Open-circuit voltage


Open-circuit voltage is the difference of electrical potential between two terminals of a device when disconnected from any circuit. There is no external load connected. No external electric current flows between the terminals. Alternatively, the open-circuit voltage may be thought of as the voltage that must be applied to a solar cell or a battery to stop the current. It is sometimes given the symbol Voc. In network analysis this voltage is also known as the Thévenin voltage.
The open-circuit voltages of batteries and solar cells are often quoted under particular conditions.
The potential difference mentioned for batteries and cells is usually the open-circuit voltage. The open-circuit voltage is also known as the electromotive force, which is the maximum potential difference when there is no current and the circuit is not closed.
To calculate the open-circuit voltage, one can use a method similar to that below:
Consider the circuit:
If we want to find the open-circuit voltage across 5Ω resistor. First disconnect it from the circuit:
Find the equivalent resistance in loop 1 and hence find the current in the loop. Use Ohm’s Law to find the potential drop across the resistance C. The resistor B does not affect the open-circuit voltage. Since no current is flowing through it, there is no potential drop across it. So we can easily ignore it.
Therefore, the potential drop across the resistance C is VL.
This is just an example. Many other ways can be used.