Proper charging is one of the most important factors to consider when using maintenance-free sealed
lead acid batteries. Battery performance and service life will be directly affected by the efficiency of the charger selected. Charging methods are dependent on battery applications like main power application and standby / backup power application.
Main power application (Cycle use):
a) Standard charging (Constant Voltage charging)
b) Rapid charging
Standby / backup power application ( Float use):
a) Float charging
In continuation from last week, today we are going to discuss about the Standby / backup power application (Float use).
Standby / Backup use (Trickle use)
The application load is supplied with AC power in normal state. Standby / Backup use are to maintain the battery system at all times so that it can supply power to the load in case the AC input is disrupted (such as a power failure).
Float charge
The purpose of float charge is to maintain the battery in a fully charged state without overcharging it. At the beginning of float charge, battery management reduces the charging voltage in steps until the set point specified for float charge has been reached. Battery management then maintains this charging voltage until the end of float charge. Float charge ends when one of the following conditions is met:
• The total of all electric discharges of the battery has reached 30% of the nominal capacity.
• The current state of charge is less than 70% of the available charging capacity.
Battery management switches from float charge to the constant current phase. If the stand-alone grid is connected to the electricity grid, battery management can also switch from float charge to silent mode.
The float charge voltage should be set as follows. Hereby, the Volts per cell multiplied by the number of cells must be measured at the end terminals of the battery:
2.27 Vpc (at 25 °C)
All charging (float, boost, equalizing) must be carried out according to an IU-characteristic with limit values: I-phase: ± 2%; U-phase: ± 1%.
These limits are acc. to the standard DIN 41773, part 1 [5]. The charge voltage shall be set or corrected, respectively, to the values mentioned above.
