A Battery Management System (BMS) is any electronic device that manages a rechargeable battery (cell or battery pack), such as by monitoring its state, calculating secondary data, reporting those data, protecting it, controlling its environment, and / or balancing it.

A BMS may monitor the state of the battery as represented by various items, such as:

• Voltage: total voltage, voltage of periodic taps, or voltages of individual cells;
• Temperature: average temperature, air intake temperature, air output temperature, or temperatures of individual cells;
• State Of Charge (SOC) or Depth Of Discharge (DOD): to indicate the charge level of the battery;
• State Of Health (SOH), a variously-defined measurement of the overall condition of the battery;
• Air flow: for air cooled batteries;
• Current: current in or out of the battery.

Additionally, a BMS may calculate values based on the above items. A BMS may report all the above data to an external device, using communication links. A BMS may protect its battery by preventing it from operating outside its safe operating area. The BMS may prevent operation outside the battery's safe operating area. In order to maximize the battery's capacity, and to prevent localized under-charging or over-charging, the BMS may actively ensure that all the cells that compose the battery are kept at the same State Of Charge.

BMS technology range in complexity and performance:

• Simple passive regulators across cells bypass charging current when their cell's voltage reached a certain level, to achieve balancing
• Active regulators intelligently turn on a load when appropriate, again to achieve balancing
• A full BMS reports the state of the battery to a display, and protects the battery

BMS topologies mostly 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: few controllers, each handing a certain number of cells, communicate with each other

Centralized BMSs are most economical, least expandable, and are plagued by a multitude of wires (spaghetti) 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.

Source: Wikipedia.org: Battery Management System

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