SMA SI 4548-US - Manual (Page 111)

SMA America, LLC 13 Battery Management
Operating Manual SI4548-6048-US-BE-en-20 111
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 (parameter
"222.10 ChrgVtgFlo"). 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 to 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:
• VLA and FLRA battery types: 2 mV/°F (4 mV/°C) and cell
• NiCd battery types: 0 mV/°F (0 mV/°C) and cell
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.