4
C-Rate: Current normalized to the rated capacity of a
battery.
Cut-off temperature: Temperature where the BMS will
terminate the usage of the Battery Unit
Cut-off voltage: Voltage where the BMS will no longer
allow usage of the Battery Unit.
EOL: End-of-Life, as definition it states when less than
80 % of the initial capacity remain. Li-ion can be used for
lower remaining capacity.
LFP: Lithium iron phosphate, electrode material used in the
LITE Battery Unit.
SoC: State-of-charge, fraction of rated capacity, 0-100 %.
1.3
Unstable Mains Service
Where the main electrical supply is of poor quality, the
batteries are used to provide service when the mains is off.
Common to the poor grid operation are frequent
interruptions. Often the time between the interruptions is
short which means that the battery will not be fully
charged. This is not a problem for lithium-ion batteries, as
they have a stable performance, independent of SoC. The
figure below shows the voltage of battery units in unstable
mains.
2
Operation
2.1
GENERAL PRECAUTIONS
Only operate within specified temperature, current and
voltage. All data from battery shall be stored in an upper
host computer for future reference.
2.2
BMS
The NorthStar LITE Battery Unit is equipped with an
internal BMS in every unit. The BMS will protect the
battery from operating outside of its safe operating
window by monitoring cell voltages, currents, SoC, capacity
and temperatures. The BMS also include cell balancing
functionality, reverse polarity protection, charge control,
high/low temperature cut off, regulated slow charge, and
the optional heater on/off.
2.2.1 Protection functions
Overvoltage
Overvoltage
System
Cell
Rated charging voltage
52.5V
Overcharge alarm
54.0±0.5V
3.6±0.02V
Overcharge protection
54.6±0.5V
3.65±0.02V
Overcharge recovery
50.2±0.5V
3.4±0.02V
If the system voltage or cell voltage becomes higher than
the overcharge protection voltage for more than 2 seconds,
the BMS enters overcharge protection state and inhibits
charging.
The overcharge protection delay is 1 ± 0.5 s and the
overcharge protection release conditions are one of the
following:
The voltage is below the recovery voltage or
Switch to discharge mode.
Undervoltage
Undervoltage
System
Cell
Overdischarge alarm
39.0±0.5V
2.6±0.02V
Overdischarge protection
37.5±0.5V
2.5±0.02V
Overdischarge recovery
43.5±0.5V
2.9±0.02V
If the system or cell voltage becomes lower than
overdischarge protection voltage and stays at that voltage
longer than 2 seconds, the BMS enters overdischarge
protection state and inhibits discharging.
The overdischarge protection delay is 1 ± 0.5 s and the
overdischarge protection release condition is:
Start charge mode.
Sleep mode: If undervoltage protection on system level or
cell level is detected, the BMS goes into sleep mode.
Release conditions are one of the following:
Put in charge or
Activated via RS232 communication or
Reset button pressed
Overcurrent
Overcurrent
System
Charging Overcurrent alarm
102±3A
Charging Overcurrent protection
105±4A
Discharging Overcurrent alarm
102±3A
Discharging Overcurrent protection
105±4A
Short circuit current protection
210±10A
Voltage of battery in unstable mains
Time [Days]
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