SMA SI 3324 Installation - Manual (Page 105)

SMA Technologie AG Battery Management
Installation Guide SI3324/4248-14:SE2406 Page 105
11.2 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.
11.3 Deep Discharge Protection/Battery State
When deeply discharged, lead acid batteries age 100 times more quickly than when
fully charged. Depending on the battery type, one speaks of deep discharge at
charge levels of less than 40 %. Reliable protection from deep discharge is essential
for a long battery service life. Pure monitoring of the battery voltage with fixed
battery voltage limits is not really suitable for this task. Under heavy loads the system
is switched off much too early, and under light loads it is switched off much too late.
The fault rate can lie above 50 %. For this reason the Sunny Island 3324/4248 uses
current-compensated voltage thresholds combined with time delays for deep
discharge protection. The different levels, which can be easily set, are used to define
the four state of the batteries (BatState):
• Normal operation (BatState = Normal)
• 1st level (BatState = Warning)
• 2nd level (BatState = Low)
• 3rd level (BatState = Critical)