I am trying to determine the mesh currents in the following circuit. I consider the mesh currents (from left mesh to right mesh) to be called I1 and I2.


simulate this circuit – Schematic created using CircuitLab

Considering the two meshes present in the circuit, I obtain the following system of equations:

Mesh 1

(400k)I1 - (180k)I2 = -24

Mesh 2

(-180k)I1 + (457k)I2 = 27.3

Solving the above system of equations on my own yields the results:

I1 = 40.25uA and I2 = -43.88uA

I've double checked and everything seems okay in terms of mesh equation setup. Then I've verified my results with a simultaneous equation solver. However, I've simulated this circuit and the results of my simulation do not agree with the system of equations... Here are the results of my simulation, what is going on?

Simulation Results

In case you cannot see the image, the results of the simulation are...

I1 = 57.82uA and I2 = 36.96uA

  • 2
    \$\begingroup\$ Depending how you define your meshes, the current through the 180k resistor should be either I1 + I2 or I1 - I2, not just I1 or just I2. \$\endgroup\$
    – The Photon
    Dec 1 '17 at 22:59
  • 3
    \$\begingroup\$ Or if you already did that but combined terms in a way that confused me, consider that 180 + 120 is not 400. \$\endgroup\$
    – The Photon
    Dec 1 '17 at 23:01
  • \$\begingroup\$ @ThePhoton Ugh... You are right. \$\endgroup\$
    – Snoop
    Dec 1 '17 at 23:01
  • \$\begingroup\$ @ThePhoton I actually went through simulating this and calculating it out multiple times by hand and using a systems of equations solver and missed that every single time. \$\endgroup\$
    – Snoop
    Dec 1 '17 at 23:02

180 plus 120 is not 400, that's the problem.

  • \$\begingroup\$ 2+2 = 4-1 = 3, quick mafs. \$\endgroup\$ Dec 1 '17 at 23:30

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