The failure of a battery cell is not only related to the battery itself, but also to the failure of the battery management system BMS. BMS failure modes can also cause serious accidents in the following categories:
1. Failure of BMS voltage detection will cause the battery to overcharge or overdischarge:
The voltage detection wire has failed due to poor connection, crimping process, or poor contact. The BMS has no voltage information and should not stop when charging stops.
In addition, overcharging can easily cause the electrolyte in lithium-ion batteries to decompose and release gas. Even in severe cases, even smoke and fire can cause the battery to swell. Excessive battery discharge will damage the molecular structure of the battery's positive electrode material, making it impossible to discharge. At the same time, the battery voltage is too low, which will cause the electrolyte to decompose, dry the lithium precipitation, and return to the battery short circuit problem. When designing the system, a reliable voltage acquisition line should be selected during production and strictly controlled to prevent the voltage acquisition line from malfunctioning.
2. BMS current detection failed:
The Hall sensor fails, the BMS cannot collect current, cannot calculate SOC, and has a large deviation. Failure of the current detection may cause excessive charging current. Large charging current, the internal heat of the battery and the temperature exceeding a certain temperature will weaken the curing ability of the separator and seriously affect the battery life.
3. BMS temperature detection fails:
Failure to detect temperature will cause the battery to be used at excessively high temperatures, and the battery will undergo an irreversible reaction, which has a great impact on battery capacity and internal resistance. The battery's calendar life is directly related to temperature. The number of cycles at 45 degrees is half that at 25 degrees. In addition, when the temperature is too high, the battery is prone to bulging, leaking and exploding. Therefore, during use, the battery temperature must be strictly controlled between 20-45 degrees Celsius. In addition to effectively improving battery life and reliability, it can also effectively avoid short circuits and high temperature thermal runaway caused by low-temperature charging and battery lithium precipitation.
4. Insulation monitoring failed:
If the power battery system is deformed or leaks, insulation failures can occur. If BMS is not detected, an electric shock may occur. Therefore, BMS systems have the highest requirements for monitoring sensors. Avoiding the failure of the monitoring system can greatly improve the safety of the power battery.
5. Communication failure of electromagnetic compatibility problem:
For BMS systems, electromagnetic compatibility mainly tests its ability to resist electromagnetic interference. Electromagnetic interference will cause BMS communication to fail, causing the above problems.
6. The SOC estimation deviation is large:
Currently, the common problem for all BMS manufacturers is simply the difference in bias. Basically, current inspection standards require less than 5%. The BMS of most manufacturers should be difficult to implement because the SOC error will increase in actual use because the use environment is more complicated and the conditions that affect accuracy are more.
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