DIY Charger Revives Nickel-metal Hydride Batteries, Offering a Safer, cost-effective Option to Lithium-ion
Table of Contents
A growing demand for portable power has cemented lithium-ion batteries as teh dominant choice for makers and manufacturers. Though, a resourceful engineer has developed a novel solution to breathe new life into a frequently overlooked battery technology: nickel-metal hydride (NiMH). This project addresses the inconveniences of recharging removable batteries while highlighting the safety and economic benefits of NiMH cells.
The allure of Lithium-ion and the Forgotten Alternatives
Lithium-ion batteries’ high energy density and compact size have made them ubiquitous in modern electronics, from smartphones to electric vehicles. It’s now commonplace to find microcontroller boards with integrated Li-ion chargers, a testament to their widespread adoption. Yet, this popularity frequently enough overshadows viable alternatives, even when those alternatives are a better fit for specific applications.
“It’s easy to forget that other battery technologies exist,” one industry observer noted, emphasizing the dominance of lithium-ion in the current market.
Among these alternatives,nickel-metal hydride (NiMH) batteries offer a compelling combination of affordability and safety.While NiMH cells generally have a lower recharge cycle count and power density compared to lithium-ion, they eliminate the need for complex protection circuitry and are less prone to thermal runaway.
Engineering to Personal Project
The creator of the Spinc, who works on industrial vehicles in Germany, embarked on this project after a failed attempt to maximize the remaining power from non-rechargeable batteries. “That failure… got me thinking about rechargeable cells,” he explained, highlighting the genesis of the Spinc.
The most important challenge was designing a compact and intuitive charging mechanism. This involved meticulously perfecting a system that picks up each battery, securely holds it between charging electrodes, and then releases it upon completion, repeating the process for each cell. The final design utilizes seven 3D-printed parts, a servo motor, a screen, and a single printed circuit board (PCB). An infrared proximity sensor detects battery insertion,triggering the charging sequence.
Engineering the Spinc: Circuitry and Software
To ensure compatibility regardless of battery orientation, the Spinc employs an H-bridge circuit, traditionally used for controlling DC motor direction, adapted for low-voltage operation. A dedicated integrated circuit (IC) manages the actual charging process, incorporating thermistors to prevent overheating.
While a microcontroller could have been used for battery monitoring, the engineer opted for a dedicated IC due to the NiMH’s relatively flat charging curve, which makes overcharging a significant risk. “Using an IC saved me from a lot of testing, and also gave me the ability to use a fast-charging mode,” he stated.
The initial IC selection proved problematic, as it was designed for charging multiple batteries in series and dissipated excessive heat when used with a single cell. A larger IC with a switched-mode regulator ultimately resolved this issue, though its availability was limited due to the declining popularity of NiMH technology.
The charging IC is connected to an RP2040 microcontroller, which displays battery status on an LCD screen, monitors the proximity sensor, controls the servo mechanism, and responds to user input via push-button controls.The entire device is powered by a USB-C socket.
Open-Source Design and Future Potential
The Spinc’s electronics are surface-mounted on a PCB with a central cutout to facilitate battery passage. The PCB was designed in KiCad and fabricated by JLCPCB, utilizing rounded corners for easier manufacturing.
All design files – including PCB schematics, a bill of materials, 3D printer files, and firmware – are publicly available on GitHub. The creator hopes this open-source approach will encourage wider adoption and further progress of NiMH charging solutions.
The result is a convenient desktop charger that offers a practical and safe alternative to lithium-ion, ensuring a freshly charged NiMH battery is always within reach.
