# Need help with supernode equation

1. Oct 25, 2009

### noname1

I am trying to resolve this super node but i am having trouble with the equation, more specifically node c, this is where i got so far

5 = Va/20 +(Va - Vd)/10 + (Vb - Vc)/12.5
-10 = (Vd - Va)/10 + Vd/25
-Va + Vb = 100

please explain the c node equation

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2. Oct 26, 2009

### The Electrician

Assuming the positive end of the 150 volt battery is connected to node C, then the equation is simply: Vc = 150

3. Oct 26, 2009

### noname1

but dont we have to include the 12.5 resistor from node b to node c?

4. Oct 26, 2009

### The Electrician

That resistor is taken care of by your first equation.

When you have a voltage source connected from ground to some node, you need a (constraint) equation that simply says that the voltage at (in this case) node C is 150 volts.

It's similar to your third equation.

5. Oct 28, 2009

### noname1

i am getting an error on node d can anyone tell me what i am doing wrong, its the 3rd equation on the last process

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6. Oct 29, 2009

### The Electrician

I think that equation should be:

-5Va + 7Vd = -500