Vector BMS

Open-source Battery Management System designed for high-voltage lithium battery packs with VESC integration.

Overview

Vector BMS is a modular BMS supporting up to 24 series cells (24S) with:

• Active cell monitoring and balancing
• High-current sensing (up to 120A)
• CAN bus communication (VESC-compatible)
• USB interface for configuration
• Isolated design for safety

Firmware: This project uses VESC BMS firmware for full VESC Tool integration.

Hardware Architecture

Schematic Structure

Vector_BMS.kicad_sch (Main)
├── Power management
├── Cell monitoring (LTC6811 × 2)
├── Current sensing (INA226)
├── High-side switching
└── Connectors

MCU.kicad_sch
├── STM32L476 microcontroller
├── CAN interface (isolated via ISO1050)
├── isoSPI interface (LTC6820)
└── USB interface (CP2104)

cell.kicad_sch / cell2.kicad_sch
└── Per-cell balancing circuits (×12 each)

Key Components

Component	Part Number	Function
MCU	STM32L476RGT6	ARM Cortex-M4, 80MHz, low power
Cell Monitor	LTC6811-1 (×2)	12-cell stack monitor, ±1.2mV accuracy
isoSPI	LTC6820	Isolated SPI for LTC6811 daisy chain
Current Sensor	INA226	16-bit I2C power monitor
Shunt Resistor	WSLP5931L1000FEA	0.1mΩ, 15W, ±1%
CAN Transceiver	ISO1050DUBR	Isolated CAN 2.0B
USB-UART	CP2104	USB to UART bridge
DC-DC	LM5165	Wide-input buck converter
Balance FET	DMG2305UX-7	P-ch MOSFET, SOT-23
Balance Resistor	CRCW25123R90JNEA	3.9Ω, 1W, 2512
High-side Switch	IRFL4105PBF	N-ch logic-level MOSFET

Cell Configuration

• Maximum cells: 24S (two LTC6811 in daisy chain)
• Cell voltage range: 0V to 5V per cell (compatible with most Li-ion/LiFePO4)
• Balance current: ~1A per cell @ 4.2V (passive balancing via 3.9Ω resistor)
• Temperature monitoring: 3× NTC thermistors

Current Sensing

• Shunt: 0.1mΩ (WSLP5931, 15×7.6mm)
• Max continuous: 120A
• Sensor: INA226 (16-bit I2C power monitor)
• Resolution: ~1mA per LSB
• Power dissipation: 1.44W at 120A

VESC BMS Firmware

Vector BMS uses the VESC BMS firmware which provides:

• ✅ Cell monitoring and balancing
• ✅ Charge control with CC/CV support
• ✅ Low-power sleep mode
• ✅ CAN-bus integration with VESC motor controllers
• ✅ USB configuration via VESC Tool
• ✅ Ah and Wh counting
• ✅ Distributed balancing across multiple BMSes
• ✅ Bootloader and firmware update support

Building Firmware

Prerequisites

1. ARM GCC Toolchain

   # Ubuntu/Debian
   sudo apt install gcc-arm-none-eabi
   
   # macOS
   brew install arm-none-eabi-gcc
   
   # Windows: Download from ARM website

2. ChibiOS (included as submodule in VESC BMS)

3. Make

Clone and Build

# Clone VESC BMS firmware
git clone --recursive https://github.com/vedderb/vesc_bms_fw.git
cd vesc_bms_fw

# Copy Vector BMS hardware config
cp /path/to/Vector-BMS/firmware/vesc_bms_hw/hw_vector_bms.h hwconf/
cp /path/to/Vector-BMS/firmware/vesc_bms_hw/hw_vector_bms.c hwconf/

# Build for Vector BMS
make HWCONF=hw_vector_bms

# Output: build/vesc_bms_fw.bin

Flashing

Using ST-Link:

# Flash via OpenOCD
openocd -f interface/stlink.cfg -f target/stm32l4x.cfg \
    -c "program build/vesc_bms_fw.bin 0x08000000 verify reset exit"

# Or via st-flash
st-flash write build/vesc_bms_fw.bin 0x08000000

Using VESC Tool (for updates):

1. Connect Vector BMS via USB
2. Open VESC Tool
3. Go to Firmware → Bootloader
4. Select vesc_bms_fw.bin and upload

Hardware Configuration

The Vector BMS hardware config is in firmware/vesc_bms_hw/:

firmware/vesc_bms_hw/
├── hw_vector_bms.h     # Pin definitions, parameters
└── hw_vector_bms.c     # Initialization, INA226 driver

Key parameters in hw_vector_bms.h:

#define HW_CELLS_SERIES         24          // Cell count
#define HW_SHUNT_RES            (0.1e-3)    // Shunt resistance
#define HW_INA226_I2C_ADDR      0x40        // INA226 address

VESC Tool Configuration

1. Connect Vector BMS via USB
2. Open VESC Tool and connect
3. Go to VESC BMS tab
4. Configure:
   • Cell count: 24
   • Balance start voltage
   • Balance delta voltage
   • Current limits
   • Temperature limits
5. Write Configuration

MCU Pin Mapping

Function	STM32 Pin	Notes
SPI1_NSS (LTC6820)	PA4	Directly driven CS
SPI1_SCK	PA5	isoSPI clock
SPI1_MISO	PA6	isoSPI data in
SPI1_MOSI	PA7	isoSPI data out
I2C1_SDA (INA226)	PB7	Current sensor
I2C1_SCL	PB6	Current sensor
CAN1_RX	PB8	Via ISO1050
CAN1_TX	PB9	Via ISO1050
USART1_TX	PA9	Via CP2104 to USB
USART1_RX	PA10	Via CP2104 to USB
CHG_EN	PC6	Charge enable
DSG_EN	PC7	Discharge enable
PCHG_EN	PC8	Precharge enable
LED_RED	PA0	Status LED
LED_GREEN	PA1	Power LED
BUZZER	PA8	Audible alarm

Connectors

Connector	Function
J1	Main battery input
J2	Charger input
J3	OLED display (I2C)
J12	CAN bus
J14	Serial/debug
J17	Power button
J24	USB (CP2104)

Hardware Design

Prerequisites

• KiCad 9.0+ for schematic/PCB editing

Opening the Project

1. Clone the repository
2. Open Vector_BMS.kicad_pro in KiCad
3. Review schematic and PCB layout
4. Generate BOM and fabrication files

License

Hardware: Open Source (license TBD) Firmware: GNU GPL v3 (VESC BMS)

Contributing

Contributions welcome! Please open an issue or pull request.

Acknowledgments

• Benjamin Vedder for VESC BMS firmware
• VESC Project for the open-source motor controller ecosystem
• Analog Devices for LTC6811 reference designs
• Arrow DAO community