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Electric vehicles (EVs) and hybrid electric vehicles (HEVs) are using lithium batteries consisting of multiple of cells. The battery cells are placed in series to create high voltage capability; in parallel to enable higher currents — creating an elaborate matrix of cells. (An electric vehicle like the Tesla Roadster will absorb more than 900 amperes on acceleration. What Tesla promotes as its “secret sauce” is its battery technology — 300 miles on a single recharge).
On a multi-cell battery, the variables like voltages, currents, temperatures, and the number of charging cycles (aging factors) are carefully monitored when the battery is charged, and discharged in use. If one cell draws more current on charging than its neighbors, you have the possibility of a hot spot in the serial or parallel cell string. If it draws significantly less current than its neighbors, you have the possibility of developing a dead cell ? and that threatens the life of the entire string. For these applications, the durability of the battery is assessed by monitoring each cell. A multi-cell monitoring IC lie Linear Technology Corp.’s LTC6811 measures separate cell voltages up to 5V, in a multiplexed sequence, with a total measurement error of less than 1.2mV. All 12 cells can be measured in 290µs.