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# Re: [FEMM] Modeling multiple turn coils

- To: Finite Element Method Magnetics mailing list <femm@list.foster-miller.net>
- Subject: Re: [FEMM] Modeling multiple turn coils
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Wed, 22 Oct 2003 21:12:45 -0400
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`Scott wrote:`

> `I use FEMM to model loudspeaker motors and coils. Until now, I modeled coils as a single, non-conductive
> cross-section with a current numerically equal to the
> number of turns (I model them as non-conductive to
> eliminate Hall effects that wouldn't be present in
> real coils). In these cases,I believe the Lorentz
> force is numerically equal to the ubiquitous speaker
> parameter "BL".`

>     To investigate this simplification I created two
>     models:  one with the single cross-section I described
>     above, and one with the cross-section divided into 50
>     smaller sections/blocks (to simulate 50 turns).  In
>     the first case there is one material property marker
>     assigned to a circuit with 5 Amps; in the second case
>     there are 50 separate property markers, each assigned
>     to a circuit with 0.1 Amp (5 total Amp-turns in both
>     cases).

> `My confusion: I expected similar results, but found
> them very different. Moreover, I found that I could
> get identical results if I use equal circuit currents
> in both models, regardless of how many sections in
> which the coil was divided. Is there an error in my
> methodology for modeling turns explicitly/implicitly? I didn't find anything enlightening by searching prior
> messages....`

>     Thanks,
>     Scott

`The "circuit properties" connect all of the regions marked with a particular circuit property in parallel. That's why you get the same result for your problem regardless of the number of pieces--the total amp*turns carried by the coil is the number defined as the current in the "circuit property."`
`I know the "circuits" thing can be confusing--I'd originally intended it merely to enforce current constraints in solid regions in eddy current problems. I'm working on adding a series-connected circuit property and adding turns as extra block label attribute so that assigning the currents in multi-turn coils will be a bit more natural.`
`Dave.`
`--
David Meeker
Senior Engineer
Foster-Miller, Inc.
350 Second Avenue
Waltham, MA 02451-1196
781-684-4070
781-890-3489 (fax)
dmeeker@foster-miller.com`
``

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- References:
  - [FEMM] Modeling multiple turn coils
    - From: Scott <shanteserve@yahoo.com>

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