Guidelines for Lithium Battery Pack Protection Board (BMS)

When the continuous discharge current is generally less than 200A, the maximum voltage of the battery pack does not exceed 100V, and the customer does not have special requirements for battery information communication, a common protection board solution can be selected. The performance requirements for the protective board are as follows:

Balance function
1.1 Common balancing functions: A. End balancing function; B. Real time voltage difference balancing function.

1.1.1 Ternary lithium batteries do not use the A balancing function and can choose the B balancing function.

1.1.2 Lithium iron phosphate batteries should use B balancing function as much as possible; Can the A balancing function be selected, with a fixed point voltage of 3.50? 3.60V.

1.1.3 Is the equilibrium current 30? 100mA. The heating temperature rise of the balanced circuit shall not exceed 40 degrees.

1.2 Temperature detection and protection

1.2.1 The optimal charging temperature range is 0-45. If it exceeds the normal temperature range, charging will be stopped. The temperature detection accuracy is ± 5. Optional charging with high temperature protection of 45 ± 5.

1.2.2 Optimal discharge normal temperature range? From 20 to 60, if the temperature exceeds the normal range, discharge will be stopped, and the temperature detection accuracy is ± 5. Optional high temperature discharge protection of 65 ± 5.

1.3 Overcharge protection during charging

1.3.1 Overcharge protection voltage of lithium cobalt oxide, ternary material single cell battery 4.20? 4.25V, overcharge protection voltage accuracy 25mV.

1.3.2 Overcharge protection voltage of single lithium iron phosphate battery 3.70? 3.90V, overcharge protection voltage accuracy 25mV.

1.3.3 The overcharge protection voltage of a single lithium titanate battery is 2.80V-2.90V, and the accuracy of the overcharge protection voltage is 50mV.

1.4 Discharge Overdischarge Protection

Is the over discharge protection of lithium iron phosphate material cells 2.0? 2.5V, over discharge protection voltage accuracy 80mV.

1.4.2 Lithium cobalt oxide, the over discharge protection of ternary battery cells is 2.5? 3.0V, overvoltage protection voltage accuracy 80mV. According to the battery cell specification book, define the overvoltage protection voltage.

1.4.3 The over discharge protection of lithium titanate battery cells is 1.4-1.5V, with an over discharge protection voltage accuracy of 80mV. Adjust the overvoltage protection voltage according to the actual situation.

1.5 Overcurrent protection

1.5.1 Discharge overcurrent protection is available, and the delay value of overcurrent protection is defined according to specific projects.

1.5.2 Charging overcurrent protection is available, and the delay value of overcurrent protection is defined according to specific projects.

1.6 Short circuit protection

1.6.1 Output short-circuit protection is available, and the delay value of short-circuit protection is defined according to specific projects.

1.7 Self consumption design

1.7.1 Ordinary hardware protection board, self consumption requirement<100uA.

1.7.2 Protection boards with special functions such as electrified communication shall have a self consumption requirement of less than 200uA. For special projects with self consumption greater than 200uA, engineers will adjust the requirements according to the project.

1.8 Conduction internal resistance

According to the specific product definition, the conduction internal resistance of the protective board should have a full load temperature rise of less than 40 degrees.

1.9 Continuous current

1.9.1 Rated continuous discharge current, with a temperature rise of less than 40 degrees for all components.

1.9.2 Maximum continuous discharge current, operating for 20 seconds without protection, with a temperature rise of less than 50 degrees for all components.

1.9.3 Continuous charging current, with a temperature rise of less than 25 degrees for all components.

1.10 Temperature rise

1.10.1 The maximum temperature rise of heating elements such as resistors and MOS should be less than 50 ℃, and they should be discharged and charged at the maximum current that can continue to operate.

1.11 Output anti reverse connection function

1.11.1 Optional protection board output with anti reverse connection function

1.12 Voltage resistance

When the charging voltage at the input end is 1.2 times higher than the normal charging voltage, it is required that the protection board cannot be damaged.

1.13 Fuses

Is the circuit equipped with a FUSE fuse, and the continuous operating current of the FUSE fuse is 1.25 times the normal operating current? 1.7 times, and the FUSE fuse cannot be turned off during PCM overcurrent protection.

1.14 Wire current carrying capacity, color marking, and wire number marking

1.14.1 The current carrying capacity of the wire is designed based on a long-term load current of 4A for 1 square copper core wire

1.14.2 The positive electrode for battery charging and discharging is defined as red; The negative electrode of battery charging and discharging is defined as black;

1.14.3 Different potentials of voltage detection lines need to be distinguished by color, and the color of batteries below 8 strings (including 8 strings) is not allowed to be repeated; The color type of batteries with 8 or more strings can be determined based on the specific situation of the project. For example, 10 strings of batteries can be marked with 5 colors; Repeat the sorting after arranging 5 different voltages; The identification of auxiliary wire numbers can ensure the foolproof and reliable wiring.

1.14.4 Voltage detection lines, wire harnesses with different potentials need to be distinguished and described using wire numbers. The wire numbers are arranged in order from high potential to low potential: 1, 2, 3, 4; Wire harnesses with plugs can be labeled with wire numbers at the plug end, but wire numbers must be added at the wiring end; Wire harnesses without plugs need to be labeled with wire numbers at both ends to prevent confusion.

Design of management system

The battery management system is closely integrated with the battery, constantly detecting the voltage, current, and temperature of the battery. At the same time, it also performs leakage detection, thermal management, battery balance management, alarm reminders, calculates remaining capacity and discharge power, reports SOC&SOH status, and uses algorithms to control the maximum output power based on the voltage, current, and temperature of the battery, as well as using algorithms to control the charger for the best charging current,

Real time communication with the main controller, energy control system, display system, etc. is achieved through communication bus interface.

BMS system functions

The general BMS management system has the following functions, and different projects can flexibly adjust parameters and functions according to the situation;

1) Thermal management (high and low temperature detection and protection); Generally, projects that do not involve low-temperature charging should avoid heating management as much as possible; Try to use physical measures such as air cooling or water cooling for overall heat dissipation;

2) Balanced management; There are two types of balancing: active balancing and passive balancing. Products with larger capacity should prioritize active balancing.

3) Capacity calculation SOC; By integrating the discharge curve of the battery with the load voltage and current, the SOC can be dynamically estimated; The power battery should be controlled within 10% error; Energy storage batteries should be controlled within a 5% error;

4) Alarm reminder; Display various information of the battery pack (voltage, current, temperature, SOC, charging status, charging faults, etc.) on the display screen, or transmit it to the upper computer through communication; When a malfunction occurs, the buzzer sends an alarm prompt to the user, and the specific type of malfunction is displayed on the display screen simultaneously; It can also be adjusted according to customer requirements and the actual situation of the project.

5) Power detection; Generally, it is necessary to upload the operating conditions to the upper computer for analysis.

6) Voltage detection; By isolating and amplifying the voltage of the series connected individual cells, real-time detection of the voltage of each cell is achieved, with a voltage detection range of 0-5V and a detection accuracy of ± 5mV.

7) SOC&SOH status detection; Based on the performance indicators detected during inspection, the health status of the battery can be analyzed.

8) Display system; Can display voltage, current, temperature, SOC, charging status, charging faults, etc.

9) Communication function; Design communication types and functions according to customer requirements.

10) Leakage detection;

11) Optimal charging current control;

12) System self check;
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