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Homework Help: Mesh Analyses Problem

  1. Aug 22, 2011 #1
    1. The problem statement, all variables and given/known data

    [PLAIN]http://img718.imageshack.us/img718/3519/circuith.png [Broken]

    This is a circuit I've simulated in pSpice, I can't get the currents to match up with my hand calculations using mesh analyses. Specifically, I'm not entirely sure how to handle the current source.

    2. Relevant equations

    Mesh 1 is far left, mesh 2 is the center and mesh the is the far right.

    Mesh 1.

    [itex]18 = 15i_{1} + 30(i_{1} - i_{2})[/itex]

    Mesh 2.

    [itex] 0 = 10i_{2} + 20(i_{2} - i_{3}) + 30(i_{2} - i_{1})[/itex]

    Mesh 3.

    [itex] 30 = 40i_{3} + 20(i_{3} - i_{2}) [/itex]

    finally, putting all this in a matrix ( I'm using an online calculator, to eliminate the possibility of an error here, but I do know how to do it by hand ).

    I get,

    i_{1} = 0.407A
    i_{2} = 0.010A
    i_{3} =-0.580A

    Thanks :smile:
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Aug 22, 2011 #2


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    Staff: Mentor

    For the 10Ω resistor term in the second mesh, include the current of the current source as though it were another mesh's current. Thus
    [tex]0 = 10(i_{2} - I1) + 20(i_{2} - i_{3}) + 30(i_{2} - i_{1}) [/tex]
    where I1 is the value of the current source.
  4. Aug 22, 2011 #3
    Thanks for the reply, however I managed to solve the circuit just a few minutes after I posted it.

    I realized that I've been looking at this whole mesh analyses technique the wrong way.

    A huge 'lightbulb' moment. Feels good man.

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