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I am struggling to find the thevenin equivalent voltage for the following circuit. I attempted using source transformation and mesh analysis by initially transforming the current sources into voltage sources, leaving me with a 6v source, 6 ohm resistor, 14V source, 14 ohm resistor, 15V source, and a 5 ohm resistor all in series.

I used mesh analysis and got that the current through the circuit was 1.4A. I multiplied this value by the 5 ohm resistor, and got 7V, however, the answer is 8V. What did I do wrong, and how can I solve this?

toolic
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Jason2134
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1 Answers1

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Here's a hint or two. Transform the sources and redraw like this: -

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Can you take it from here?

Relative to node (b) -8 volts is the right answer for node (a): -

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And clearly the voltage on node (a) relative to node (b) is -8 volts.

Andy aka
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  • Hi, thanks for the help. I tried this similarly before and ended up source transforming the current source and adding it up with the 20V source and adding the resistances. I got a simple circuit with a single 35V source and 25 ohm resistor. I have no idea where to go from there, and I have no idea how else to solve it from there. What should I do? – Jason2134 Mar 08 '23 at 11:26
  • @Jason2134 transform the 20 volt source and 20 ohm resistor back to a current source in parallel with a resistor is the next step. Then merge the resulting parallel current sources into a single current source (noting polarities) and, likewise, the two resulting parallel resistors can become one and, you are left with a current source in parallel with a resistor. You should work at this. – Andy aka Mar 08 '23 at 11:30
  • Thanks a lot, that did work out. Just to confirm, I got a -2A current source in parallel with a 4 ohm resistor, which then outputs the -2*4=-8V thevenin voltage, which is what I should have gotten right? Also, how come my initial method of mesh analysis not working? Thanks again for the help, very useful. – Jason2134 Mar 08 '23 at 11:48
  • Yes, it was your final step that was faulty. When you calculated 7 volts, that is only across the 5 ohm resistor but, between node (a) and node (b) is a 5 ohm resistor in series with a -15 volt source so, +7 added to -15 = -8 QED. @Jason2134 – Andy aka Mar 08 '23 at 11:59