Blog - LiFePO4

The BMS2405 - basic information

General function

• Battery management system for Li-Ion, LiFePo4 and LiPo chemistry cells
• Protect and balance cells during charge and discharge
• Measure SOC (remaining charge/energy in battery)
• Fully balance cells in single charging cycle if charger is not disconnected
• Integrated display which shows:
• —>  Mode (Charge, Discharge, Full, Error)
• —>  Current state of battery 0-9

Cell balancing

• Passive balancer with resistor across each cell. Balancing algorithm is executed only in charge mode.
• Integrated discharge resistors for each cell. Resistors cooled to back plate.
• Adjustable balancing parameters:
• —> Minimum difference voltage between cells to turn on balancing resistor
• —>  Minimum cell voltage for balancing (prevents balancing in early in charge cycle)
• Smart overheating protection – balancing resistors on cells with biggest voltage difference will be disconnected later as on cells which have smaller voltage difference.

Charging mode

• Monitoring of each cell voltage during charge
• Integrated charger disconnect relay to prevent battery overcharging
• Input for two temperature sensors (standard 10 kOhm NTC)
• If charger is connected after battery is fully charged, cells are continuously balanced. No need to do more charging cycles to balance all cells to 100%.
• Charger detect with separate input or detection of voltage on charger input connector.

Discharge mode

• Monitoring of each cell voltage during discharge
• Integrated ignition switch, which disconnect ignition line in case of empty battery – when first cell reaches minimum voltage
• Adjustable low voltage cell limit

SOC monitoring

• Requires external battery current sensor (standard current hall probe – recommended
• Monitoring of charge and discharge current and calculation SOC
• Automatic adjustment of SOC when battery is fully charged or totally discharged
• Analogue voltage output for connection of external battery state display.

Battery monitoring

• Measures next battery data:
• —>  total battery voltage
• —>  battery current
• —>  up to 2 x battery temperature, internal circuit temperature. Requires inexpensive NTC resistors for temperature sensing
• —>  Min and max cell voltage and cell ID
• —>  SOC (in %, user adjustable total battery capacity)
• Battery data is send over serial port to controller. Additional can be send to programming RS232 connector for external logging devices connection.
• Records battery historical data for maintaining and supervision:
• —>  number of charge cycles
• —>  number of deep discharge cycles
• —>  total accumulated charge out (in Ah)
• —>  min and max temperature for all thermometers
• —>  min cell voltage and cell ID

Specifications

• Works with 16 or 24 cells Li chemistry batteries. User setting of number of cells (from 6 to 24)
• Balancing current 0,5 A per cell
• 30 A charger relay
• 5 A ignition switch (for disconnecting motor controller when battery is empty)
• <100 uA standby power consumption
• Dimensions 188 x 106 x 35 mm , weight 0,55 kg
• Operating temperature -20/+65 *C, heat sink temperature protection at 80 *C.