The battery management system (BMS) plays a defining role in how well a battery stack meets each of these design challenges. At the heart of the BMS is a battery monitoring integrated circuit (IC). This IC measures individual cell voltages which are used to determine state of charge and battery stack health.
The most critical characteristics of a battery monitor IC are accuracy, data robustness, and fault detectability to ensure safety. The accuracy of the monitor IC directly affects system cost, battery pack reliability and lifetime. Each cell has a limited capacity which must be carefully managed. Overcharging can cause safety and reliability issues, while over-discharging can affect the lifetime of the cell. Using a less accurate monitor IC requires that the system designer use larger “guard bands” to protect against overvoltage and undervoltage, therefore limiting the amount of total available capacity for the vehicle. A higher accuracy monitor IC can make use of more or each cell’s total capacity, reducing the total cost of the battery stack system.