Boost Charge; Full Charge - SMA Sunny Island 2012 Technical Description

Battery management
Charging voltage change
The charging voltage does not rapidly change, but is slowly adjusted to the new nominal
value by approx. 0.5mV/cell*s as the constant voltage phase changes to the float
charge. This also takes place if the nominal value is changed manually.
The charging capability of batteries is highly dependent on the battery temperature. For
temperatures < 20°C, the charging voltage must be slightly increased, and for temperatures
> 20°C it must be slightly decreased. This is necessary to prevent overcharging and insufficient
charging reliably and at all battery temperatures. For this reason, the Sunny Island is equipped with
automatic temperature compensation of the charging voltage. The charging voltage is adjusted by:
• 4 mV / °C and cell, in the case of VLA and FRLA battery types.
• 0 mV / °C and cell, in the case of NiCd batteries.
The temperature compensation value can be set using the "222.11 BatTmpCps" parameter.

12.4.1 Boost Charge

The boost charge is the most common charging process of the Sunny Island. The boost charge
ensures high generator capacity utilization 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
homogenizing the electrolytes. The boost charge process can charge the battery up to approx.
85 % to 90 %.

12.4.2 Full Charge

Every 14 days or 8 nominal charge throughputs, the Sunny Island initiates a full charge
automatically (parameter "222.05 CycTmFul").
Nominal Charge Throughput
A nominal charge throughput is reached when the sum of the discharge currents
corresponds to the rated capacity of the battery.
Example: the battery has a rated capacity of 100 Ah. A nominal charge throughput is
reached when the battery has been discharged 10 times for 1 hour by 10A.
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. A regular full charging every two to four weeks can double
the battery service life in off-grid systems.
124 SI2012_2224-TEN082311
SMA Solar Technology AG
Technical Description