This repository contains the hardware design files (Altium Designer) and documentation for a custom Smart BMS designed for 4S Li-ion battery packs. The system features a hybrid architecture using STM32G4 for critical protection logic and ESP32 for wireless telemetry.
This project aims to create a robust, educational-grade Battery Management System capable of monitoring, balancing, and protecting a 4S configuration (16.8V max). Unlike standard analog BMS boards, this "Smart" design separates the Analog Front End (AFE) from the Control Logic, allowing for advanced SoC/SoH algorithms, data logging, and remote monitoring via Wi-Fi/BLE.
- Hybrid Control Architecture:
- AFE: TI BQ76920 for precise voltage/current measurement and hardware protection.
- MCU: STM32G431CBT6 for running Kalman Filter based SoC algorithms and system management.
- Telemetry: ESP32-WROOM-32 for Wi-Fi/Bluetooth connectivity (IoT Dashboard ready).
- Power Stage: High-current path with 6x Back-to-Back MOSFETs and Low-Side Current Sensing (1mΩ Shunt).
- Communication: Integrated CAN FD Transceiver (MCP2562) and USB-UART (CH340E) for debugging.
- Data Logging: Onboard W25Q128 External Flash for storing error logs and historical battery data.
| Feature | Description |
|---|---|
| Battery Configuration | 4S Li-ion (Nominal 14.4V, Max 16.8V) |
| Continuous Discharge | ~30A |
| Peak Discharge Current | ~50-60A |
| Microcontroller | STM32G431CBT6 (Cortex-M4) |
| Analog Front End (AFE) | TI BQ76920 (I2C Interface) |
| Wireless Module | ESP32-WROOM-32 (Wi-Fi + BLE) |
| Current Sensing | Low-Side Measurement (1mΩ Shunt Resistor) |
| Regulators | TPS5430 (5V Buck) & AMS1117 (3.3V LDO) |
| Communication | CAN Bus, USB (Serial), UART, SWD |
The system connects between the 4S Battery Pack and the Load/Charger.
- Power & Protection Stage: The BQ76920 constantly monitors cell voltages and current via the shunt resistor. It drives the High-Side Charge/Discharge MOSFETs directly.
- Control Stage (STM32): Reads data from the AFE via I2C, calculates State of Charge (SoC), manages passive balancing, and handles CAN bus communication.
- Connectivity Stage (ESP32): Receives data from the STM32 via UART and pushes it to a web interface or mobile app.
- Educational Project: This PCB was designed as part of an advanced engineering learning process to practice Altium Designer and Embedded Systems concepts.
- Thermal Management: For continuous high-current applications (>30A), additional cooling (heatsink) on the MOSFETs and enhanced airflow is recommended.
- Safety: Always test with a current-limited power supply before connecting actual lithium cells.
- U1 (AFE): BQ7692000PWR
- Uxxx (MCU): STM32G431CBT6
- Wireless: ESP32-WROOM-32
- MOSFETs: N-Channel Power MOSFETs (Back-to-Back config)
- Flash: W25Q128JV (SPI)
- CAN Tx: MCP2562-H/SN
- Buck Converter: TPS5430DDA
- Shunt: 1mΩ High Power Resistor
This project is open-source and available under the MIT License.