This project presents a smart, adjustable lithium battery charger designed for 1S, 2S, and 3S (3.7 V – 11.1 V) battery packs, featuring an automatic cut-off mechanism to protect cells from overcharging. The design focuses on simplicity, reliability, and flexibility, making it suitable for DIY energy systems, power tools, backup batteries, and experimental electronics.

At the heart of the circuit is the TL431 precision reference, which continuously monitors the battery voltage through an adjustable resistor network. Using a potentiometer, the cut-off threshold can be finely tuned to match the required full-charge voltage for different battery configurations. Once the battery reaches the preset voltage, the control section triggers a clean shutdown of the charging path.

High-current handling is achieved using IRFZ44N power MOSFETs, allowing the charger to support substantial charging currents while maintaining low losses. These MOSFETs act as electronic switches, automatically disconnecting the charger when the battery is full and reconnecting it when charging is required again. This eliminates the need for manual intervention and significantly improves battery safety and lifespan.

The design also includes clear charging and full-charge LED indicators, giving instant visual feedback on the charging status. Dedicated START and STOP push buttons provide manual control when needed, making the charger practical for both bench use and embedded applications. A robust diode on the input side ensures reverse-polarity protection and prevents unwanted current flow.

This charger is especially useful for makers who want a non-microcontroller-based solution that is easy to understand, adjust, and repair. With commonly available components and a straightforward schematic, it serves both as a functional charging module and an excellent learning project for analog power electronics.

Overall, this Smart 3.7 V Auto Cut-Off Battery Charger delivers a balanced combination of safety, adjustability, and power capability, making it a dependable choice for multi-cell lithium battery charging in DIY and educational projects.

Credit & Acknowledgement

Complete Design & Engineering Credit: Creative Techos (This project is shared for educational and community reference purposes)