SI4548-US-10 Manual

13 Battery Management SMA America, LLC
108 SI4548_6048-US-TB_en-13 Technical description
Since full charge states are generally only rarely achieved during a grid failure, the operation used
here can also utilize the battery voltage during constant discharge phases with low discharge currents
to recalibrate the state of charge. Compared to the ampere-hour balancing method, the operation
used here exhibits a high level of stability over the long term when recalibrated at regular intervals.
Both the ampere-hour balancing method and the recalibration procedure, which is performed via the
voltage, automatically adjust to the connected battery over time (depends on the number of grid
failures).
The estimated state of charge error (display value "120.11 BatSocErr") will provide you with
continuous information on the accuracy of the battery state of charge currently calculated.
The average error will continuously diminish as the adjustment to the actual battery state of charge
increasingly improves.
State of Health (SOH)
Only when the battery is new does its usable capacity correspond to the capacity specified by the
battery manufacturer. As the battery ages and as a result of frequent insufficient charging, the usable
battery capacity may decrease considerably on a permanent or only temporary basis.
The battery 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 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
< 68°F (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 ‒0.6%/°F
(‒1%/°C). For NiCd batteries a factor of − 0.4%/°F ( − 0.75%/°C) is used.
Recalibration of the State of Charge
The Sunny Island recalibrates the display value for the state of charge of the battery to 20% as soon
as the battery voltage per cell has reached a limiting value that is dependent on the battery type and
the battery capacity. In addition, recalibration of the state of charge always takes place if one of the
following conditions is met:
• The nominal capacity is entered incorrectly.
• The battery cable resistance is too high.
• The battery is not connected correctly.
• Differing concentrations of acid in FLA batteries (if necessary reset the parameters in the menu
"222# Battery Charge Mode).
• The battery has aged so much that the SOH is below 80%.