• Designer: adrian95
• Design Platform: Flux
• Microcontroller: ATtiny841-SSU
• Project version: #a52b4bed
• Original project: https://www.flux.ai/adrian95/bms~q8s

Overview

This project is a compact, do-it-yourself battery management system designed by adrian95 in the browser-based Flux environment. It is built around the ATtiny841-SSU, an 8-bit AVR microcontroller that supervises the pack. The board is engineered to do three things well: balance cells effectively, survive electrical faults, and keep operating reliably when the battery voltage falls.

Design Philosophy

A battery management system faces its hardest conditions at exactly the moments it matters most: a heavily loaded pack, a nearly depleted cell, a noisy supply line. Many hobby-grade boards work on the bench and then struggle in the field. This design addresses that gap with a small number of deliberate choices.

The first is a higher balance current. Cells in a series pack inevitably drift apart, and the faster a BMS can pull them back into agreement, the healthier the pack stays over time. This board is built to give balancing more headroom.

The second is protection. A fuse guards the board against fault and overcurrent conditions, while a TVS diode clamps voltage spikes before they can reach sensitive components. Together they make the hardware far more tolerant of the transients that real power systems produce.

The third, and the creator's most emphasised decision, is an external crystal for the ATtiny841. Internal RC oscillators can shift with supply voltage and temperature, whereas a crystal provides a dedicated and stable clock source. As a result, the controller keeps accurate timing in low-voltage situations, when a BMS can least afford to misbehave.

How It Works

The ATtiny841-SSU acts as the brain of the board, supervising the pack and managing the balancing function. Protection components sit in the power path to limit the effect of overcurrent events and voltage transients, while the crystal holds the controller's timing steady as the supply sags. The result is a simple, understandable architecture in which each part has a clear job.

Manufacturing Package

The project is ready for fabrication and assembly as published. It includes a full Gerber set covering top and bottom copper, solder mask, solder paste, silkscreen and board outline, together with an Excellon drill file, an IPC-D-356 electrical test netlist, and a pick-and-place CSV for automated assembly. Bills of materials are provided in formats prepared for several manufacturers, including a version optimised for PCBWay, so the design can move from files to a finished board without reformatting any data.

This board was designed by adrian95 and is featured here. All design work and credit belong to the original author. Please visit the original Flux project, explore the design in full, and show the creator some support.