces@list.foster-miller.net
    > [mailto:femm-bounces@list.foster-miller.net]On Behalf Of Ahmad Eid
    > Sent: Monday, May 10, 2004 8:57 AM
    > To: femm@list.foster-miller.net
    > Subject: [FEMM] Unexpected inductances values!
    >
    >
    > Dear all
    >
    > I'm trying to find the inductances (self and mutual)
    > of four coils PM linear motor.
    > I tried to folow the method that Dr David writes in
    > the manual, but I confused. If there are PM in the
    > design, I calculate the inductance with existing PM or
    > I should remove them first to calculate the
    > inductances.
    >
    > My calculations as follows:
    > I applied 10 A in the fist coil only and each coil has
    > 60 turns and using block integral and I don't remove
    > the permanent magnets from the model:
    >
    > 1) the self inductance of coil 1 = integral (A.J) dv =
    > -0.883457 Henry Amp^2 then dividing by current square:
    >
    > 	Lself = 8.8345 mH
    >
    > 2) the mutual inductance between coil 1 and 2
    >  	L12 = integral (A)dv
    > Integral of A over selection:
    > 7.8108e-007 Henry Amp meter^2
    > Integral of A / selected area:
    > 0.00150133 Henry Amp
    >
    > L12 = 0.00150133 *Nturns/current=0.00150133*60/10 = 9
    > mH
    >
    > 3) L13 = L12 = integral (A)dv
    > Integral of A over selection:
    > -7.55774e-007 Henry Amp meter^2
    > Integral of A / selected area:
    > -0.00145268 Henry Amp
    >
    > L13 = -0.00145268*60/10 = 8.716 mH
    >
    > 4) L14 =  L12 = integral (A)dv
    >
    > Integral of A over selection:
    > 9.24499e-007 Henry Amp meter^2
    > Integral of A / selected area:
    > 0.00177699 Henry Amp
    >
    > L14 = 0.00177699 *60/10 = 10.66194 mH
    >
    > As shwon from the four results that the mutual
    > inductance is bigger than the self inductance and I
    > think this is wrong.
    >
    > I don't know where are the mistakes
    >
    > any suggestion will be appreciated
    > thanks all
    >
    > ahmad
    >
    >
    >
    >
    >
    >
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- References:
  - [FEMM] Unexpected inductances values!
    - From: Ahmad Eid <ahmad_m_eid@yahoo.com>

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