Nodal Analysis: Understanding Method & Solving for Unknown Voltage

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SUMMARY

The discussion centers on the application of nodal analysis in electrical circuits, specifically addressing the calculation of unknown voltages using Kirchhoff's Current Law (KCL). The participant identifies a mistake in the initial equation used for analysis, emphasizing the importance of including all currents, particularly through the 75 V voltage source. The correct approach involves setting up KCL equations only at nodes with unknown voltages, such as Vx and V1, while recognizing that the 75 V node is fixed at 75 V above ground. The final calculated voltage Vx is determined to be 55 V, which is a critical point of confusion in the analysis.

PREREQUISITES
  • Understanding of Kirchhoff's Current Law (KCL)
  • Familiarity with nodal analysis techniques
  • Basic knowledge of electrical circuit components, including resistors and voltage sources
  • Ability to solve linear equations
NEXT STEPS
  • Study advanced nodal analysis techniques in electrical engineering textbooks
  • Practice solving circuit problems using KCL with multiple nodes
  • Explore the impact of fixed voltage sources on circuit analysis
  • Learn about circuit simulation tools like LTspice for validating nodal analysis results
USEFUL FOR

Electrical engineering students, circuit designers, and anyone involved in analyzing electrical circuits using nodal analysis techniques.

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I understand their method. However, if you use the node to the left of the 2 ohm resistor (the node where the voltage = 75 V) then you get:

(75-Vx)/2 -10 = 0

so 75-Vx = 20
so Vx - 75 = -20
Vx = 55 V

But this is not 25 V as it should be?

When doing nodal analysis, do you have to consider each node?
 
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You did not include the current through the 75 v voltage source. your first equation should have been
(75-Vx)/2 -10 -(i3+0.4*Vx)= 0

that being said when you do nodal analysis you should only do kcl's at nodes with unknown voltages. you know that the 75v node is 75 v above ground. So try a KCL at nodes Vx and V1

does that make sense?
 
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donpacino said:
You did not include the current through the 75 v voltage source. your first equation should have been
(75-Vx)/2 -10 -(i3+0.4*Vx)= 0

that being said when you do nodal analysis you should only do kcl's at nodes with unknown voltages. you know that the 75v node is 75 v above ground. So try a KCL at nodes Vx and V1

does that make sense?

Ah yes! Thanks a lot mate.
 

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