The Ri charging process - a stroke of genius from Fronius
The effective inner resistance of the battery "Ri" is a battery-specific value that changes during charging and discharging due to fluctuating acid concentrations and parasitic effects, such as diffusion processes, polarisation-overvoltage or the conversion of lead sulphate into lead oxide. The really special feature of the unique Ri characteristic is that the charging voltage is determined by measuring the effective inner resistance. This ensures that the charging current adapts automatically to remain in line with the effective inner resistance curve of the battery. Hence, if the effective inner resistance rises such that the current-input capability of the battery is lower than when charging began, then the charging current will be lower and charge losses avoided. Should the effective inner resistance drop during charging (current-input capability increases), the charging current is increased automatically so that it can be reduced later during the charging process, again as a function of the increasing effective inner resistance, since the battery will now be fully charged and its current-input capability correspondingly lower. This means that every charging cycle for every battery is a one-off with its own individual characteristic.

To enable the battery charging system to specify the starting value and the ongoing progression of the charging voltage, the current battery state of charge is continually recorded. During this process, the type of battery in question, how old it is, its temperature and discharge level are all monitored. The battery charging system software then uses this battery information to modify the individual charging phases by keeping the voltage curve constant and regulating the charging current in line with the effective inner resistance curve. The Ri charging process from Fronius is therefore a self-regulating process - a true stroke of genius. The charge losses at the start of charging shrink to a minimum due to the lower power requirement. The consequences: a saving in energy and only insignificant warming of the battery. There is hardly any overcharging at the end of charging, as the current drops.

Thanks to the individual Ri charging characteristic, the newly developed "Selectiva" devices achieve charging efficiency levels that were previously inconceivable: a staggering 90 percent. Combining this with device efficiency, which Fronius has been able to increase to 93 percent by commercially acceptable means, results in a total efficiency value of 84 percent - a figure that has never been attained before.

Particularly energy efficient is the fact that one only has to specify the battery voltage and the charging time, as in reality many batteries that are connected to the battery charging system tend to be only partially discharged. By specifying a charging time, however, the charging process can be extended over the whole period. This enables the battery to be charged very gently due to the lower energy input and the correspondingly lower warming effect. For companies with fluctuating forklift truck utilisation levels, harmful overcharging is prevented and the precious batteries remain undamaged. Furthermore, peak currents are prevented in situations where the charging of a number of forklift truck batteries starts simultaneously at the end of a shift. Peak currents are to be avoided, as they drive up costs.

Enhancements that shift the limits
Achieving maximum battery service life is only one of the many features that make the new generation of Ri characteristic devices from Fronius so attractive. The new devices boast many other enhancements that supplement the outstanding features already present in the existing "Selectiva" range. A few key facts: the largest variant (80 V with 180 A) now weighs only 30 kg instead of 40 kg and is smaller in size. The ventilation system has also been reworked. It now reduces contamination inside the battery charging system even further. The focus for the Fronius developers was to significantly improve safety, user-friendliness, service and system monitoring. Our highly trained employees in the Fronius Sales and Service network will be able to tell you about other energy-saving and trail-blazing features of the "Selectiva" series with the Ri characteristic.