SMA Solar Technology AG Battery Management
Technical Description SI5048-TB-TEN110340 99
The battery's state of health (display value "320.01 Soh") is a measurement of the present useable
capacity expressed as a percentage relative to the nominal capacity. 100 % means that the entire
nominal capacity can be used. 50 % means that only half of the original nominal battery capacity
can be used. The battery's state of health is also calculated by means of a self-adapting method which,
however, can only produce good and exact values after a number of charging cycles.
The present capacity for the Sunny Island is automatically adjusted downwards for temperatures <
20 °C, since the usable capacity of batteries is significantly reduced at temperatures below the
nominal temperature.
In case of lead acid batteries, the nominal capacity is adjusted by a fixed factor of –1 %/°C.
For NiCd batteries, a factor of –0.75 %/°C is used.
13.4 Charge Control
The Sunny Island uses a 3-phase charge control, using the IUoU procedure. When operating with the
power distribution grid, a fourth level, Silent Mode, is optionally available.
The I stands for the constant current phase (I phase). In this phase, the charging is limited by the
maximum defined battery current (parameter "222.01 BatChrgCurMax"), the nominal grid current
(parameter "232.03 GdCurNom") or the maximum AC charging current of the Sunny Island
(parameter "210.02 InvChrgCurMax"). The respective value reached first is the limiting value.
During this phase, the battery voltage increases as the battery is charged.
Once the battery voltage reaches the predefined value for the second phase Uo
("222.07 — 222.09", ChrgVtgBoost or ChrgVtgFul or ChrgVtgEqu parameters), the constant voltage
charging (absorption phase) begins.
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