Battery management
SMA
Solar Technology AG
122
SI2012_2224-TEN082311
Technical Description
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 useable capacity of batteries is significantly reduced at temperatures below the
nominal temperature.
In the case of lead acid batteries the nominal capacity is adjusted by a fixed factor of –1 %/°C. In
the case of NiCd batteries a factor of –0.75 %/°C is used.
12.4 Charge Control
The Sunny Island uses a 3-phase charge control, using the IUoU procedure. When the device
operates with the public grid, there is also an optional fourth phase called silent mode.
The I stands for the bulk phase (I phase). In this phase, charging is limited by the maximum defined
battery current ("222.01 BatChrgCurMax" parameter), the nominal grid current
("232.03 GdCurNom" parameter) or the maximal AC charging current of the Sunny Island
("210.02 InvChrgCurMax" parameter).
In each case, whichever of these values is reached first functions as the limiting value. During this
phase, the battery's voltage increases as its state of charge increases.
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.
