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4.9. Battery discharging
During discharge, the BMU monitors the battery physical parameters (cell voltages, current and
temperature) and informs the application via the CAN Open bus about the maximum current
authorized for discharge (IMD) and the minimum voltage allowed for discharged (VMD), warning
and alarms.
The BMU sends the IMD and VMD values on the CAN Open bus in real time.
IMD depends on 2 parameters:
o
Battery temperature
o
Battery SOC
It is important to note that this dependency is only made to ramp down the power in order to
avoid a sudden opening of the battery contactor (see alarms description in in §16, Appendix III).
Nota: IMD will never exceed 50A continuous.
4.10. Complete discharge & sleep mode
When a full discharge has been performed, it is recommended to charge the battery
immediately or, if not possible, to switch OFF the 24VDC supply in order to stop the internal
consumption of battery electronics.
If the system is not switched OFF and if one cell voltage is below 3.325V during 2 hours (see
§4.5), the BMM will automatically put the system in
SLEEP
state. To restart the system when it
is in
SLEEP
state, send a RESET frame by CAN bus which is still alive.
In usage conditions, the discharge is limited to 2.7V on the first cell voltage reached: the BMM
sends the corresponding warning fault code. If the discharge continues and if one cell voltage
goes below 2.5V, a critical fault is sent and the battery contactor is opened (see §4.2.2).
If one cell is over-discharged (< 2V), the battery is out of order and SAFT shall be contacted.
For lithium-ion technology, when the cell voltage reaches a very low value, the battery may be
no longer operational. The alarm value includes tolerance, but under this limit the battery life
cannot be guaranteed.
4.11. Alarms and warnings
The BMM sends on the CAN Open bus the code faults (warnings or alarms) to the application
(see alarms description in §16, Appendix III).
For example, during a discharge if one cell reaches 2.7V, the BMM will send code fault and the
converter has to stop the discharge. If the discharge continues and one cell reaches 2.5V, the
BMU will open the battery contactor.