Description
4S 40A BMS for 4-Cell Lithium Battery Packs
This BMS module for four cells in series (4S) supports continuous discharge current up to 40 A and protects a 14.8 V Li-ion pack (maximum charge voltage listed as 16.8–18.1 V). It includes passive cell balancing to help extend battery life.
🔧 Technical specifications
- Configuration: 4 cells in series (3.6 V / 3.7 V nominal; 16.8 V maximum charge)
- Continuous discharge current: 40 A (up to 60 A peak with suitable cooling)
- Maximum charge current: 20 A continuous (adjustable depending on version)
- Balancing current: approx. 100 mA per cell
- MOSFETs: 10 low-resistance transistors to limit losses
- Recommended charging voltage: 16.8–18.1 V (4 × 4.2 V)
- Built-in protection: overcharge (OVP), over-discharge (UVP), overcurrent (OCP), short circuit, reverse polarity, and over-temperature
- PCB dimensions: approx. 55 × 45 × 3.4 mm
- Operating temperature: −20 °C to +60 °C
💡 Typical applications
- Li-ion packs for e-bikes, electric scooters, and cordless tools
- Drones and RC models requiring high current
- Test benches and portable power supplies
- UPS systems and DIY power banks
- Arduino/ESP32 projects powered by a 14.8 V pack
🛠️ Connections / pinout
| Pin | Description |
|---|---|
| B– | Pack negative (cell 1 negative) |
| B1 | Junction between cell 1 and cell 2 |
| B2 | Junction between cell 2 and cell 3 |
| B3 | Junction between cell 3 and cell 4 |
| B+ | Pack positive (cell 4 positive) |
| P– | Negative output to charger or load (usually connected to B–) |
| P+ | Positive output to charger or load (usually connected to B+) |
Connect the pack wires in this order: B– → B1 → B2 → B3 → B+. Then connect P– / P+ to the load or charger. Always check polarity and insulation during installation.
