# Mesh analysis help

1. Apr 17, 2010

### James889

Hi,

I have the following circuit:
[PLAIN]http://img265.imageshack.us/img265/6476/upg2.png [Broken]

But when i try to calculate the mesh currents i end up with the wrong answer.

This is what i did:
Equation for i1:
$$6i_1 + 18(i_1-i_2) -30$$
Equation for i2:
$$17i_2 + 18(i_2-i_1) -19$$

Adding currents in the first equation:
$$24i_1 - 18i_2 -30$$

Adding currents in the second equation:
$$35i_2 - 18i_1 -19$$

$$18i_1 = 35i_2 -19$$
$$i_1 = 1.94i_2-1.056$$

Inserting into the first equation i get
$$24(1.94i_2-1.056) - 18i_2 -30$$

Which gives that $$i_2 = 1.93$$ but that's wrong

Where did i go wrong ?

/james

Last edited by a moderator: May 4, 2017
2. Apr 17, 2010

### ejk5401

you need to get a determinant for the matrix first notice its a 2 x 2 so you would put it in like this rt in first minus the r they share and the same for the second, then you'd use the voltage on the side [24 -18]30
[-18 35] 19
then you sub in the 30 and the 19 for a then b once you have that its a/d and b/d

Last edited by a moderator: May 4, 2017
3. Apr 17, 2010

### The Electrician

Why do you think your answer is wrong? Is it because the answer given by the text book (or your instructor) is different? Sometimes text books have the wrong answer for problems.

I1 = 2.69767
I2 = 1.93023

4. Apr 17, 2010

### James889

Alright thanks, looks like the answer in my textbook is wrong.

5. Apr 17, 2010

### SpartanG345

just wondering what text are u using?

6. Apr 19, 2010

### ammontgo

2 Equations & 2 Unknowns.
My Equations

Mesh 1:
[PLAIN]https://dl.dropbox.com/u/4645835/MATH/mesh1.gif [Broken]

Mesh 2:
[PLAIN]https://dl.dropbox.com/u/4645835/MATH/mesh2.gif [Broken]

Last edited by a moderator: May 4, 2017
7. Apr 21, 2010

### ejk5401

I never said you were wrong, I shown him how to apply mesh anly so he could use it in the future. if you notice i didn't give an answer ;)