Need help with a branch current assigment.

Discussion in 'Homework Help' started by Bombasa, Dec 2, 2012.

1. Bombasa Thread Starter New Member

Dec 2, 2012
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E3 is confusing me. I could ''easily'' solve it if it wasnt for the voltage source E3.

the assigment is to find I1, I2 and I3 using the branch current method.
I got this so far using KVL:

E1=-R1*I1 - R3*I3
E2=-R2*I2 - R3*I3

I dont know where to put E3 at all. help me?

2. bonshie New Member

Nov 21, 2012
4
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Hi Bombasa.Is there any specific law that we need to use for this cicuit?Or we just use any law just to find the current I1,I2 & I3?

Dec 2, 2012
8
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4. WBahn Moderator

Mar 31, 2012
23,089
6,941
The Branch Current Method (a less formalized version of Node Voltage Analysis) is primarily the application of KCL, not KVL (though KVL often plays a supporting role).

It's hard to evaluate your equations because you haven't bothered to tell us how you have defined your currents (which branch and which direction). We are not mind readers. Yes, we can probably figure it out from your equations, but (1) we shouldn't have to -- it IS your problem, after all, and (2) that might be where your problem is and if we back it out, then we run the risk of us talking about one thing and you talking about another.

You have five nodes in this problem. Do you see them all? Don't forget to include the node at the bottom. Now, you get to arbitrarily define one of these nodes as being 0V (or ground) -- though this is already done for you in this particular problem. This leaves you with the voltages on four nodes to figure out. Label the four nodes something -- it doesn't matter what, but give each of them a name (using numbers or letters is the most common). Now see if any of the node voltages can be solved for directly. Hint, in this case you can solve immediately for three of them. This will leave you with one node voltage to solve for. Specify the name and direction of each branch current that connects to that node. Now write the branch currents in terms of the unknown voltage, the resistors in each branch, and the known voltage on the other side of each of those resistors.

If you need to use KVL, then you probably should be using the Loop Current Method (which will later be formalized as Mesh Current Analysis).