help with mesh currents :(

Discussion in 'Homework Help' started by lp84, Jan 31, 2009.

  1. lp84

    Thread Starter New Member

    May 7, 2007
    4
    0
    Ive always had trouble with mesh current method for some reason, I was following the all about circuits page http://www.allaboutcircuits.com/vol_1/chpt_10/3.html And reading how setting the current directions were arbitrary. So I re-tried the problem for the wheatstone bridge basically using completely random current directions, and I could not get the mesh currents to equal the same as the answer at the bottom of the page

    heres a scan of my sign conventions/equations

    Can someone please tell me what im doing wrong? id really appreciate it.
    thanks
     
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,283
    326
    The first thing I see that's wrong is in the first equation.

    You have:

    150(I1+I3) + 50 I1 + 100(I1-I3) = 0

    but it should be:

    150(I1+I3) + 50 I1 + 100(I1-I2) = 0

    For the second equation you have:

    300(I2-I3) + 100(I2-I1) + 250 I2 = 0

    but it should be:

    300(I2+I3) + 100(I2-I1) + 250 I2 = 0

    After collecting terms for the second equation, you have a term 550 I2; it should be 650 I2.
     
  3. lp84

    Thread Starter New Member

    May 7, 2007
    4
    0
    ooh! thanks !
     
Loading...