Thevenin's law - tricky example.

[piotrekn95]

Hello everyone,

I've been trying to solve this circuit. I have to use Thevenin's method to find the I5 current - so I tried to calculate the Thevenin's voltage and Thevenin resistance.

I tried to change the triangle settings of resistors to star, but I don't know if it will help. Do you have any pieces of advice on how to start solving it?

[ads-ee]

Why is there a current source shown but a voltage is given as if it was supposed to be a voltage source?

[piotrekn95]

It's just the symbol which are used at my university to draw a "voltage source".

[ads-ee]

It's just the symbol which are used at my university to draw a "voltage source".

Well it's the wrong symbol...says a lot about your university.

[CataM]

1) Change R1,R2,R3 to star. Leave the other triangle as is because you will lose track of I5 otherwise.
2) Then, you will have another triangle formed by R7, R6 and 2 other resistors that come from the star you just formed. Change again to star.
3) You are left with simple parallel/series connections. You are done.

[andre_teprom]

It's just the symbol which are used at my university to draw a "voltage source".

It is indeed a current source, having an unknown current (to be calculated), but with a given voltage across its terminals for the above equivalent thevenin load.

[piotrekn95]

What do you think about that? Could it be correct? Of course Ra, Rb, Rc will be calculated from triangle/star formulas.

[CataM]

Yes, looks good.

[andre_teprom]

Each one has their own standpoints and all of them would give the same result; I would particularly prefer to perform the Δ-Y conversion in both sets R1/R2/R3 and with R4/R5/R6. At the end you will have two arms of series resistors in parallel, with two others in series, namelly:

REQ = { R2Y + [ ( R3Y + R7 + R4Y ) || ( R1Y + R5Y ) ] + R6Y }

[piotrekn95]

Ok, I know what i should do with resistors. But now, for example I want to calculate the Thevenin's voltage on A B terminals. Is it possible to use the node potential method ?
It will be a problem that I have lonely voltage source in the branch ?

Regards

[CataM]

No, just calculate the voltage between A-B with whatever method you want.

You can see that you have another triangle there. It might be easier to convert it to star.