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# Thevenins and nortons circuit help

#### lp2014needhelp

Dec 18, 2014
11
Hi i'm currently struggling to convert a basic circuit to find thevenins and nortons equivalent circuit (and valves), can anyone on here help please?

R4 is the load resistor which I know I have to remove but its just working out the rest of the circuit.

Any help would be very grateful.

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#### Arouse1973

Dec 18, 2013
5,178
So for Norton's what do you have to replace R4 with? Clue it's not an open circuit. For Thevenins what do you think you have to do with R4 replace it with?. Clue it's not short circuit. And what voltage do you think you need to replace the 12 Volt with to work out the resistances? So your looking for open circuit voltage for one and short circuit current for the other. Can you work it out now?

#### lp2014needhelp

Dec 18, 2014
11
Thanks for the reply adam, Starting with Thevenins I need to remove R4 and remove the also the supply voltage the issue I have is how do I work out the resistors. I think if I put the resistor all the resistors in series then the calculation would become pretty simple.

#### Arouse1973

Dec 18, 2013
5,178
Ah this is where it can get tricky. Have you covered parallel resistors yet. I would have thought you had by the time you got to this sort of question because you are going to need it.

#### lp2014needhelp

Dec 18, 2014
11
Yes and no tbh. The issue I have is how the circuit is drawn, I don't know whats in parallel and what isn't . How do you suggest you redraw it

#### Arouse1973

Dec 18, 2013
5,178
If I redraw it for you can you now see which ones are in series and parallel? And what do you do to the voltage source?

Last edited:

#### lp2014needhelp

Dec 18, 2014
11
Yeah so I remove R4 now and that leaves R2 and R5 in parallel then = R1 +(R2+R5)+R3 to work out circuit resistance. I think??

#### Arouse1973

Dec 18, 2013
5,178
I changed the picture to match your references. So R2 is in parallel with two others that are in series, which are?

#### Arouse1973

Dec 18, 2013
5,178
Yeah so I remove R4 now and that leaves R2 and R5 in parallel then = R1 +(R2+R5)+R3 to work out circuit resistance. I think??

Remember you also have to work out the open circuit voltage don't you.

#### lp2014needhelp

Dec 18, 2014
11
which are R3 and R6.

Then R2 + (R2,R6) parallel.

then I will have 3 resistor in series

Dec 18, 2013
5,178
Yes you have it!

#### lp2014needhelp

Dec 18, 2014
11
Do you know where I can get any good examples for a circuit similar to mine? I need to tackle nortons now if your still free to help. I should be paying you by the hour LOL

#### Arouse1973

Dec 18, 2013
5,178
Here is one that works. R13 and R14 are the load.

#### lp2014needhelp

Dec 18, 2014
11
Where did you get these samples from? I would love to see the calculations to help me complete mine and check against to ensure mine is right.

Dec 18, 2013
5,178

#### lp2014needhelp

Dec 18, 2014
11
thanks adam, how good are you on nortons for the same circuit?

#### Arouse1973

Dec 18, 2013
5,178
I'll have a look later for you. I got a few things to do first. I also need to look at the way we calculate the equivalent resister. I got the answer to this but it's the series and parallel part I need to make sure I told you right.

#### Arouse1973

Dec 18, 2013
5,178
Ok I found another way to work it out for Thevenins, that I find easier. Remove the load and add a short. Work out the total resistance. Then work out the current in the circuit. Then use you Thevenins open circuit voltage to find the Thevenins resistance using this total current.

#### Arouse1973

Dec 18, 2013
5,178
Just realised, ... the output has to be open circuit to do it the original way, but even with the load removed it still has the 143K attached. So if you remove this then it works. But technically you shouldn't so I think the second way would be the best. Some of the other guys might know what to do in this case.

#### lp2014needhelp

Dec 18, 2014
11
what time will you be on adam? here's a example some of us have done today what u reckon

I think if I could work out the resistance then the rest will follow?

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