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2.4
Discharge characteristics of Battery Unit
Since the voltage curve of cells containing LFP is very flat it
is hard to estimate the SoC with any higher accuracy from
just checking the voltage. See figure below.
Voltage
Voltage vs SOC for LFP
Time [Minutes]
The BMS is able to determine SoC, using a specially
designed algorithm. The SoC level of the Battery Unit is
indicated by four diodes lit up with a green light on the
front panel of the Unit. The calculated SoC can also be
retrieved through the PC SW or by any upper host
computer that is connected to the battery through the
RS485 port.
The LED indicators offer the following steps of SoC, see
table.
SoC %
0-25
25-50
50-75
75-100
vs SoC for LFP
LED indicators
2.5
Nominal Operating Temperature Range
Lithium-ion batteries operate over a wide temperature
range; however, this does not imply that any type of
usage is allowed for all conditions. The charging process
of lithium-ion batteries is more sensitive than discharging
and therefore charging is limited to only be allowed at
temperatures over 0°C and below 45°C. Discharge is
allowed between -20 to 60°C. If the temperature of the
Battery Unit exceeds any of these thresholds, the
operation will be restricted and then terminated, as a
safety precaution, until the temperature reaches within
the specified ranges. Operating the Battery Unit at
continuously high temperatures will cause premature
aging and shorten battery life. Never use the Battery Unit
outside the above specified temperature limits, as it
constitutes a safety risk.
Mode
Charge
Discharge
2.5.1 Low Temperature Performance
At temperatures below 15°C, the performance of the
Battery Unit starts to become affected. See figure in section
2.3 showing the capacity @ different temperatures. To
extend the performance range of the system, a heater is
available as an option.
2.6
Charge
The Battery Unit has excellent re-charge capabilities and
allows for full re-charge within only 1h 15min, from 0-100 %
SoC. For optimal battery usage, a recharging time of five (5)
hours is recommended, to provide best battery lifetime. For
a partially discharged Battery Unit, the charge time will be
less.
Lithium-ion batteries are sensitive to overcharging,
negatively impacting battery life and can, in the worst case,
lead to venting and thermal events. However, the BMS will
engage the charge cut-off, terminating the charge before
the Battery Unit reaches dangerous voltage levels. To
maximize the battery usage, a constant current-constant
voltage (CC-CV) charging regime is recommended, see
figure below. The normal working voltage area is 42V-
52.5V. However, if the Battery Unit is combined with
existing lead-acid batteries the charging will be terminated
by the BMS at a voltage of 54.6 V (corresponding to 3.65 V
per cell). When charging is completed, the BMS disconnects
the Battery Unit, leaving it at float voltage. Intermittent
charging will be initiated every time the Battery Unit has
been discharged a minimum of 5% (of its rated capacity).
Temperature range
0 – 45°C
-20 – 60°C
6
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