# Help with KVL/Supernode analysis problem

#### drcne

Joined Aug 3, 2017
15

https://imgur.com/a/VW2qM

I really can't understand why Loop 1 is + - - +, and why the current is CW not CCW. I've been staring at this for 30 mins and I can't figure it out so any help would be greatly appreciated.

Also, how do I embed a imgur picture? It never works for me.

#### JoeJester

Joined Apr 26, 2005
4,390

#### WBahn

Joined Mar 31, 2012
26,398

https://imgur.com/a/VW2qM

I really can't understand why Loop 1 is + - - +, and why the current is CW not CCW. I've been staring at this for 30 mins and I can't figure it out so any help would be greatly appreciated.

Also, how do I embed a imgur picture? It never works for me.
It would really help if you provided the schematic for the problem. As it is, we have to try to reconstruct it from modified versions of it. Please don't make us guess.

Don't try to embed images from 3rd party sites. Instead, upload the image files to the post (use the "Upload a File" button) and embed them from there. That way they are archived along with the post on AAC's server.

You can run your loops either way. You can even flip a coin for each one. Then you can flip a coin to determine if you are going to sum up the voltage drops or the voltage gains as you go around the loop. Totally up to you. You just need to make sure that each equation is consistent with your choices.

I don't know what you mean by Loop 1 being +--+.

As near as I can tell they are using the Loop 1 and Loop 2 to establish the constraint equations between the nodes internal to the two supernodes.

#### drcne

Joined Aug 3, 2017
15
It would really help if you provided the schematic for the problem. As it is, we have to try to reconstruct it from modified versions of it. Please don't make us guess.

Don't try to embed images from 3rd party sites. Instead, upload the image files to the post (use the "Upload a File" button) and embed them from there. That way they are archived along with the post on AAC's server.

You can run your loops either way. You can even flip a coin for each one. Then you can flip a coin to determine if you are going to sum up the voltage drops or the voltage gains as you go around the loop. Totally up to you. You just need to make sure that each equation is consistent with your choices.

I don't know what you mean by Loop 1 being +--+.

As near as I can tell they are using the Loop 1 and Loop 2 to establish the constraint equations between the nodes internal to the two supernodes.
When I say +- -+, I'm talking about how they labeled the voltages in loop 1. The way it is now, it looks like current flows from high voltage to low voltage(+ > -), and then from a low voltage to a high voltage (- > +). I don't understand why it is labeled this way.

And sorry about that, I'll upload another picture of the original diagram.

#### WBahn

Joined Mar 31, 2012
26,398
As with the direction of the current loops, you can flip a coin when you assign the polarities of voltages. You just need to be consistent.

In this case, they are merely explicitly showing the definition of the four node voltages. For instance, v1 is, by definition, the voltage at the top left node relative to the reference node, which is the bottom node. The same for the other three.