Feature: Batteries


Figure 1: Measuring the voltage across any single cell of a series string is simple in concept, requiring only a fl oating digital voltmeter


Figure 2: A real-world battery pack is an array of series- and parallel-connected cells in modules, with a signifi cant amount of stored energy; these are factors that greatly complicate the task of measuring cell voltages


• Determining battery pack state-of-charge (SOC) and state-of-health (SOH) in order to provide accurate predictions of remaining capacity (run time) and overall life expectancy.


• Providing the data needed to implement cell balancing, which equalises the voltage of charged cells with respect to each other, despite their internal diff erences, as well as diff erent locations, temperatures and ageing. Failure to perform cell balancing results in reduction in battery pack performance at best, and cell failure at worst. Balancing can be accomplished using passive or active techniques; the latter provide somewhat better results, but are more costly and complex.


• Preventing many conditions that can damage the battery and lead to safety concerns for the user, their vehicle and its occupants. T ese include unwelcome scenarios such as: • Overvoltage or charging at excessive current, which can lead to thermal runaway.


Figure 3: Analog Devices’s MAX17843 12-channel battery-monitoring data-acquisition interface incorporates multiple safety features, making it suitable for automotive applications


• Undervoltage: a single over-discharge won’t cause catastrophic failure, but it may start to dissolve the anode conductor. Subsequent repeated over- discharge cycles can lead to lithium plating in the recharging cell and, again, potentially thermal runaway;


www.electronicsworld.co.uk June 2022 23


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