Reverse current (chargers)
In the case of electric chargers, reverse current is the current that flows back from a charged accumulator into the previously feeding circuit as soon as the charging process is interrupted or ended. The battery gives off power, which is usually undesirable because it is provided as an energy source in a working circuit. The reverse current reduces the stored electrical energy , the battery charge becomes weaker, and if the reverse current continues, the battery can be completely discharged.
Mains operated chargers
Some charger manufacturers describe reverse current as the current that the charger consumes from the battery when the power plug is not connected. This current can range from less than 1 mA to significantly higher values.
A reverse current of 1.3 mA, for example, corresponds to a capacity loss of 1 Ah / month if the device is connected to the battery but not to the mains. With a 12 volt battery that would be an energy loss of 12 Wh per month.
alternator
Up to the 1970s, alternators in vehicles were designed as direct current generators . With these, a reverse current can flow back from the vehicle battery via the alternator if the voltage of the alternator falls below that of the vehicle battery due to falling speed , and the battery discharges in a short time. That is why switches (reverse current switches ) are built into the alternator circuits , which are opened when reverse current occurs.
With the availability of high-performance rectifier diodes, three-phase generators have established themselves as alternators since the 1970s . The diodes also prevent reverse current from flowing.
Photovoltaics and solar technology
Solar modules as a source of energy
In photovoltaics and solar technology , the solar cells act as a source of power in a similar way to the chargers or alternators described above, except that they do not convert the energy from the socket or from rotating generators , but from solar energy. If their voltage falls below that of the supplied network , there would be reverse current from the network into the modules. Since this is absolutely undesirable (destruction of the solar cells), suitable switches are also provided here, which immediately disconnect them from the mains if the module voltage drops.
Reverse current between modules
Often several modules should be connected in parallel in order to be able to draw more current from the system. In the case of a parallel connection , the same voltage is applied to both modules - assuming the same type - and the partial currents add up as long as both modules are irradiated by the sun in the same way. In the case of uneven solar radiation, for example when a module is in the shade, different voltages occur on the two modules, which then lead to a reverse current through the shaded module. The question of whether this reverse current is harmful to one or the other module is currently answered differently. In the interest of a high degree of efficiency of the entire system, currents between the modules that do not emit energy into the network to be fed should be avoided.