# Thevenin Equivilant help

Discussion in 'Homework Help' started by Boboulas, Dec 12, 2010.

1. ### Boboulas Thread Starter New Member

Dec 12, 2010
5
0

Please see attached i need to work out the equivilant thevenin circuit to the left of AB

what is the process for thevenin when you have two voltages like this?

i have already worked out the resistance = 1.62Ω

any help would be appreciated

http://yfrog.com/5xtheveninj

Last edited: Dec 12, 2010
2. ### tyblu Member

Nov 29, 2010
199
16
Thevenin voltage is the open circuit output voltage, which is how it's already setup, so simply calculate the voltage from A to B. One way is to use superposition: short source #2 and calculate $V_{\small{AB,1}}$ using only source #1, then short source #1 and calculate $V_{\small{AB,2}}$ using source #2, and finally add the two together to get $V_{\small{Thevenin}} = V_{\small{AB,1}}+V_{\small{AB,2}}$.

3. ### Boboulas Thread Starter New Member

Dec 12, 2010
5
0
So therefore:
4V VAB1= 5/8*4=2.5V
6V VAB2= 5/17*6=1.764V

VT = VAB1 + VAB2
VT = 2.5V + 1.764
VT = 4.264V

Is this correct?

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
1,116
No,
For 4V Vab_2 = (3||5 ) / ( 12 + 3||5) * -4 = -0.54054054V

For 6V Vab_2 = ??

5. ### Boboulas Thread Starter New Member

Dec 12, 2010
5
0
For 6V = (12//5) / (3 + 12//5) * 6 = 3.243

therefore

3.243 + - 0.540 = 2.703 V

is this correct? am i getting any closer to grasping this?

6. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
1,116
You are very close to get the right answer.
In your diagram all voltage source have positive terminal point toward point B.
So this mean that voltage on point B has
higher potential than point A

So correct answer will be ??

Last edited: Dec 13, 2010
7. ### Boboulas Thread Starter New Member

Dec 12, 2010
5
0
im sorry im not sure, have you any more help or hints?

8. ### Boboulas Thread Starter New Member

Dec 12, 2010
5
0
does that mean it will just be a negative result?

Therefore: revised:

For 6V = (12//5) / (3 + 12//5) * -6 = -3.243

therefore

-3.243 + - 0.540 = -3.783 V

Feb 17, 2009
3,993
1,116
10. ### Jony130 AAC Fanatic!

Feb 17, 2009
3,993
1,116
Yes you right.
Vth = -3.783 V

Boboulas likes this.