Hardware Design for Tesla Model 3/Y Battery Management System

This repository contains the KiCad PCB design files for a replacement Battery Management System (BMS) designed for Tesla Model 3 and Model Y battery packs. This hardware interfaces with high-voltage (400V) battery modules using the isoSPI protocol and provides comprehensive monitoring, control, and safety features.

🔗 Companion Firmware Repository: isoSPI-M3Y-BMS

This PCB design implements a complete BMS controller capable of:

• Direct BMB Communication: isoSPI master interface for Battery Management Boards
• High Precision Monitoring: Current, voltage, temperature, and power measurement
• CAN Bus Integration: 500kbps communication with vehicle systems and inverters
• Contactor Control: Safe sequenced activation of high-voltage contactors
• Cell Balancing: Individual cell balancing control through BMB modules
• Safety Features: Overcurrent, overvoltage, undervoltage, and thermal protection

Tesla Model 3 and Model Y battery packs utilize a modular architecture:

• Cell Configuration: 4416 cells (96s46p) in 4 modules
• Module Configuration: 24 cells in series per module (96 total series groups)
• Nominal Voltage: ~350V (fully charged: ~400V, discharged: ~280V)
• Capacity: Varies by pack (50-82 kWh depending on model/year)
• Battery Management Boards (BMBs): Each module contains BMBs that monitor cell groups
• Communication: Original packs use proprietary Tesla BMS; this project replaces it

Why Replace the BMS?

• Reuse Tesla packs in DIY electric vehicle conversions
• Second-life energy storage systems
• Research and educational purposes
• Open-source alternative to proprietary systems

isoSPI-M3Y-BMS-PCB/
├── isoSPI-M3Y-BMS-PCB.kicad_pro    # KiCad project file
├── isoSPI-M3Y-BMS-PCB.kicad_sch    # Main schematic design
├── isoSPI-M3Y-BMS-PCB.kicad_pcb    # PCB layout
├── BMS_Library/                     # Custom component library
│   ├── BMS_Library.kicad_sym        # Symbol library
│   └── BMS_Library.pretty/          # Footprint library
├── RP2350_KiCad/                    # RP2350 MCU resources
│   ├── RP2350A_QFN-60*.kicad_mod    # Footprints
│   ├── RP2350A-QFN60.step           # 3D model
│   └── rp2350a-qfn60.kicad_sym      # Symbol
├── bms.3dshapes/                    # 3D models for connectors
├── reassociate_components.py        # Component re-linking utility
├── apply_mapping.py                 # Reference mapping tool
└── fabrication-toolkit-options.json # Manufacturing outputs config

• KiCad 8.0+ - Download here
• Python 3.7+ (for utility scripts)
• Basic understanding of PCB design and high-voltage safety

1. Clone the repository:

   git clone https://github.com/clowrey/isoSPI-M3Y-BMS-PCB.git
   cd isoSPI-M3Y-BMS-PCB

2. Open in KiCad:

   • Launch KiCad
   • Open isoSPI-M3Y-BMS-PCB.kicad_pro

3. Library Configuration:

   • Libraries are configured in local sym-lib-table and fp-lib-table
   • Project-specific libraries (BMS_Library, RP2350_KiCad) should load automatically
   • If missing components appear, verify library paths in KiCad preferences

• Schematic: Open isoSPI-M3Y-BMS-PCB.kicad_sch to view circuit design
• PCB Layout: Open isoSPI-M3Y-BMS-PCB.kicad_pcb to view board layout
• 3D View: Press Alt+3 in PCB editor to visualize the assembled board

• 12V input with protection and filtering
• 3.3V LDO for MCU and logic
• Isolated power for isoSPI interface

• QFN-60 package with thermal pad
• Crystal oscillator for precision timing
• JTAG/SWD debug interface
• Boot mode selection

• Shunt resistor-based measurement
• 20-bit delta-sigma ADC
• Bidirectional current monitoring
• I2C interface to MCU

• 4-channel pack voltage measurement
• Precision resistor dividers (high voltage to ADC range)
• Individual cell voltages via isoSPI
• 12-bit internal ADC

• Differential transformer coupling
• Manchester encoding via PIO
• Galvanic isolation from high voltage
• Master and snooper mode support

• Hardware CAN transceiver
• 120Ω termination (configurable)
• PIO-based CAN 2.0B implementation
• 500kbps operation

• 4 independent high-current outputs
• PWM inrush current limiting
• Sequenced activation logic
• Flyback protection diodes

• High-voltage battery pack connector
• 12V power input
• CAN bus connector
• USB programming interface
• Debug headers

Re-links PCB footprints to schematic symbols after copying design sections. This is essential when:

• Copying and pasting PCB sections (breaks UUID links)
• Duplicating circuits for multi-channel designs
• Recovering from schematic/PCB desynchronization

Usage:

python reassociate_components.py

The script:

1. Parses both .kicad_sch and .kicad_pcb files
2. Matches components by reference designator and type
3. Updates PCB footprints with correct schematic UUIDs
4. Creates backup before modification

Applies specific component reference remapping (e.g., when renaming U11→U27). Updates both reference designators and UUID linkages.

