Battery Power - November 2011 - (Page 17)

To prevent thermal run away initiation, minimize retention of heat in the pack, including heat removal if required by high power activity. Prevent cell charging when cell temperature is below a cold temperature threshold (to avoid Lithium dendrite formation that can cause internal shorts) or above a high temperature threshold. The battery case should prevent damage from expected shock and vibration during transport and use, and minimize cell crush or penetration damage due to vehicle collisions. Provide for controlled release of excessive internal cell pressure in the battery case design. Use self extinguishing materials inside battery case. Consider installing a firewall between battery case and driver and passenger spaces. Fuse the battery to prevent electrical fire, spark, and shock hazard. Consider multiple insulation barrier(s) where high voltages are present. Physical Design of Pack and Module for Safety Perhaps the most important aspect of the safe Li-Ion battery pack design is the BMS. Sometimes called the “pack protect circuit” or “safety circuits” in their earlier, less comprehensive instantiations, the BMS is the management brain of the pack that manages it within acceptable performance and safe operating conditions. These circuits have been improved over time to allow an almost unlimited number of series cell connections for high voltage, modular Li-Ion battery systems. Following are the Battery Management System (BMS) Design For Safety typical safety requirements and capability of these systems. • Cell Voltage Safety: The BMS should have a means to prevent any cell in the battery system from being charged or discharged if its cell voltage exceeds a safety threshold. High and low voltage safety thresholds should be set (lowered or raised) with respect to cell temperature. • Cell Current Safety: The BMS should have a means to prevent excessive charge or discharge current through any cell in the battery system. Short circuit currents and extended length high current should be differentiated from expected high pulse currents (i.e., regenerative braking current). Fuses should be considered as a back-up to electronically controlled switches. If multiple cells are hard wired in parallel, fusible links should be considered to limit current flowing into a severely internally shorted cell. • Cell Temperature Safety: The BMS should prevent charge and/or discharge current when the cell temperature is above a dangerous threshold to prevent initiation of thermal run away. The BMS should prevent charge current when the cell temperature is below a low temperature threshold to prevent the immediate creation of Lithium dendrites on the anode. • Cell Balancing: Every non defective cell in the battery system should be balanced to the same relative capacity with the other non defective cells. If the battery system is constructed from series and parallel connected battery modules, a means SouthWest Electronic Energy Group continued on page 18 www.BatteryPowerOnline.com November/December • Battery Power 17 http://www.zigbeeresourceguide.com http://www.zigbeeresourceguide.com http://www.BatteryPowerOnline.com

Table of Contents for the Digital Edition of Battery Power - November 2011

Battery Power - November/December 2011
Contents
Vishay Intertechnology Introduces Powdered-Iron- Based Rx Coil for Wireless Charging
GenSet Eliminator, Designed to Reduce Fuel Consumption and Promote Safety.
The Challenges of Manufacturing Lithium-Ion Batteries for the Electric Vehicle Industry
Considerations for Customized Battery Packs
Efficient Power Protection Means Less Cost, Not Less Reliability
Safety and Preventing Thermal Run Away in Large Li-Ion Batteries
ZigBee Resource Guide
Batteries
Charging & Testing
ICs and Semiconductors
Components
Power Supplies
Industry News
Research & Development
Marketplace
Calendar of Events

Battery Power - November 2011