Due to the recent news about fires caused by slow charging of the EV6, let's try to understand the root causes of these fires. Typically, fire incidents during electric vehicle charging do not occur under normal circumstances. The Battery Management System (BMS) itself has a power cut-off function, and the On-Board Charger (OBC) may or may not have this function depending on the manufacturer. I am not sure if the Everon slow charger had a power cut-off function, but generally, slow chargers passively supply power and there is no way to know how much charge is being supplied by a typical slow charger. While there is a method of communicating with the vehicle using PLC (Power Line Communication), I believe this feature is not yet available. Even if this feature existed, it would not be easy for a charger company to form a team capable of developing an algorithm to predict the internal state of the battery like the BMS does, so it is expected that they would simply use the values sent by the BMS.
Typically, fire problems during charging arise from discrepancies in the State of Charge (SOC) and the State of Health (SOH) as calculated by the BMS. For example, the BMS may calculate an SOC of 100%, but the actual SOC could be 105%. Although a margin of error of about 5% is generally allowed, this margin is determined through limited sample testing, so there could be cases where the error margin exceeds expectations. Another issue is when a cell underperforms compared to its specifications. Although cells have tolerances during manufacturing, sometimes cells that are below the minimum specified values are used. Moreover, it's impossible to test the degradation rate when the cells are shipped from the factory, so the degradation rate is unknown. Especially in summer, when the temperature is high, if the charge level reaches 100% and the cell temperature exceeds 30 degrees Celsius, the degradation rate increases. An increased degradation rate means a higher probability of fire.
Additionally, some manufacturers do not measure the SOC or SOH for each cell individually, but only for the entire battery pack. This makes it impossible to detect cells that are degrading more quickly, which can be problematic. Of course, since Hyundai is a reputable company, it is expected that they would predict the status of each cell individually.
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