SMA America, LLC
Battery Management
Technical Description
SI5048U-TUS121440
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The charging capability of batteries is highly dependent on the battery temperature. For temperatures
< 77 °F (25 °C), the charging voltage must be slightly increased, and for temperatures > 77 °F
(25 °C) it must be slightly decreased. This is necessary to prevent overcharging and deep discharge
reliably at any battery temperature. For this reason, the Sunny Island is equipped with automatic
temperature compensation of the charging voltage.
The battery charging voltage is adjusted by:
• 2 mV/°F (4 mV/°C) and cell, in the case of VLA and FRLA battery types.
• 0 mV/°F (0 mV/°C), in the case of NiCd batteries.
The temperature compensation value can be set using the parameter ”222.11 BatTmpCps”.
13.4.1 Boost Charge
The boost charge is the most common charging process of the Sunny Island. The boost charge ensures
a high generator workload through a high charging voltage over a short period of time. With liquid
FLA lead acid batteries, this charge process should be used for gassing and thus compensating the
electrolytes. The boost charge process can charge the battery up to approx. 85 % to 90 %.
13.4.2 Full Charge
Every 14 days or 8 nominal charge throughputs, the Sunny Island automatically initiates a full charge
(parameter ”222.05 CycTmFul”).
The objective is to recharge the battery to a charge level of at least 95 % and to compensate the
possible effects of an insufficient charge. Regular full charging approximately every 2 to 4 weeks can
double the service life of the battery.
Nominal Charge Throughput
A nominal charge throughput is reached when the sum of the discharge currents
corresponds to the nominal capacity of the battery.
Example: The battery has a nominal capacity of 100 Ah. A nominal charge throughput is
reached when the battery has been discharged 10 times for 1 hour by 10 A.
Change to a Full Charge
If the Sunny Island changes to full charge after a specific time of boost charging has
elapsed, the entire time of boost charge elapsed is considered for the full charge.
More than 1% of the Nominal Capacity of the Battery will be Discharged
If more than 1 % of the battery's nominal capacity is discharged during a full charge, 50 %
of the time elapsed is considered for the next constant voltage phase.
External Charging Device
If an external charging device or charge controller is connected to the battery and the
criteria for a full charge are fulfilled due to external charging, the Sunny Island treats this
as if it had performed the full charge itself.
