ABSTRACT
Safety is a primary concern of any battery management system.29 This is espe cially true for Li-Ion systems, since the chemistry is potentially flammable under abuse conditions.30 The chemistry does not have a limit to the charge voltage under constant current so steps must be take to ensure the cells are maintained in a safe operating range. Limiting the voltage range, however, could have an impact on the available capacity to the system. Figure 16.17 shows that battery capacity can vary by over 10% with just a lOOmV difference in charging voltage. If the voltage were allowed to rise above the optimal point, cycle life suffers, and if severe enough, can cause the system to plate lithium metal, severely reducing capacity and possibly causing a safety problem.31 Figure 16.8 shows an outline of the protection circuit and typically has overvoltage cutoff tolerances between 25mV and 50mV. The protection circuit is permanently attached to the cells in the pack; therefore, the operating current must be extremely low, typically in the tens of microamps.
