SMA SI 3324 Installation - Manual (Page 104)

Battery Management SMA Technologie AG
Page 104 SI3324/4248-14:SE2406 Installation Guide
The Sunny Island 3324/4248 initiates a full charge every 14 days ("24-13
TcycleFull" parameter) or after every eight charging throughputs, with the aim of fully
recharging the batteries to remove any negative effects caused by insufficient
charging. Various studies have shown that regular full charging every two to four
weeks can double the battery service life in off-grid systems.
A battery bank consists of many series-connected individual battery cells (2 V each),
each of which having a slightly different behavior. Over time, this results in different
charge levels of the individual cells. This can lead to premature failure of first single
cells and then failure of the entire bank.
For this reason, the Sunny Island 3324/4248 automatically performs regular
equalization charging every 60 days ("24-14 TcycleEqual" parameter) 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 %.
If equalization charging begins directly after or during a normal or full charge, then
the time spent in the absorption phase of the previous charging process is taken into
account in the subsequent charging process. The same applies to full charging.
If the batteries are charged by an external charger or charge controller and the
criteria for a full charge or equalization charge are satisfied, then the Sunny Island
3324/4248 treats this as if it had performed the full charge or equalization charge
itself.
In addition to automatically switching between the charging processes (normal, full,
equalization and float charging) you can also manually set the Sunny Island 3324/
4248 to use any charging process. This is done using the "40-1 BatChargeMode"
parameter in the "Operation" menu.
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).