# Is there current flowing though a power source?

Would there be any current flowing though an ideal voltage source? I am asking this more specifically when you are analyzing a circuit and you are doing nodal analysis. I know i=v/r, but since the source is ideal, resistance would be zero or infinity?

Would there be any current flowing though an ideal voltage source?

Yes. An ideal voltage source will produce whatever current is needed to maintain its voltage. This current will flow in a complete circuit through the source and through whatever network is connected to the source.

I am asking this more specifically when you are analyzing a circuit and you are doing nodal analysis.

The nodal analysis cannot be done on a circuit that contains a voltage source. There is a variant called the modified nodal analysis that must be used instead.

I know i=v/r, but since the source is ideal, resistance would be zero or infinity?

I = V/R is the characteristic equation for a (linear) resistor. This equation doesn't apply to a voltage source or to any othe circuit element besides a resistor.

The equation for a voltage source is simply V2 - V1 = V, where V2 and V1 are the (appropriately labeled) voltages of the nodes connected to the source and V is the voltage generated by the source.

The internal resistance is 0. An ideal voltage source is there in order to supply current at a constant voltage. The amount of current flowing through it is entirely determined by the outside circuit. Imagine a short circuit with an ideal voltage source. The current would skyrocket to infinity (Obviously any real voltage source would soon run out of generation capacity to supply the circuit.) This is why voltage sources and current sources are sometimes said to be opposites or "duals" of each other. An ideal current source supplys no power to a short circuit.

Wikipedia provides a good explanation of this. http://en.wikipedia.org/wiki/Voltage_source

• i think you meant to say "An ideal current source supply no current to an open circuit." Commented Feb 21, 2014 at 17:57
• I meant to say it supplies no power because the voltage is 0 so P = I*V = 0. Thanks. Commented Feb 21, 2014 at 18:04
• I'm uncomfortable with a voltage source running out of charge since they don't store charge.
– BMS
Commented Feb 21, 2014 at 23:31
• @BMS Good point. I suppose that I was thinking too specifically of a battery. Do you know of a better term for the limitations on real world devices such as batteries, generators etc. Generation capacity? No real world source can keep up a constant voltage in a short circuit. Commented Feb 22, 2014 at 0:38