Mesh current issue

Discussion in 'Homework Help' started by Xmetalfanx, Aug 24, 2013.

  1. Xmetalfanx

    Thread Starter New Member

    Aug 23, 2013
    (first I want to say that I am having issues searching the forum, so if this has been answered already, i am sorry for re-posting a question someone else asked)... and too the admins... I tried submitting this on Firefox, though i came up with a blank page after i hit submit .... bottom line is I am sorry if this was submitted a few times (I cant tell) .. that was not my intent

    I am a hobbyist I guess you can say and am self-learning a number of topics, and this is not an urgent question, though I have been trying to see where I am going wrong for some time now, and its like "staring at a cross-word puzzle".

    Anyway, as far as the actual problem/question: is a summary on my site of what is going on, though I can say (even before anyone would click that link) that it has to do with Mesh current with 4 mesh, the center two meshes have a voltage source between them and the outer two have current sources.

    I thought I had a "decent" (though as the instructor i have been following says .. "do alot of example" to really get the hang of it) grasp on this, though this is messing me up for some reason.

    I have been staring at this problem so long, trying not to ask for help and figure it out myself, though I have (figuring it out without asking anyone for any help) thrown in the towel and admitted I need a "point in the right direction".

    My Guess though somehow I can not seem to get the correct answer in the end, would be A) Take IA and ID and subsitute those values into the mesh iB and mesh iC equations (accordingly) and to then use the matrix method to (that is the way my instructor would probably do it) get iB and iC

    I can not thank anyone who would take a look at this enough for the time and effort. Again, I am not in any formal classes at the moment, though this problem has been driving me nuts and I have not had my "ah ha!, that's how you do it" moment yet.

    Thank you again,
  2. Xmetalfanx

    Thread Starter New Member

    Aug 23, 2013
    ok i figured it out (why i couldn't post) .. it had to do with the bug apparently of Titles over a certain number of characters long. I just didn't want to submit the question/post a number of times and the admins get upset as if i was "trying to spam" the forum. sorry about that.
  3. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    It can be confusing to a beginner using the mesh method when he first encounters a mesh with a current source in it rather than a voltage source, or no source at all. You don't know what the voltage across the current source is.

    You could convert IS1 and R1 into their Thevenin equivalent; then you would have a voltage source.

    But, the easiest thing to do is to realize that instead of trying to write the usual equation for the voltage drops around the mesh, you can just write a "constraint" equation. When there is a current source all by itself, not sharing a branch of another mesh, the current in that mesh can't be anything other than the value of the current source itself.

    So the equation for mesh A can be iA = IS1, or iA = -.001

    Similarly, the equation for mesh D can be iD = .001

    Together with your two other equations, you now have 4 equations. Solve them and you have your answer.