• Support PF! Buy your school textbooks, materials and every day products Here!

Circuits Question: Thevenin Equivalent

  • Engineering
  • Thread starter Ready2GoXtr
  • Start date
  • #1

Homework Statement



Find thevenin equivelent of this circuit with respect to a and b

part0.jpg


Homework Equations


Mesh Currents

The Attempt at a Solution


Here I will try to find V(open circuit) = Vth = Vab ((I think this anyways))

I apply mesh currents (any faster methods are welcome if you know them)
part1.jpg


iA: -100/V/ + 10/ohm/(iA) + 40/ohm/(iA-iB)=0
iB: 40/ohm/(iB-iA) + 50/ohm/(iB-iC)=0
iC: 50/ohm/(iC-iB) + 20/ohm/(iC) + 200/ohm/(Ix) = 0
iD:-10/A/
iX: iX=iB-Ic

I get the folowing values using solve function on calculator:
iX=-40A/
iA=210/A/
iB=260/A/
iC=300/A/
iD=-10/A/

And using ohms law with parallel resistors having equal voltages..
Vab = 40/ohm/*(iA-iB) = -2000 = Voc = Vth

Now is where I begin to have trouble finding Isc...


I draw the short circuit between a and b (which I believe causes R3 and R4 to have no current through them thus making Ix = 0 and vs2 = 0 as well):

part2.jpg


Simplifying it you gain ((if my previous assumptions are correct reguarding the short circuit)):

part3.jpg



Now from here I am actually unsure what I should do. I do want to do mesh currents but I dont know if I will recieve a correct answer. I also wondered if I could use a closed surface... something like this perhaps:

part4.jpg


If I used that I would get an equation like -100/V/ / 10/Ohms/ + Isc = 0

But then again it just doesnt seem quiet right to me. And i have no way to check my answer.
 

Answers and Replies

  • #2
The Electrician
Gold Member
1,249
155
You could get rid of the 10 amp source (Is) right from the beginning; it does nothing to the circuit to the left of Vs2. It just adds 10 amps to the current in Vs2, which has no effect on Vs2's voltage.

So, Is contributes nothing to the current in the short you've placed across a-b because Vs2 absorbs the entire 10 amps from Is, and the current in the a-b short is just 10 amps.
 

Related Threads on Circuits Question: Thevenin Equivalent

Replies
12
Views
839
Replies
5
Views
1K
Replies
4
Views
3K
Replies
8
Views
3K
Replies
4
Views
570
Replies
4
Views
2K
Replies
22
Views
2K
Replies
1
Views
1K
Replies
5
Views
799
Replies
2
Views
1K
Top