Usage:

python apply_mapping.py

The project includes fabrication-toolkit-options.json for automated manufacturing output generation.

Recommended manufacturers:

• JLCPCB
• PCBWay
• OSH Park
• Any PCB fab supporting 4+ layer boards

⚠️ CRITICAL SAFETY REQUIREMENTS:

• Clearances: Maintain minimum 4mm creepage distance for 400V
• Isolation: isoSPI and current sensing must maintain galvanic isolation
• Testing: All HV sections require hi-pot testing before energization
• Conformal Coating: Recommended for high-voltage traces
• Certifications: May require UL/CE certification for commercial use

• Most components available from Digi-Key, Mouser, or LCSC
• RP2354B: Available from Raspberry Pi approved distributors
• INA228: Texas Instruments or authorized distributors
• Connectors: Match to Tesla pack interface specifications

1. SMD Components: Reflow solder all surface mount parts
2. Through-hole: Hand solder connectors and large components
3. Inspection: Verify all solder joints and orientation
4. Testing: Low-voltage functional testing before HV connection
5. Programming: Flash firmware via USB or SWD
6. Calibration: ADC and current sensing calibration routines

This PCB is designed to work with the companion firmware:

📦 isoSPI-M3Y-BMS Firmware

Hardware Drivers:

• RP2354B microcontroller with dual Cortex-M33 cores
• INA228 current/voltage/power sensor driver
• Internal ADC for pack voltage monitoring (4 channels)
• Contactor control (4 channels, sequenced activation)
• Serial command processing (30+ commands)
• CAN bus interface (can2040, 500kbps broadcast)
• isoSPI PIO master implementation
• isoSPI passive bus snooper
• Unified BMB test interface
• Runtime interface switching (Batman/isoSPI)

System Features:

• Parameter system with 108+ BMS parameters
• Coulomb counting for SOC tracking
• Automatic 10Hz pack status CAN broadcasting
• Statistics tracking for TX/RX/errors
• Configurable message IDs and data formatting

• BATMan/isoSPI interface switching
• Runtime interface control (automatic disable/enable)
• Full BMS state machine
• Cell voltage reading via isoSPI
• Cell balancing control
• Temperature monitoring

• Hardware testing and validation
• Calibration routines for ADC
• Flash storage for calibration data
• Error handling and recovery
• Extended testing (24+ hours)
• Performance optimization
• Documentation completion

1. Clone the firmware repository
2. Install Pico SDK and build tools (CMake-based)
3. Build the project:

   cd isoSPI-M3Y-BMS
   mkdir build && cd build
   cmake ..
   make

4. Flash to RP2354B via USB or SWD
5. Connect via serial interface (115200 baud)
6. Configure using serial commands
7. Optional: Integrate with ESPHome for monitoring and display

The firmware supports integration with ESPHome for advanced monitoring via touchscreen displays:

ESPHome Features:

• Three-Page Display Interface:
  • Main overview with key parameters
  • Detailed battery information
  • Cell voltage graph (all 108 cells visualized)
• Real-time Monitoring: Live parameter updates every 5-10 seconds
• Touch Controls: Balance on/off, page navigation
• Home Assistant Integration: All BMS parameters as HA entities
• Professional UI: LVGL-based interface optimized for 480x320 displays

Supported Hardware:

• JC4832W535 480x320 QSPI touchscreen
• ESP32-S3 based display modules
• WiFi connectivity for OTA updates

See the ESPHome interface documentation in the firmware repository for setup instructions.

This system interfaces with 400V battery packs that can deliver LETHAL current.

