Short Circuit Current Calculation

In summary, the conversation is about finding the short circuit current for a circuit with a Thevenin equivalent resistance. The speaker is trying to simplify the circuit using KVL and substitute variables to get rid of v2 and v3. They are also discussing the relationships between v1, v2, and v3. Eventually, they are able to solve for v3 and determine that v2 = v1.
  • #1
magnifik
360
0
i am trying to find the short circuit current for the following circuit.
23r4axx.png

the RL is the thevenin equivalent resistance. i am trying to find the current when RL is a wire (short circuit).

by KVL, i have
IR1 + [tex]\mu[/tex]1(v2-v1) + IR2 + [tex]\mu[/tex]2(v3-v1) + IR3 = 0

(the above is not formatted correctly. it should be
IR1 + m1(v2-v1) + IR2 + m2(v3-v1) + IR3 = 0 )

what i am having trouble with is trying to simplify it. specifically, i am trying to get rid of v2 and v3

can i substitute v3 = IR2
and v2 = IR1
??

thanks.
 
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  • #2
magnifik said:
i am trying to find the short circuit current for the following circuit.
the RL is the thevenin equivalent resistance. i am trying to find the current when RL is a wire (short circuit).

Assuming you are placing your ground at the bottom of the circuit, what can be said about v1 and v2?

If you want to simplify it more, express v1 and v3 in terms of the current times their respective resistance(s).

(HINT: Maybe there is a reason I didn't explicity tell you to solve for v2)
 
  • #3
jegues said:
Assuming you are placing your ground at the bottom of the circuit, what can be said about v1 and v2?

If you want to simplify it more, express v1 and v3 in terms of the current times their respective resistance(s).

(HINT: Maybe there is a reason I didn't explicity tell you to solve for v2)

Are the following relationships correct...
v1 = IR1
v2 = v1
v3 = IR2
 
  • #4
magnifik said:
Are the following relationships correct...
v1 = IR1
v2 = v1
v3 = IR2

Give v3 another shot!

Remember it's not simply the voltage across that one resistor, it's the voltage at that node with respect to ground.
 
  • #5
jegues said:
Give v3 another shot!

Remember it's not simply the voltage across that one resistor, it's the voltage at that node with respect to ground.

is it correct to solve it in this way
v3 + m1(v2-v1) / R2 = 0
v3 = -m1(v2-v1)
 
  • #6
You told me in your above post that v1=v2, so your implying that v3=0?

V3 isn't 0.
 
  • #7
i got v3 = -m1(v2-v1), not 0
 
  • #8
You told me v2=v1, thus v2-v1=0.

Which is in your expression for v3, is it not?
 
  • #9
oh, i see now. I'm still having trouble trying to figure out v3.
 
  • #10
i tried to do source transforms and analyze viz node method and got
v3 = -v1m2R2/(R3 - m2R2)
 
  • #11
magnifik said:
i tried to do source transforms and analyze viz node method and got
v3 = -v1m2R2/(R3 - m2R2)

Okay now that we know that the voltage source is effectively 0 volts wouldn't v3 be defined as follows,

V3 = I(R1 + R2) ?
 
  • #12
ahh yes, i see that. thanks. were my other assumptions correct?
v1 = v2 ?
 
  • #13
magnifik said:
ahh yes, i see that. thanks. were my other assumptions correct?
v1 = v2 ?

I'm not trying to be rude, but have you read my replies?

I had told that v2-v1 = 0.

So yes, v2 = v1.
 

Related to Short Circuit Current Calculation

1. What is Thevenin equivalent current?

Thevenin equivalent current is a simplified model used to represent a complex network of resistors and voltage sources. It is the current that would flow through a load if it was connected to a Thevenin equivalent circuit.

2. How is Thevenin equivalent current calculated?

The Thevenin equivalent current is calculated by finding the open circuit voltage of the circuit, also known as the Thevenin voltage, and dividing it by the total resistance of the circuit.

3. Why is Thevenin equivalent current useful?

The Thevenin equivalent current is useful because it allows us to simplify a complex circuit into a single voltage source and a single resistor, making it easier to analyze and understand the behavior of the circuit.

4. What are the assumptions made when using Thevenin equivalent current?

The assumptions made when using Thevenin equivalent current are that the circuit is linear, meaning the current-voltage relationship follows Ohm's law, and that the load is resistive, meaning it does not contain any capacitors or inductors.

5. How accurate is Thevenin equivalent current?

The accuracy of Thevenin equivalent current depends on the accuracy of the assumptions made. If the circuit is not linear or the load contains capacitors or inductors, the Thevenin equivalent current may not be an accurate representation of the actual circuit behavior.

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