# How to find equivalent circuits

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1. Mar 26, 2016

### Puglife

Hi, I need to learn how to find equivalent circuits using what my textbook calls open circuit and short circuit methods.

Thank you all for you support

2. Mar 26, 2016

### phinds

Then I suggest you study your text book and learn exactly that. If you have specific questions, then ask.

3. Mar 26, 2016

### Puglife

That wasn't that helpful of an answer, their is a reason I am asking a physics forum on electrical engineering instead of either googling it or using what little my textbook had on it. If you want a more direct question it is this, how do you set up, and solve a equivalent circuit using an open and closed circuit model?

4. Mar 26, 2016

### phinds

Draw any particular circuit for which you would like such a solution and then attempt to solve it and then if/when you get stuck post the circuit and what you have tried so far.

5. Mar 26, 2016

### Puglife

All I know how to do for equivalent circuits is how to use the parallel and series resistive equations, that does to my understanding get the equivalent circuit, what I want to know, is how to even begin doing it with the short and open circuit methods, and now, why would I use those methods over just series and parallel resistor rules.

Thanks, your response time is amazing

6. Mar 26, 2016

### phinds

I want to help you on this but I'm just not clear what you are asking. What is your understanding of, say "the open circuit method" and how it is different from just doing computing the equivalent resistances?

7. Mar 26, 2016

### Puglife

i do not know the difference between the two, or really what the open circuit method is. I know how to find equivalent resistance using parallel and series equations, but my textbook keeps refering to a open circuit method that they did not talk about. I dont know how to even start doing it, or what it really is.

8. Mar 26, 2016

### phinds

Can you scan a paragraph out of the book where they are discussing it?

9. Mar 26, 2016

### Puglife

unfortunately, I do not own a scanner, or a camera, so that would be kind of difficult. I am living on an extremely low budget right now. but is their a method for solving the thevanine equivalent circuits using open or closed circuits?

10. Mar 26, 2016

### mathwhiz

It's helpful to find equivalent circuits because you can narrow a circuit with many resistors and a source to just one source and one resistor. The only thing you are doing with open circuit is removing the load resistor, for circuits 1 it's typically the resistor on the far right, or on the other side of the source.After removing the load you look into the circuit from that end and perform all your parallel and series transformations until you get down to one equivalent resistor and the source. The benefit being now you can quickly find current and other information for different loads. The problem is you lose any information if needed about individual resistors. It has been a while so I need to look again at why you use short circuit method, I know you are replacing the load resistor with a current source, typically 1 amp and use it to find something.

11. Mar 26, 2016

### Puglife

Is their any way you can supply sample equations for short circuit and open circuit methods, I am just starting out, and It would really be helpful to me.

Thank you guys so much for all of your help

12. Mar 26, 2016

### phinds

Just google "Thevenin equivalent circuit" and "Norton equivalent circuit". There are plenty of explanations and examples on the internet.

13. Mar 27, 2016

### Guidestone

I think what Puglife is referring to is the source superposition method or the circuit superposition theorem. I had that topic during the electrical circuits analysis a year ago so I can't recall much
(shame on me). What I remember is that in order to obtain an equivalent circuit, voltage sources are replaced with open circuits and current sources are replaced with short circuits.

14. Mar 27, 2016

### Guidestone

Norton and Thèvenin theorems came up later in the course and they both have similarity with the superposition method.
I've read another post of yours and my guess is that your book is not really helpful. Try introduction to circuit analysis from Boylestad and Nashelsky. This book covers both voltage dividers and equivalent circuit theorems.
Good luck bro.