A Battery Management System (BMS) prevents overcharging and over-discharging of batteries primarily through real-time monitoring, control, and protective mechanisms focused on each individual cell within the battery pack.
How a BMS Prevents Overcharging
- Voltage Monitoring: The BMS continuously monitors the voltage of each cell or string in the battery pack. When any cell approaches its maximum safe voltage limit (typically around 3.75 V per cell for lithium-ion), the BMS takes action to avoid further voltage increase that could lead to overcharging and potential damage.
- Cutting Off Charging Current: Upon detecting a cell reaching the overcharge threshold, the BMS cuts off or limits the charging current to stop the charging process. This prevents the voltage from rising beyond a safe point.
- Cell Balancing: The BMS actively balances the charge across all cells by shunting excess charge from cells that are near full charge to those with lower charge levels. This balancing can be done passively by dissipating excess energy through resistors or actively by redistributing charge, ensuring no individual cell is overcharged while others lag behind.
How a BMS Prevents Over-Discharging
- Voltage Threshold Monitoring: The BMS monitors the voltage during discharge and prevents any cell from dropping below a critical minimum voltage that could cause irreversible damage or reduce battery life.
- Discharge Cutoff: When the voltage of any cell or the pack reaches the low-voltage cutoff point, the BMS stops further discharge by disconnecting the load or alerting the system. This prevents deep discharge scenarios that degrade battery health.
Additional Protective Functions Supporting Overcharge/Over-Discharge Prevention
- Temperature Monitoring: The BMS includes temperature sensors (like NTC thermistors) to track battery temperature. If cells get too hot during charging or discharging, the BMS can reduce charging rates or halt operations to prevent thermal damage, which could otherwise worsen the effects of overcharge or over-discharge.
- Current and Short Circuit Protection: Besides voltage and temperature, a BMS also monitors current flow to prevent overcurrent and short circuits, which could exacerbate risks during charging or discharging.
In summary, the BMS acts as a sophisticated control system that constantly monitors cell voltages, temperature, and current, and dynamically manages charging/discharging processes to keep all cells within their safe operating limits. This includes stopping charge when cells reach their safe maximum, stopping discharge before cells go too low, and balancing cells to prevent uneven stress—thereby protecting the battery pack from overcharge and over-discharge damage and extending its lifespan.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-a-bms-prevent-overcharging-and-over-discharging/
