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# Re: [femm] inductance

- To: femm@yahoogroups.com
- Subject: Re: [femm] inductance
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Tue, 13 Nov 2001 12:10:33 -0500
- Organization: Foster-Miller, Inc.
- References: <20011113151223.67096.qmail@web11405.mail.yahoo.com>

    Tomislav Borzic wrote:

    > Hello everybody, I am (again) coming with small
    > problem.
    > It is about inductance. I am callculating inductance
    > of a coil.
    > 1. one turn
    > 2. four turns.
    >
    > In case (1) I use formula L= (mi0/pi)*(1/4 + ln(D/r0)
    > where is: mi0=4*pi*e-7
    > D- diameter of coil ( like this: 0-----D----0, where 0
    > is
    > conductor and D is space between them)
    > r0= radius of conductor
    >
    > I know this is formula for two paralell conductors and
    > inductance
    > between them but with some assumptions it can work.
    > so in this case, r0=0.05m, D=0.8m,I+ = 1A, I-=-1A,
    > my callculations give 1.2 e-6 H/m, FEMM 1.16 e-6 H/m,
    > so it is ok.
    > I used AJ block integral (A j dV/2 = energy)
    > BUT, if I take four turns of wire, inductance should
    > be 16 times
    > higher because inductance of coil rises with n^2.
    > (n = number of turns)
    > I can not achieve acceptable solution.
    >
    > *.fem file is attached.
    > plase help
    > thanks
    > tomislav.
    >

    I think that the trick here is that you've assigned the same "circuit" property to all four turns.
    If you do this, 1/4 of the current is carried by each turn, so the current that you need to use in
    your calculation is 0.25A for the four-turn case. If you do this, the answer seems reasonable--not
    exactly 16 times the single-wire case, because the geometry is different, but in that ballpark.

    >
    > P.s. (to david) nearly done with translation.
    > how to create *.pdf?
    >

    Well, there are at least 3 options:

    1) Use the TOM Document Conversion Server at
    http://wheel.compose.cs.cmu.edu:8001/cgi-bin/browse/objweb It seems to do a good job at converting
    just about any file format to pdf for free.

    2) Get Ghostscript at http://www.cs.wisc.edu/~ghost/index.html You use a Postscript printer driver
    to save a postscript printout of your document to disk; you then use ghostscript to convert the
    postscript into pdf. It's possible to set it up so that things act just like the pdfwriter print
    driver. The down-side of this approach is that it can be very difficult to get everything set up
    right in the first place.

    3) Just email your document to me personally. I own the pdfwriter print driver, and I also have
    ghostscript installed, so I can do the conversion.

    Dave

    begin:vcard
    n:Meeker;David
    tel;fax:781-890-3489
    tel;work:781-684-4070
    x-mozilla-html:TRUE
    url:http://members.aol.com/_ht_a/dcm3c
    org:Foster-Miller, Inc.;Electrical and Electronic Systems Group
    version:2.1
    email;internet:dmeeker@foster-miller.com
    title:Senior Engineer
    adr;quoted-printable:;;350 Second Avenue=0D=0A;Waltham;MA;02451-1196;USA
    fn:David Meeker, Ph.D.
    end:vcard

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- References:
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    - From: Tomislav Borzic <tborzic@yahoo.com>

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