CMOS Battery Simulator Circuit
A rechargeable solution for leaky clock batteries
Introducing the Battery Capacitor Emulator Module (BCE) – a game-changing solution for retrocomputer and gaming console collectors who need to remove corroded CMOS batteries or tech enthusiasts wanting to upgrade a PC from using coin-cells to a rechargeable setup.
The module is elegantly designed to only require single-layer PCB and absolutely no jumper wires while measuring 1.05 inches in width, and 4.1 inches in length.
Keep Time, Protect Hardware, and Extend Lifespan
Every computer, from classic retro machines to modern PCs, relies on a clock that can keep time even when powered off. Historically, this function has been enabled by CMOS and clock batteries, essential for tasks ranging from maintaining BIOS settings to synchronizing online connections through accurate time tracking. Yet these batteries–whether on legacy computers like the IBM PC AT, the NEC PC-98, or gaming consoles like the original Xbox–bring hidden risks over time. Rechargeable clock batteries, though practical in their day, are prone to losing charge capacity and can cause severe damage due to corrosion when they eventually leak, threatening the continued use and long-term preservation of these systems.
The BCE Module solves these issues by providing a direct, risk-free replacement for rechargeable batteries. With its modular supercapacitor-based design, the BCE not only reliably keeps time but also eliminates the risk of corrosive leakage. Unlike traditional batteries or aging electrolytics with limited lifespans, the BCE supercapacitor is built to endure 100,000 to a million charge-discharge cycles, significantly extending its operational lifespan and preventing degradation caused by frequent charging.
Extensive Protection Features with Fault Identification
The BCE Module goes beyond simple timekeeping with extensive protection features for maximum reliability and ease of installation. To safeguard the supercapacitor and connected components, the circuit includes overvoltage and reverse-polarity protection. Additionally, the BCE is equipped with indicator LEDs that provide instant visual feedback. These light up to indicate an overvoltage or reverse-polarity condition, enabling users to immediately identify incorrect installations. This thoughtful design adds another layer of security, reducing the chances of the supercapacitor leaking or venting, even if connected improperly.
Seamless Compatibility
The BCE Module is engineered to replicate the behavior of rechargeable cells with impressive accuracy. It utilizes a clever network of transistors, Zener diodes, and resistors, carefully tuned to mimic essential battery characteristics like charging current, float voltage, and internal resistance. This meticulous design ensures compatibility with a broad range of motherboards and systems, making it straightforward for hardware enthusiasts and collectors to install without compromising functionality.
The above chart demonstrates the device's performance during a voltage sweep from -10v (reverse-polarity) to +15v (overvoltage). As can be seen, the capacitor voltage V (white line) never exceeds 5.4v during overvoltage which is well within the specifications of 5.5v supercapacitors, while also never exceeding -1.0v in a reverse-polarity misconfiguration. While any negative voltages are undesirable, they can be tolerated for short durations, with the module rapidly discharging a negatively charged capacitor back to 0v when power is removed to further protect it from degradation.
Configuration Options
The BCE Module offers two flexible installation options, accommodating various retro systems:
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Direct Replacement: In systems with a rechargeable clock battery, the BCE Module can be connected to the motherboard by directly soldering two wires to the original battery's contact points, replacing it seamlessly.
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Rechargeable Conversion: For systems originally designed with a non-rechargeable coin cell, the BCE Module enables a solderless upgrade to a rechargeable setup. By attaching two wires to the coin cell holder's terminals (via clips) and routing a third wire to a suitable power source (the +3.3V rail, or +5V standby rail with a 3.3V buck converter), users can adapt their systems with ease and enhance clock functionality.
Future-Proof your Systems
Whether you're preserving a retro PC or a classic gaming console, the BCE Module is the ideal long-term timekeeping solution. With durability, reliability, and protection in one compact module, it ensures that your treasured machines stay intact and fully functional for years to come–without the dangers of battery corrosion.
Download high-resolution PCB schematics: [bce_schematic.zip]
Contact to purchase modules, or license the schematic for production.