Open-circuit voltage
The open circuit voltage (german open- circuit voltage, OCV) is in electrical engineering, measured at the terminals of an open power source voltage. That is, the open circuit voltage is the voltage on the output side when no load is connected. No electric current flows, thereby no voltage drop across the internal resistance of the voltage source.
The open circuit voltage is then accurately equal to the source voltage UQ, if existing within the voltage source, like a generator or a galvanic cell, no parallel current paths, for example cause leakage currents, which reduce the open circuit voltage.
Measurement
Measuring the open circuit voltage, a voltmeter is required, which has a significantly higher internal resistance than the source. This ensures that the load on the power source by the instrument is negligible. The internal resistance current voltage measuring devices located in the megohm range, so that this condition is given in many voltage sources.
Exceptions are, for example, high-voltage sources, and in generator mode photodiodes operated in low light or photo cells - here to help electrometer or an electrometer amplifier, which - apart from the insulation resistance - have an infinite input resistance.
Examples
Transformers and Power Supplies
A transformer is in the idle when the AC voltage on the primary side and secondary side U1 is applied no load is connected. Flowing in the primary circuit, in this case, a current which is referred to as no-load current. Secondary creates the induced voltage U2 ( open circuit voltage ), which is detectable at the secondary terminals. The open circuit voltage can be twice the rated voltage ( output voltage at rated current collection ) with small transformers quite. For example, enter unregulated power supply units with less than the rated load much higher voltages than the rated voltage.
When stabilized power supplies and laboratory power supplies, the open circuit voltage, however, is not different or hardly of the rated voltage.
Accumulators and batteries
The open circuit voltage of accumulators and batteries can be used to assess their state of charge. Many automatic charger or charging circuits therefore examine when loading the open circuit voltage by periodically interrupting the charging process and measure the open circuit voltage. Depending on the result of the charging process is continued or terminated. The open-circuit voltage at end of charge is the charge voltage.
Electrical wiring
Main article line theory
A long electrical line is labeled DC voltage by the conductance per unit length of its insulation material and the resistance per unit length of the wires. Both together will cause the voltage at the end and unloaded is a little lower than the supply voltage.
Even at low frequencies, the capacitive and inductive linings of the line to take effect. The attenuation of the line increases with the frequency.
Decreases with increasing frequency, the wavelength on the line in the magnitude of the line length, other effects occur, see Lecher. Has the cable such as the length / 4, the AC voltage at the open end is towards the feeding voltage greatly exaggerated.