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ITGlossary · Batteries
Battery Management System (BMS)
A system that monitors and manages the performance, health, and charging of batteries.
Technical level:Intermediate
A battery management system continuously measures each cell's voltage, the current and the temperature, calculates the state of charge (SoC) and state of health (SoH), and balances the cells against each other. If anything goes out of limits, such as overcharge, deep discharge, overcurrent or extreme temperature, it disconnects the battery to protect it.
In lithium batteries, such as the LiFePO4 types used in solar systems and UPS units, a BMS is essential for safe operation. Through a communication link, usually CAN or RS485, it tells the inverter or UPS how much current the battery can accept or deliver.
A common mistake is pairing a battery and an inverter without checking that they support a common communication protocol. Without it, the system runs with limitations or not at all.
Related terms
- Battery Charging CurrentThe amount of current supplied to charge a battery, regulated by the UPS system.
- Equalising ChargeA controlled charge at a higher than normal voltage that brings all cells of a lead-acid battery to the same state of charge.
- Fast ChargingA charging method that restores battery capacity quickly without damage by controlling current, voltage and temperature.
- VRLA BatteryA sealed, valve-regulated lead-acid battery that never needs topping up with water and is used in most UPS systems.
- C-rateThe charge or discharge current expressed as a multiple of battery capacity, e.g. 1C for a 100 Ah battery means 100 A.
- Cycle LifeThe number of charge and discharge cycles a battery withstands until its capacity falls, usually, to 80% of the original.