Nodal Analysis: Understanding Method & Solving for Unknown Voltage

[influx]

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?

 

[donpacino]

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?

 

[influx]

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.