SMA SI 3324 - Manual (Page 38)

Battery Management SMA Technologie AG
Page 38 SI3324/4248-14:FE2406 User Manual
For this reason, the Sunny Island 3324/4248 automatically performs regular
equalization charging every 60 days or after every 30 charging throughputs. The
equalization charging uses controlled overcharging of the battery bank to ensure
that even the weak cells are fully charged. Equalization charging leads to a further
significant increase of battery service life by a factor of up to 50 %.
The charging capability of lead acid batteries is heavily dependent on the battery
temperature. For temperatures below 20°C the charging voltage must be slightly
increased, and for temperatures above 20°C it must be slightly reduced. This is
necessary to avoid overcharging and insufficient charging at all battery
temperatures. For this reason, the Sunny Island 3324/4248 is equipped with
automatic temperature compensation of the charging voltage. At temperatures
below 20°C, the charging voltage is raised by 4 mV/°C and cell (96 mV/°C for a
48 V battery) and reduced by the same amount at temperatures above 20°C. The
maximum permissible battery temperature is also monitored and the system switches
off with a fault if the limit is exceeded ("23-18 TBatMax" parameter).
6.2 Silent Mode
When operating with the public grid, in addition to the float charge a silent mode
exists. The main purpose of the silent mode is to save energy in backup systems,
where the Sunny Island 3324/4248 spends most of the time in the float charge mode
by switching from charging mode to silent mode.
Silent mode is automatically activated when the float charge charging power drawn
from the grid and flowing into the batteries is less than 40 W. In this case, one can
assume that the batteries are 100 % charged and that further charging is not
required in the next few hours.
The float charging is automatically reactivated either after twelve hours or when the
battery voltage sinks below 50.2 V. This ensures that the batteries are always fully
charged, even in silent mode. If a power failure occurs during silent mode, the Sunny
Island 3324/4248 switches to invert mode within a few milliseconds. The loads are
supplied almost without interruption.