Determine current and voltage using Node Voltage method

[Daeol]

[Mod note: Post moved to new thread, so template not included]

Hello there again!

I started working on the second problem but I think I am doing it wrong so I thought I would post the first step and do this one step at a time to see where the mistake was.

So the task is to determine UR3 and IR3 using the Node-Voltage method. Also I hope it is not an issue that I am posting this here, I thought it would be better than creating a new thread.

This is the circuit:

So first thing I did is that I determined the currents that flow through the nodes A B and C.

A: I1 + IR2 - IR1 - IR3 = 0
B: IR3 + I2 - IR5 = 0
C: IR5 + IR4 - I2 = 0

Now to rewrite those so that I can get a system of 3 equations where I need to solve for UA, UB and UC.

A: I1 + (U+UB-UA)/R2 - UA/R1 - (UB-UA)/R3 = 0
B: (UB-UA)/R3 + I2 - (UB-UC)/R5 = 0
C: (UB-UC)/R5 + UC/R4 - I2 = 0

So that would be it for the start I guess. Let me know what do you guys think, if I got the currents going in and out right and all.

I am especially hesitant about IR2 = (U+UB-UA)/R2 IR3 = (UB-UA)/R3 and IR5 = (UB-UC)/R5.

Most about the IR2.

I need to make sure I do this step correctly before I move on to solving the system of equations.

 

[gneill]

The notations on the voltage source are confusing. There's both an arrow and a "+ -" indication, and they are showing opposite polarities. Which one are we to believe?

 

[donpacino]

if you're going to do node analysis, you need to define the direction of all currents, always do 'current in', or always do current out.
that being said your equations look correct.