Open Battery Charger

Open Battery Smart Charger

Smart 2S Li-Ion battery charger designed in KiCad featuring input protection, power-path management, and intelligent charging control.

Overview

This project implements an intelligent battery charging system for 2-cell Li-Ion batteries (8.4V) with integrated protection and automatic power switching.

The system combines:

• Smart charging control
• Input overvoltage and overcurrent protection
• Automatic source/battery switching
• Auxiliary regulated 3.3V rail
• Battery monitoring interfaces

The design was developed in KiCad 10 as part of a hardware/electronics engineering portfolio project.

Features

• 2S Li-Ion battery charging (8.4V)
• Constant-current / constant-voltage (CC/CV) charging
• Input surge and fault protection
• Power-path management between external supply and battery
• Reverse current protection
• 3.3V regulated output for embedded systems
• Thermistor input for battery temperature supervision
• System and battery voltage interfaces

System Architecture

1. Input Protection Stage

The input stage is protected using the TPS26600 eFuse, providing:

• Overvoltage protection (OVP)
• Current limiting
• Fault protection
• Hot-plug robustness

This stage protects downstream electronics from abnormal supply conditions.

2. Smart Battery Charger

Battery charging is managed using the LT3650, configured for:

• 2S Li-Ion battery charging
• Constant-current / constant-voltage charging profile
• Battery temperature monitoring
• Charging status feedback

3. Power Path Management

The LTC4412 controller enables automatic switching between:

• External DC power source
• Battery supply

This ensures uninterrupted system operation while preventing reverse current paths.

4. Auxiliary Power Rail

A dedicated 3.3V LDO regulator powers low-voltage logic and embedded systems.

Main Components

Specifications

Repository Structure

Open_Battery_Charger/
│
├── hardware/
│   ├── Open_Battery_Charger.kicad_pro
│   ├── Open_Battery_Charger.kicad_sch
│   ├── Open_Battery_Charger.kicad_pcb
│   └── fp-lib-table
│
├── docs/
│   ├── schematic.pdf
│   ├── schematic.png
│   ├── 2D_pcb_top.png
│   ├── 2D_pcb_bottom.png
│   ├── 3D_pcb_top.png
│   ├── 3D_pcb_bottom.png
│   ├── Detailed_Design_Procedure_LT3650.pdf
│   ├── Detailed_Design_Procedure_TPS2660
│   └── Open_Source_Battery_Smart_Charger_Specifications.pdf
│
└── production/
    ├── gerbers/
    └── bom.csv

Schematic

PCB Design

Top View

3D Render

Design Considerations

Key engineering decisions considered during development:

• Input fault protection for safer operation
• Efficient battery charging profile implementation
• Automatic power source switching
• Low-voltage regulation for embedded systems
• Modular architecture for maintainability

Tools

• KiCad 10
• Datasheet-driven design methodology
• Electronic circuit validation

Future Improvements

• PCB manufacturing and validation
• Thermal characterization
• Charging efficiency measurements
• Test reports and oscilloscope captures
• Firmware integration for battery monitoring

License

This project is released under the MIT License.