BMS also known as Battery Management system (some time PCM – Protection Circuit Module) is essential part of battery pack specially for Lithium Ion and Lithium Ferro Phosphate battery chemistry. There are multiple roles of a BMS in a pack. BMS keeps the cells within permissible voltage levels. This apply to individual and over all pack voltage. Thus BMS doesn’t allow the battery to be charged above upper cutoff voltage and discharge below lower cutoff voltage. BMS also protects the battery from over current and short circuit. Advance BMS have onboard microcontroller and charge control module. Charge control module is capable of keeping the cell voltages balanced either by active or passive balancing. Such BMS often have onboard NTC (one or multiple) for monitoring the battery pack voltage and avoiding any over heat scenario.
So in nutshell, BMS does (some may not have all features) –
- Overcharging Protection
- Deep Discharging Protection
- Over Load Protection
- Short Circuit Protection
- Individual Cell Voltage Monitoring
- Individual Cell Voltage Balancing
- Thermal Protection Again Thermal Runway
- CAN /UART Based Communication
Common Misconception
It is very common misconception that BMS provides constant current for charging. BMS can only limit the upper current and if current is beyond its setting, it would shutdown the battery. In order to achieve the constant current profile, a suitable charger (mostly with CC-CV) should be selected.
| Supported Chemisty | Li-Ion |
|---|---|
| Cells in Series | 7S |
| Nominal Votlage | 25.9V |
| Continuous Discharge Rating | 20Amp |
| Peak Discharge Rating | 30Amp |
| Charge Current | 15Amp |
| Upper Cutoff Voltage | 29.4 ±0.05V |
| Lower Cutoff Voltage | 19.95±0.05V |
| NTC Available | YES |
| Individual Voltage Monitoring | YES |
| Balancing Current | Passive Balancing |
| IP Rating | IP67 (Water Proof) |
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