In August, four government ministries jointly issued a safety notice on new energy vehicles to highlight the compulsory installation of battery management system (BMS) in plug-in hybrid and electric vehicles.
But many domestic battery manufacturers do not attach much importance to BMS. They are pursuing the cost reduction at the cost of function and performance, which leaves hidden safety risks.
The fire accident of a Zoyte electric taxi in June in Hangzhou was found to be caused by battery problem. The fire was ignited by short circuit problem as a result of battery leakage because batteries failed to function well when they were connected in battery packs.
“There is no big technology gap in battery cell manufacturing between China and foreign counterparts. But many domestic battery makers are poor in manufacturing battery packs, in which the consistency is hard to be guaranteed,” said Ma Xiaoxiao, a Beijing-based EV company executive.
Though the country so far does not have unified BMS testing standards, domestic manufacturers have developed their independent corporate standards, which will be further perfected with technology advancement, said Zeng Lingpeng, deputy general manager of Chery New Energy Automobile Technology Company.
BMS cannot be 100 percent safe
BMS can monitor the operation of battery cells and the pack, prevent batteries from over charge or discharge and expand their cycle life. In case of the accidents, BMS can warn the drive of the danger in advance.
Specialists said BMS is of the same importance as the quality of battery packs, they are crucial to the prevention of battery fire accidents. Without good management of BMS, local power consumption overcapacity would lead to local heat that could cause spontaneous combustion.
However, BMS functions only as a monitor instead of a problem solver, said battery specialist Yang Zhiwei. The Zoyte electric car that caught fire in Hangzhou actually had BMS installed inside. Yang said even if BMS notifies the driver of the battery faults, disaster is not easy to be avoided if no expertise is shown on part of the driver. That means safety is finally dependent on unquestionable quality of the batteries.
“China lacks basic technical parameters and standards on BMS and there are no authoritative agencies to test the quality of BMS developed by a variety of manufacturers,” said a Shanghai-based electronics expert Han Jingke.
According to Yang Zhiwei, China has a dozen of domestic BMS developers who are working separately but in western countries there is only one or two provider of BMS with a high degree of specialization, including U.S.-listed companies Texas Instruments, O2Micro and linear Technology. Domestic battery providers generally use homemade BMS which is cheaper but inferior in stability and safety.