Feature: Energy storage
Battery internals
changes non-linearly during discharge, determining remaining capacity requires complex modelling of the discharge curve. Dedicated fuel-gauge devices handle this calculation and report the remaining charge level to the system or user interface. Power flow into and out of the battery pack is typically
controlled using back-to-back MOSFETs, which allow the system to independently enable or disable charging and discharging paths. In higher-voltage systems, larger contactor relays may be used instead. Together, these components create a layered control system
capable of monitoring cell health and preventing unsafe operating conditions.
Cell balancing and pack stability When cells are connected in a series, maintaining balance between them becomes one of the most important tasks of the BMS. Cells rarely behave identically over time. Small variations in
CEI battery pack
manufacturing or usage conditions can cause one cell to charge or discharge slightly faster than another. Over repeated cycles, these differences accumulate. If a single cell reaches the upper voltage limit while others remain
partially charged, the pack can’t continue charging without risking damage to that cell. Conversely, a weak cell may reach its discharge limit early, reducing the usable capacity of the entire battery pack. Balancing circuits address this problem. Two primary approaches are used: passive balancing and active balancing. Passive balancing dissipates excess energy from higher-voltage
cells through resistors, releasing it as heat until all cells equalise. Although energy is lost in this process, passive balancing is widely used because it is relatively simple and inexpensive to implement. By contrast, active balancing transfers energy from higher voltage
cells to lower voltage cells. While more efficient, this method requires additional circuitry and complexity. In many lithium-ion systems, balancing begins when cell voltages
Linking two CMP2500 battery systems 40 May 2026
www.electronicsworld.co.uk
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