SMA SI 3324 - Manual (Page 39)

SMA Technologie AG Battery Management
User Manual SI3324/4248-14:FE2406 Page 39
6.3 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. 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)
The following figure shows the four battery states:
As long as the Sunny Island 3324/4248 has not detected a deep discharge then it
is in the battery state (BatState) Normal.
As soon as the first level of deep discharge is reached, the Sunny Island 3324/4248
switches to the Warning state. This can be used to start a generator.
If the batteries are further discharged despite the warning, then the battery state now
jumps to the next deep discharge level Low. If desired, this level can be used to
trigger the Sunny Island 3324/4248 relay contact to switch off all or some of the
loads.
Normal
Warning
(Start
Generator)
Low
(Load
Shedding)
Critical
(Shut
down)
BatVoltage, BatCurrent >
SocLim1
for t > 15 minutes
BatVoltage, BatCurrent >
SocLim2
for t > 15 minutes
BatVoltage, BatCurrent >
SocLim3
for t > 15 minutes
or charge current
BatVoltage, BatCurrent <
SocLim1
for t > 2/6/30 minutes
BatVoltage, BatCurrent <
SocLim1
for t > 2/6/30 minutes
and no charging current
BatVoltage, BatCurrent <
SocLim2 for t > 2/6/30
minutes
100 %
SocLim1
SocLim2
SocLim3
0 %