Ensures that the battery pack operates safely and reliably.
Prevents battery from operating outside of the safe operating area, calculate/reporting secondary data
Within the BMS, algorithms are run to generate accurate estimations of outputs, based on inputs
Redirects the recovered energy into battery pack
In EV’s, some noticeable amount of energy stored in the batteryis not shown at the dashboard, since it is reserved for hybrid operations
Ex: for the Mitsubishi Outlander PHEV (all versions/years of production), 0% of the state of charge presented to the driver is a real 20-22% of charge level
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More accurate for fuel gauges in EV’s, as it indicates expected run time, usage, and distance remaining
In the graph, an SOC(E) of 50% is achieved when the area underneath the curves (amount of energy supplied) is equal on both sides, which occurs at around 42% SOC(C)
Cell Configurations to Chargers
Series
Cells are connected in series, two-wire connect the positive and negative terminals to the respective ends of the series.
Example: Each cell in a 4s1p must be charged to 4.2 V (total 16.8 V is set for charger across the config). Ideally, each cell must be a charge to 4.2 V. However, it is possible that each cell is charged to different levels and at different rates (avoid this).
Example of a Commerical BMS (https://youtu.be/rT-1gvkFj60?t=163)
Consist of a balance connector that connects to each cell of the pack
Each cell is also connected to:
Two transistors
DW01A (Microsoft Word - DW01A-DS-10_EN.doc (escooter.org.ua)), which protects each cell from overcharge/discharge/current (below is a typical application circuit from DS)
Note the parasitic diode (RESEARCH THIS MORE) at M1. Even when M1 is off, charging is still possible due to this, since current flows from BATT- to BATT+ while charging. Conversely, if M2 is off discharging is possible due to M2’s diode, since current flows from BATT+ to BATT-
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Each cell is also connected to a BB3A (HY2213 Datasheet 範本 (hycontek.com)), for charge balance control (to ensure that each cell is charged to the same maximum voltage). Below is an example circuit of a cell (N-MOSFET)
When the battery voltage exceeds the overcharge detection voltage, the OUT pin outputs the logic HIGH to discharge the battery through the resistor. When the battery voltage dips below the overcharge release voltage (VCR), the OUT pin outputs logic LOW to turn off the N-MOSFET.
Near the battery pack are 6 Power N-MOSFET’s (N-channel 75V - 0.0095 - 80A - TO-220 - TO-220FP - D2PAK STripFET™ II Power MOSFET (digikey.com))
(Diagram at https://youtu.be/rT-1gvkFj60?t=313 )
When input current exceeds BMS lmit (calculated using voltage and shunt resistor), the certain voltage level activates a passive component network (RESEARCH THIS MORE), and turn off the MOSFET
NOTE: Most BMS include these 3 components, although some may omit the balance charging.