As an important energy unit in the fields of electric vehicles, electric tools and energy storage systems, the state monitoring and management of power batteries are crucial to safety and performance. In order to realize efficient and stable communication of power battery pack, RS-485 (I .e. 485 communication) is widely used due to its strong anti-interference ability, long transmission distance, flexible networking and other advantages. This article will fully explain the 485 communication scheme of power battery, covering the basic principles, hardware design, electrical connection, protocol design and common problem handling of 485 communication, help readers fully understand and apply this communication scheme.

I. Overview of RS-485 Communication Foundation

1. RS-485 communication features

RS-485 is a differential signal communication standard with the following main features:

• strong anti-interference ability: differential signal transmission can effectively resist common code interference.
• Long transmission distance: under standard conditions, the transmission distance can reach 1200 meters.
• Multi-point communication: supports up to 32 drivers and 32 receivers attached to the same bus, suitable for networking applications.
• Variable rate: The common speed ranges from several kbps to 10Mbps, which can be flexibly selected.

2. Application of RS-485 in power battery management system

the power battery management system (BMS) needs to collect the voltage, temperature, current and other information of the battery cell in real time, and upload the data to the main control unit. RS-485 communication can meet the needs of long-distance and multi-node data transmission and ensure the stability and accuracy of data. It is an ideal choice for communication between modules in the power battery pack.

II. Power battery 485 communication hardware design

1. Communication interface circuit

power Battery 485 communication interface circuit mainly consists of differential driver and receiver. Common chips include TI SN75176, MAX485, and SP3485.

• Differential driver: converts single-ended TTL signals into differential signals (two lines A and B) to improve anti-interference capability.
• Differential receiver: restores differential signals to TTL signals for MCU processing.

2. Bus structure design

RS-485 bus uses Twisted pair as transmission medium, twisted pair can further reduce electromagnetic interference. In the power battery pack, each battery management module is connected in series through twisted pair to form a bus structure.

3. Terminal matching resistance

in order to prevent signal reflection, a 120Ω terminal matching resistor is usually connected at both ends of the bus. If no matching resistor is installed on the terminal, the signal may be distorted, resulting in communication errors.

4. Power supply and protection of 485 transceiver

due to the complex environment of power battery, the communication interface circuit needs to design regulated power supply and overvoltage protection circuit to prevent electromagnetic interference and overvoltage from damaging the chip. At the same time, it is recommended to install TVS diode or common mode choke coil on Line A/B to enhance anti-interference capability.

III, power Battery485 communication electrical connection scheme

1. Definition of differential signal line

• line A (non-inverting)
• B line (inverted)

when designing, make sure that all devices have the same definition of lines A and B, otherwise the communication cannot proceed normally.

2. Wiring mode

• bus topology: RS-485 we recommend that you use a bus structure to connect all devices in parallel on the same twisted pair to avoid branch lines and reduce signal reflection and interference.
• Cable selection: it is recommended to use shielded twisted pair and ground the shielding layer to further suppress external interference.
• Grounding design: The system shall ensure common reference ground wire to avoid short circuit of ground connection. Meanwhile, the ground wire should be thick and short to reduce the grounding resistance.

3. Node address allocation

multiple modules in the power battery pack are connected through 485 communication, and each module needs to be assigned a unique address to realize master-slave communication. The address can be configured by hardware dip switch or software.

IV. Power battery 485 communication protocol design

1. Communication mode

the master-slave mode is commonly used, that is, the master control unit acts as the master station, sending requests to each battery management module (slave station) at regular intervals, and the Slave Station responds to data. This mode is simple and efficient to avoid bus conflicts.

2. Data frame structure

power Battery 485 communication data frames generally include:

• frame Header: identifies the beginning of the frame, which is convenient for the receiver to identify.
• Address domain: indicates the data destination module address.
• Function Code: distinguish different commands, such as read voltage and write parameters.
• Data Domain: contains actual collected or controlled data.
• Check code: Common CRC checks ensure data integrity.

3. Communication rate and time series

the communication rate is generally 9600bps or 115200bps based on system requirements and cable length. Time series design should reserve sufficient processing delay to avoid data loss.

4. Error detection and retransmission mechanism

the CRC check is used to detect data errors. When errors are found, the primary station should resend the request to ensure accurate and reliable communication data.

V. Common problems and solutions of power battery 485 communication scheme

1. Abnormal communication caused by signal interference

solution:

• use shielded twisted pair
• add terminal matching resistor
• add anti-interference protection components, such as TVS diode and common mode choke coil

2. Communication conflicts caused by address conflicts

ensure that each node address is unique and uses hardware dip switch or software configuration management address.

3. Long communication distance signal attenuation

use repeater or reduce the communication rate to ensure signal integrity.

4. Communication protocol mismatch or timing error

the communication frame is designed in strict accordance with the protocol, and the communication timing is adjusted to ensure smooth communication between the master and the slave.

VI. Brief introduction of instance application

take a 48V power battery pack as an example and connect 10 battery management modules with RS-485 communication:

• each module is equipped with MAX485 chip and connected to the same twisted pair bus.Each end of the bus is connected with 120Ω matching resistor.
• The master-slave communication protocol is adopted, and the master control unit periodically polls the data of each module.
• The data frame adopts the frame header + address + function code + data + CRC check format.
• Abnormal retransmission and data verification are realized through software.

This scheme realizes the real-time transmission and centralized management of data of each module in the battery pack, greatly improving the stability and safety of the system.

Power Battery 485 communication scheme has become an indispensable communication scheme in power battery management system due to its advantages of strong anti-interference ability, flexible networking and long transmission distance. Through reasonable hardware design, electrical connection and protocol formulation, combined with effective treatment of common problems, efficient and reliable data communication in the power battery pack can be realized, ensure the safe operation and performance optimization of the battery system.