13 Battery Management
SMA America, LLC
110
SI4548_6048-US-TB_en-13
Technical description
The following figure shows the relationship and the flowchart of the charging phases and charging
processes.
Once this constant voltage phase is finished, the Sunny Island switches to float charge which again
carries out constant voltage charging but at a greatly reduced charging voltage
("222.10 ChrgVtgFlo" parameter). The purpose of the float charge is to keep the battery in a fully
charged state without causing premature aging through overcharging. The Sunny Island remains in
this phase until either more than 30% of the nominal capacity has been used (all discharges are
added up) or the state of charge is below 70%. When the Sunny Island is operating on the utility grid,
it can also switch from float charge into silent mode.
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), and cell, in the case of NiCd batteries
The temperature compensation value can be set using the parameter "222.11 BatTmpCps".
Changing the charging voltage
The charging voltage does not change erratically. Instead, it slowly changes to the new setpoint
at a rate of approximately 0.5 mV/cell*s when switching from constant voltage charging to
float charge. This also happens if the setpoint is set manually.
Summary of Contents for Sunny Island 4548-US
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