I1 - I2 = -0.4 * VaI2 - I3 = -5Mesh Method Equations for Circuit Analysis

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Discussion Overview

The discussion revolves around deriving equations for a circuit analysis problem using the mesh method. Participants explore the formulation of mesh equations, the relationships between currents and voltages, and the validity of their expressions in the context of the circuit presented.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents initial mesh equations but expresses uncertainty about their correctness and the polarities involved.
  • Another participant questions the number of equations provided, suggesting that three mesh equations should be listed instead of two.
  • A participant clarifies that the equations presented are supermesh equations due to the presence of dependent and independent current sources.
  • There is a discussion about the interpretation of terms in the equations, with participants seeking clarification on the meaning of specific coefficients and variables.
  • One participant suggests rewriting the equations to better reflect the relationships between the variables, introducing a new variable for a voltage across a current source.
  • There is acknowledgment of a potential typo in one of the equations, but overall, some participants feel the revised equations are on the right track.
  • Another participant proposes that the equations can be simplified by eliminating certain variables through subtraction, leading to new expressions for voltages and currents.
  • One participant expresses difficulty in achieving correct values for the mesh currents and seeks hints for corrections.
  • Concerns are raised about the correctness of the sign in one of the voltage equations, prompting further discussion on the direction of current flow.
  • Another participant shares their own computed values for the voltages and currents, which differ from those previously discussed, indicating uncertainty about the correctness of the equations.
  • Finally, a participant asserts a different set of equations, suggesting a potential resolution to the ongoing confusion, but it remains unclear if there is consensus on these new equations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the equations or the values derived from them. Multiple competing views and uncertainties about the equations persist throughout the discussion.

Contextual Notes

Participants express uncertainty regarding the polarities of voltages, the interpretation of terms in the equations, and the overall correctness of their derived expressions. There are unresolved questions about the relationships between the variables and the impact of the dependent current source on the equations.

esmeco
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I'm trying to get the equations for this exercise but they're giving me some troubles...I think this could also be done with node voltage,but I've tried with the mesh method.Those are my equations:

Eq.1: -13 + 4xI1 + 6xI1 + 2.5xI2 + 7.5xI2=0
Eq. 2: 2.5xI2 + 7.5xI2 + 2xI3 + 8xI3 + 0.8vo=0

Va=-2xI3
Vo= -13 + 4xI1 + 6xI1
I1- I2=-0.4va
I2-I3=-5

http://i75.photobucket.com/albums/i281/esmeco/Meshmethod.jpg

I'm not sure if those equations are right(which probably aren't because the solution doesn't match) and I'm a bit in doubt with the polarities...Any help is really appreciated!Thanks in advance...
 
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Sorry, I'm confused. There are three mesh circuits, but you only have two equations listed (with more terms each than I would expect). What are your beginning three equations?
 
Well,those are the 2 supermesh equations,since there is the dependent current source and the current source which are both shared by two mesh circuits...So,the 3 equations for the individual meshes would be:

Eq. 1:-13 + + 4xI1 + 6xI1 + Vo=0
Eq. 2: +0.4Va + 2.5xI2 + 7.5xI2 + 5=0
Eq. 3: 2xI3 + 8xI3 + 0.8Vo + 5=0
 
When you perform a mesh what values are writing down?

For example in this expression that you wrote:

Eq. 3: 2xI3 + 8xI3 + 0.8Vo + 5=0

What is [tex](2)(I_3)[/tex] ?
What is [tex](8)(I_3)[/tex] ?
What is [tex](0.8)(V_0)[/tex] ?
What is [tex]5[/tex] ?
 
Well,I'm trying to determine the mesh current using voltages,so the 2xI3 and all those values are the voltages...
 
But 0.4*Va is a current. That is a voltage dependent current source. The voltage across is is Vo.
 
So re-writing the equations they would be like this?

Eq. 1:-13 + + 4xI1 + 6xI1 + Vo=0
Eq. 2: -Vo + 2.5xI2 + 7.5xI2 -V1=0
Eq. 3: 2xI3 + 8xI3 + 0.8Vo +V1=0

V1 would be the voltage on the 5A current source...
 
I think that looks better. There's a small typo in equation 1 with a ++, but other than that I think you are on the right track.
 
So,those equations would reduce to one equation since subtracting V1 from equation 2 and equation 3 would eliminate it and would also eliminate Vo from the equations since we would subtract Vo from eq. 1 and 2...Am I right?
Also we would have equations for Vo,Va,I2-I1 and I3-I2:

Va=-2xI3
Vo=-13 + 10xI1
I2 - I1=0.4va
I3 - I2=5

I hope these are right...
 
  • #10
I've tried to use those other equations on my main equations to get the values of the currents on the meshes,but unfortunately with no success...Could anyone give me some hints on how to correct them?
 
  • #11
esmeco said:
Va=-2xI3
Vo=-13 + 10xI1
I2 - I1=0.4va
I3 - I2=5
Is the sign correct on Vo?
 
  • #12
Well, the inicial equation for Vo,I think, it would be like this:

-13 + 4xI1 + 6xI1 - Vo=0

Since the current is flowing in a clockwise direction I think it would be -Vo...Am I right?Also,are the other equations right?
 
  • #13
So, Vo woould be Vo=13 - 10xI1?It's kind of difficult for me to get Vo equation(if it wan't the one I provided)...
 
  • #14
Like your other problem with the nodal analysis, I am unsure if the given answer is correct. I got Vo = 56.863, I1 = -4.3863, I2 = -1.9314 and I3 = 3.0686 when I tried to work this one out.
 
  • #15
Well, the solutions I had for the currents aren't even close to that...ANd also,the problem is I'm not even sure if these equations are right:

Va=-2xI3
Vo=-13 + 10xI1
I2 - I1=0.4va
I3 - I2=5

Especially Vo I don't know if it's right...Any more help is greatly welcomed...
 
  • #16
I believe the correct equations are:
Va = 2 * I3
13 = 10 * I1 + Vo
 

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