Acronym · Automotive
BMS (Battery Management System)
The electronics that supervise a traction battery, measuring cell voltages, currents and temperatures, estimating state of charge and health, balancing cells, enforcing safe operating limits and controlling the contactors.
- Also known as
- Battery management
- Type
- Acronym
- Domain
- Automotive, Power and body electronics
Notes
A safety-critical ASIL C or D item, since a mismanaged lithium pack can enter thermal runaway.
Overview
A BMS (battery management system) is the electronics that watches over a rechargeable battery pack, measuring every cell and keeping the pack within safe limits while getting the most usable energy from it. In an electric vehicle it decides how much power can be drawn or accepted, keeps cells in balance and opens the high-voltage contactors when something goes wrong. Smaller versions protect batteries in power tools, laptops, e-bikes and energy storage systems.
How it works
A traction battery is made of many lithium-ion cells in series, and the pack is only as good as its weakest cell. Cell monitoring chips, often called analogue front ends, sit on the modules and measure each cell's voltage and temperature with high accuracy. A pack monitor measures pack voltage and current, and synchronising those readings lets the controller estimate state of charge and state of health. A battery management unit runs the estimation and protection software and talks to the rest of the vehicle.
Cells drift apart over time because of small differences in capacity, self-discharge, impedance and temperature. Balancing corrects this. Passive balancing bleeds energy from the fullest cells through a resistor switched by a transistor, which is simple and cheap but wastes energy as heat. Active balancing moves charge between cells with capacitors or inductive circuits, which is more efficient but needs more components.
The BMS also enforces safety. It drives the contactors that connect the pack to the vehicle, handles pre-charge, monitors isolation between the high-voltage system and the chassis, and supports fast disconnection, sometimes with a pyrotechnic fuse. Because a lithium-ion cell outside its safe operating area can overheat or catch fire, automotive BMS chipsets are developed with ISO 26262 support, often up to ASIL D. Newer designs replace the wired daisy chain between modules with a wireless link.
Examples
- A cell monitoring chip measuring a stack of series cells and switching internal bleed resistors to balance them.
- A pack monitor that measures current, pack voltage and insulation resistance in a high-voltage vehicle battery.
- A wireless BMS that replaces the wired link between battery modules with an automotive-qualified radio microcontroller.
- A contactor driver and pyro-fuse driver used to disconnect the high-voltage battery quickly after a fault.
Why it matters
The BMS sets how much of a battery's capacity can be used safely, so it directly affects driving range, charging speed, battery life and safety. Battery management IC designers, automotive ECU hardware engineers, functional safety teams and firmware developers work on it, and it is a large market for analogue, mixed-signal and isolation chips.
Related terms
Part of the Automotive glossary, with every term in the topic and the lifecycles, tools and standards that use them.
Where it appears on the Hub
Used on 6 pages of the Hub. In each group, the pages that mention it most come first.
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Last reviewed . Written by The Semiconductor Hub editorial team. The full glossary