Circuit design of serial port and CAN communication module used in 18650 lithium 3.7 battery management system

　　Serial communication module: The 18650 lithium 3.7 battery management system sends the collected and processed data to the PC interface through the serial port to realize human-computer interaction. Through the serial port interface, you can observe the total voltage, cell voltage, current, SOC, fault status, charge and discharge power and other parameters of the battery. You can also send it through the serial port to achieve online calibration of the management system. Its hardware circuit is mainly based on the MAX232 chip, as shown in Figure).

　　MAX232 is a transceiver with +5V power supply. It is connected to the computer serial port to realize level conversion of RS-232 interface signals and TTL signals, so that the BMS and PC can carry out asynchronous serial communication. In order to prevent electromagnetic interference from affecting data transmission on the serial port, the bus signal must be isolated. The serial port is a one-way transmission, so it is more convenient to use 6N137 photoelectric coupling) The 232TXD signal optocoupler isolation circuit is shown.

　　CAN communication module: CAN communication is an information bridge between the 18650 lithium 3.7 battery management system (BMS) and the vehicle HCU. The BMS sends the 18650 lithium 3.7 battery status parameters to the HCU through the CAN bus. The HCU makes decisions by judging the current 18650 lithium 3.7 battery status. Distribute power between the motor and engine and control the charge and discharge of the battery. At the same time, the BMS can also receive relevant commands from the HCU and handle them accordingly. In terms of hardware, it mainly provides differential sending capabilities for bus data and differential receiving capabilities for communication bus data through the pCA82C250 universal CAN transceiver. The anti-interference ability on the CAN bus is enhanced through an optocoupler isolation circuit similar to the figure). Its hardware circuit is shown in the figure.

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