Float Charge - SMA SUNNY ISLAND 8.0H Installation Manual

9 Battery Management
The first value reached limits the charge current of the battery. While the charge current remains
constant, the battery voltage increases with increasing state of charge. The constant current phase
ends when the cell voltage of the battery reaches the target value specified for the relevant battery
type.
Constant Voltage Phase
In the constant voltage phase, battery management attempts to charge the battery fully. In this phase,
the battery voltage remains constant while the battery current slowly reduces. For the constant voltage
phase, battery management chooses one of the following three charging processes:
• Boost charge
• Full charge
• Equalisation charge
The off-grid inverter has a specified time for each charging process: Once this time has elapsed, the
constant voltage phase ends. The off-grid inverter switches to float charge.

Float Charge

The purpose of float charge is to maintain the battery in a fully charged state without overloading the
battery. At the beginning of float charge, battery management reduces the charging voltage in steps
until the target value specified for float charge has been achieved. 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 rated 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
energy-saving mode.
Energy-Saving Mode
In energy-saving mode, the off-grid inverter switches to standby, thus saving energy.
If a set time for float charging has elapsed for grid backup systems, battery management switches to
energy-saving mode and the stand-alone grid is supplied only by the electricity grid and the AC
sources in the stand-alone grid. The off-grid inverter exits energy-saving mode at configurable time
intervals or when the battery voltage per cell drops by 0.14 V (see Section 7.22 "Setting the Silent
Mode", page 113). In this way, the battery always remains fully charged. If the electricity grid fails
in energy-saving mode, the off-grid inverter provides a stand-alone grid within seconds.
126 SI80H-60H-OffGrid-IA-en-11
SMA Solar Technology AG
Installation Manual