page_title: Battery management system
section_title: Topologies
hierarchical_section_title: Battery management system / Topologies
caption_attribution_description: English: BMS Wireless Communication
context_page_description: A battery management system is any electronic system that manages a rechargeable battery, such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and / or balancing it.
  A battery pack built together with a battery management system with an external communication data bus is a smart battery pack. A smart battery pack must be charged by a smart battery charger.
context_section_description: BMS technology varies in complexity and performance:
  Simple passive regulators achieve balancing across batteries or cells by bypassing charging current when the cell's voltage reaches a certain level. The cell voltage is a poor indicator of the cell's SOC (and for certain Lithium chemistries such as LiFePO4 it is no indicator at all), thus, making cell voltages equal using passive regulators does not balance SOC, which is the goal of a BMS. Therefore, such devices, while certainly beneficial, have severe limitations in their effectiveness.
  Active regulators intelligently turning on and off a load when appropriate, again to achieve balancing. If only the cell voltage is used as a parameter to enable the active regulators, the same constraints noted above for passive regulators apply.
  A complete BMS also reports the state of the battery to a display, and protects the battery.
  BMS topologies fall in 3 categories:
  Centralized: a single controller is connected to the battery cells through a multitude of wires
  Distributed: a BMS board is installed at each cell, with just a single communication cable between the battery and a controller
  Modular: a few controllers, each handing a certain number of cells, with communication between the controllers
  Centralized BMSs are most economical, least expandable, and are plagued by a multitude of wires.
  Distributed BMSs are the most expensive, simplest to install, and offer the cleanest assembly.
  Modular BMSs offer a compromise of the features and problems of the other two topologies.
  The requirements for a BMS in mobile applications (such as electric vehicles) and stationary applications (like stand-by UPSs in a server room) are quite different, especially from the space and weight constraint requirements, so the hardware and software implementations must be tailored to the specific use. In the case of electric or hybrid vehicles, the BMS is only a subsystem and cannot work as a standalone device. It must communicate with at least a charger (or charging infrastructure), a load, thermal management and emergency shutdown subsystems. Therefore, in a good vehicle design the BMS is tightly integrated with those subsystems. Some small mobile applications (such as medical equipment carts, motorized wheelchairs, scooters, and fork lifts) often have external charging hardware, however the on-board BMS must still have tight design integration with the external charger.
  Various Battery balancing methods are in use, some of them based on state of charge theory.
caption: BMS Wireless Communication
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