My UPS Pal Puts Your UPS on the Network

Uninterruptible power supplies (UPSes) keep computers, networking equipment, and other electronics running during a power outage. But how do you know if the battery is still healthy or how much runtime you have left? Many UPSes provide this information over USB, but accessing it requires a connected computer. To make things easier, developer Aron Reid created My UPS Pal, a compact ESP32-based board that puts an ordinary USB UPS on your network.

The idea came about after Reid discovered that the UPS protecting a security camera in his garage had a dead battery. Without a nearby computer to monitor the UPS, the problem went unnoticed until the backup power was actually needed. Rather than dedicate a Raspberry Pi to the task or buy an expensive proprietary network card, Reid decided to build a cheaper alternative.

My UPS Pal is built around an Espressif ESP32-S3-WROOM-1-N16R8 module with 16 MB of flash memory and 8 MB of PSRAM. The 36×58 mm board includes a USB-A host port for communicating with a UPS, a USB-C port for power and programming, status LEDs, and a header for an optional 0.96-inch OLED display. It also includes a header exposing spare GPIO pins for connecting additional hardware.

The board runs a Network UPS Tools (NUT) server, allowing compatible software to monitor the UPS over Wi-Fi. Supported clients include Home Assistant, Synology, TrueNAS, Unraid, and Proxmox. Depending on what information the UPS provides, users can monitor battery charge, estimated runtime, voltage, power consumption, and operating status.

A built-in web interface provides access to live readings, historical data, and an outage log. Users can also initiate battery self-tests, control audible alarms, and issue shutdown commands when supported by their UPS. For remote access, My UPS Pal includes Tailscale connectivity, allowing access without exposing the device directly to the internet.

There were lots of bumps in the road during the development of the device. Early prototypes had insufficient memory for Tailscale, USB-C power issues, and a backwards OLED connector that destroyed a display. These problems were eventually addressed, resulting in a functional device that consumes approximately 0.4 watts during normal operation.

My UPS Pal is available as a preassembled board starting at $33, with an OLED-equipped version selling for $41. For those who would rather build their own, Reid has published the firmware, documentation, and original hardware design on GitHub. The firmware can also run on compatible ESP32-S3 development boards, making this an accessible project for anyone looking to add network monitoring to an existing UPS without spending a fortune.