• Only qualified personnel should work on high-voltage systems
• Proper isolation and safety measures required
• Use appropriate personal protection equipment (PPE)
• Follow all electrical safety protocols
• Discharge pack completely before service
• EV battery systems can deliver lethal current
• Follow all lockout/tagout procedures

• This is a development version (v2.0.0)
• isoSPI implementation is experimental
• BATMan protocol partially implemented
• Extensive testing required before production use
• USE AT YOUR OWN RISK
• No warranty expressed or implied
• Not certified for commercial EV use
• User assumes all responsibility for safety

• Insulated high-voltage gloves (Class 00 minimum)
• Safety glasses with side shields
• Insulated tools rated for 1000V
• Multimeter rated for CAT III 600V or higher
• Isolation transformer for bench testing
• Emergency shutdown procedures
• First aid and emergency response plan

• Firmware Repository: isoSPI-M3Y-BMS
• RP2354B Datasheet: Raspberry Pi Documentation
• INA228 Datasheet: Texas Instruments
• Pico SDK: Raspberry Pi Pico SDK
• can2040 Library: Kevin O'Connor's can2040
• Original BATMan BMS: Damien Maguire & Tom de Bree

• Schematic PDF exports (generate from KiCad)
• Bill of Materials (generate from KiCad BOM tool)
• Assembly drawings (generate from KiCad fabrication outputs)
• Test procedures (in firmware repository)
• CAN message format documentation (in firmware repo)
• Calibration procedures (in firmware repo)

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch (git checkout -b feature/improvement)
3. Make your changes with clear commit messages
4. Test thoroughly (especially high-voltage sections)
5. Submit a pull request with detailed description

Areas for contribution:

• Schematic improvements
• PCB layout optimization
• Additional protection circuits
• Manufacturing DFM improvements
• Documentation enhancements
• Test jig designs

This project is licensed under the GNU General Public License v3.0 - see the LICENSE file for details.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

In summary:

• ✅ Free to use, modify, and distribute
• ✅ Must disclose source code
• ✅ Must use same GPL-3.0 license
• ✅ State changes made to original
• ❌ No warranty provided

• Damien Maguire & Tom de Bree - Original BATMan BMS software
• ESPHome Community - Framework and component support
• Kevin O'Connor - can2040 library for RP2040/RP2350
• Raspberry Pi Foundation - Pico SDK and excellent documentation
• Texas Instruments - INA228 current sensing IC
• KiCad Community - Excellent open-source EDA tools
• Analog Devices - isoSPI protocol and reference designs
• Tesla Motors - Battery module architecture reference

• Issues: Use GitHub Issues for bug reports and feature requests
• Discussions: GitHub Discussions for general questions
• Pull Requests: Contributions welcome via GitHub PR

Complete platform migration supporting firmware v2.0.0:

• Microcontroller: Migrated from ESP32 to Raspberry Pi RP2354B

  • Dual Cortex-M33 cores @ 150MHz
  • QFN-60 package with thermal management
  • Native USB support for programming and debugging
  • Hardware SWD debug interface

• Current Sensing: Replaced AS8510 with Texas Instruments INA228

  • 20-bit delta-sigma ADC
  • High-side and low-side sensing capability
  • I2C interface with configurable address
  • Integrated power calculation

• Pack Voltage Monitoring: Added 4-channel internal ADC monitoring

  • Precision voltage dividers for 400V → 3.3V range
  • 12-bit resolution
  • Individual channel filtering

• CAN Bus: Integrated hardware CAN transceiver

  • Native CAN 2.0B support via PIO
  • 500kbps operation
  • Configurable termination (120Ω)

• isoSPI Implementation:

  • Differential transformer coupling with galvanic isolation
  • PIO-based Manchester encoding/decoding
  • Master mode for direct BMB communication
  • Passive snooper mode for bus monitoring
  • Runtime switching between BATMan SPI and isoSPI

• Enhanced Contactor Control:

  • 4-channel PWM drivers with inrush limiting
  • Sequenced activation logic in hardware
  • Flyback protection for inductive loads

• Unified Testing Interface:

  • Single test connector for both BATMan and isoSPI modes
  • Automatic interface detection

This hardware revision requires firmware v2.0.0 or later from the companion repository:

• isoSPI-M3Y-BMS v2.0.0 Changelog

Original ESP32-based design:

• ESP32-WROOM-32 microcontroller
• AS8510 current sensor
• Arduino framework
• BATMan SPI communication only
• ESPHome integration support

Current Hardware Version: v2.0 (RP2354B-based design)

PCB Development Status:

• ✅ Schematic design complete
• ✅ Component selection finalized
• 🔄 PCB layout in progress
• ⏳ Design rule check (DRC) pending
• ⏳ Prototype fabrication pending
• ⏳ Hardware validation pending
• ⏳ Production testing pending

Companion Firmware Status:

• Version: v2.0.0 (November 2025)
• Status: Active development
• Phase: isoSPI implementation in progress (Phase 3)
• See: Firmware Repository for detailed status

• Enhanced thermal management
• Additional redundant safety circuits
• Wireless monitoring interface
• Integrated display option
• Automotive-grade component variants
• Extended temperature range support
• Multi-pack support with CAN bridging
• Production test fixture design

⚡ Building the future of open-source battery management systems ⚡