Overview
I recently completed a fully custom sodium-ion (Na-Ion) battery pack built around four Na-Ion cells in a 4S configuration. The entire project — hardware, firmware, and software — was designed and implemented from scratch. This post covers the architecture, design decisions, and what I learned along the way.
Specifications
| Chemistry | Sodium-Ion (Na-Ion) |
|---|---|
| Configuration | 4S (series) |
| Capacity | 10 Ah |
| Max current | 200 A (5s), continous 75A |
| Nominal voltage | ~14 V (4 × 3.5 V) |
| Working voltage | ~11.4 V - 14.6 V |
Custom BMS
The Battery Management System was designed entirely in-house. It handles per-cell voltage monitoring, passive cell balancing, overcurrent protection, short-circuit cutoff, and over/under-voltage protection. The firmware runs on a microcontroller embedded in a custom PCB I designed and routed myself.
Charge controller
Rather than using an off-the-shelf charger, I implemented a dedicated charge controller with a CC/CV algorithm tuned specifically for Na-Ion cell characteristics. The controller dynamically adjusts charge current based on cell state and temperature readings, ensuring safe and efficient charging throughout the full cycle.
Web dashboard
I wrote a lightweight web application that connects to the pack and displays real-time status: individual cell voltages, state of charge, current draw, temperature, and event logs. The interface is accessible from any device on the local network and requires no external dependencies.
PCB & enclosure
The main board was designed from schematic to final layout, with careful attention to high-current traces, thermal relief, and component placement around the BMS FETs. The cell enclosure was also custom-designed to securely hold the 4S configuration with proper spacing and contact surfaces.
Why Na-Ion?
Sodium-ion technology is an increasingly viable alternative to lithium-based chemistries — sodium is abundant, lower in cost, and the cells do not require cobalt or lithium in their cathode. Performance characteristics differ slightly from LiFePO4 or NMC, which made this an interesting engineering challenge, particularly around the charge algorithm and BMS thresholds.
