ESP32 NUT Server Bridge
Warning
Upgrading from v1.5.x or earlier? Install v1.6.x or later with the web installer, not with an OTA update.
v1.6 adds a new flash partition (coredump) that keeps crash details for diagnostics. An OTA update cannot change the partition table: the board would work, but without that partition.
When the installer asks "Do you want to erase the device before installing?", leave "Erase device" unchecked and press Next: your Wi-Fi and NUT settings are preserved. Check it only if you want a clean install (the board then restarts in configuration mode as the NUT_ESP32_Config access point).
After this one-time install, later updates can be installed via OTA again.
An open-source firmware for ESP32-S3 that acts as a standalone Network UPS Tools (NUT) Server bridge over Wi-Fi. It connects to an Eaton UPS (like the Eaton 3S 700) via USB Host and exposes its data to your local network using the standard NUT protocol (port 3493) and a built-in Web Interface.
This allows you to easily integrate your USB-only UPS into Home Assistant, TrueNAS, Synology, or any other NUT-compatible client without needing a dedicated Raspberry Pi or PC running 24/7.
🌟 Features
- Native USB Host Support: Directly reads HID data from USB-compatible UPS devices (tested with Eaton, APC, CyberPower, Powercom).
- NUT Server Protocol: Implements the standard NUT protocol, making it instantly compatible with existing NUT clients.
- Web UI & Captive Portal: Easy configuration of Wi-Fi and NUT credentials via a modern, responsive web interface.
- Over-The-Air (OTA) Updates: Flash new firmware versions directly from the web browser without touching the board.
- Diagnostic LED: Visual feedback for Wi-Fi and UPS connection status.
🔌 Supported UPS Devices
The firmware uses the official Network UPS Tools (NUT) HID mappings and supports multiple vendors automatically:
Eaton (Click to expand tested models)
- Eaton 3S series
- Eaton 5P 1U
APC (Click to expand tested models)
- APC Back-UPS CS 500
- APC BackUPS Pro 900
- APC Back-UPS XS 700U
- APC Back-UPS BX750MI, BX1200MI
- APC Back-UPS ES 700G
- APC Smart-UPS 750
Back-UPS BX series: the APC firmware of these models stops answering USB requests at irregular intervals, often several times an hour (NUT on Linux is affected too). Since v1.7.1 the board restarts on its own a few seconds after each lockup, and the UPS status keeps updating until then. NUT clients may still see the data as stale for a few seconds. (#60)
CyberPower (Click to expand tested models)
- CyberPower UT650EG
- CyberPower CP 1350C / CP1350AVRLCD
- CyberPower CP1500AVRLCDa
- CyberPower CP1500EPFCLCD, CP1600EPFCLCD
- CyberPower SL700U
Powercom (Click to expand tested models)
- Powercom SPD-750U
EcoFlow (Click to expand untested / community-contributed models)
- EcoFlow River 3 Plus
- EcoFlow Delta 3 Plus
Untested / community-contributed. These models are recognized by the driver but have not been validated on real hardware yet.
WalleCube (Click to expand tested models)
- WalleCube Smart UPS W150
- Generic / Other Brands: If an UPS is not recognized, the system will fall back to a generic stub driver. Currently, this driver cannot read dynamic stats (like Battery Level). If your UPS falls into this category, you can use the Export USB Diagnostics button in the Web UI (System Logs tab) to download a diagnostic file (
usb_diagnostics.json). Please attach this file when opening an issue on GitHub to request dedicated support or report bugs on existing drivers.
Note
USB HID Protocol Requirement: This firmware currently supports only UPS models using the standard USB HID Power Device Class (usbhid-ups). UPS units communicating via USB-to-Serial protocols (such as Megatec/Q1, USB CDC/serial bridges, or proprietary serial protocols) are not currently supported.
📸 Screenshots
| UPS Telemetry | Wi-Fi Config |
|---|---|
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| NUT Server | System Logs |
|---|---|
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| Firmware OTA | |
|---|---|
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🛠 Hardware Requirements & Wiring
- ESP32-S3 Board: An ESP32-S3 development board is required because it features native USB OTG Host capabilities. Standard ESP32 or ESP32-C3 will not work.
- USB OTG Cable: An adapter to plug the UPS USB cable into the ESP32.
Typical Dual USB-C Board Setup (e.g., Generic ESP32-S3 DevKit)
Many generic ESP32-S3 boards with two USB-C ports have hidden solder pads on the back to enable Host mode. To achieve a clean setup without manually soldering wires to GPIOs:
- Solder the "USB-OTG" pads: Find the two pads labeled
USB-OTGon the back of the board and bridge them with solder. This routes 5V power to theUSBport, enabling it to act as a Host to power the UPS USB interface. - Solder the "RGB" pads (Optional): Bridge the
RGBpads if you want to enable the built-in status LED. - Power: Connect a USB wall charger to the port labeled
COM(orUART). - Data: Connect a USB-C OTG adapter to the port labeled
USB, and plug the UPS into it.
3D Printed Case (Optional)
Turn your bare ESP32-S3 board into a finished product! We have designed a sleek 3D-printable case for this project.
Download the ready-to-print files from your favorite platform:
Source .3mf models, original .f3d CAD files, and additional photos are available in the hardware/case directory.
🚀 Getting Started
1. Flashing the Firmware
Option A: Zero-Click Install via Browser (Recommended) You can install the firmware directly from your browser without downloading any tools! 👉 Install via Browser
Option B: Manual Build via PlatformIO
- Clone this repository.
- Open the project folder in VSCode with the PlatformIO extension.
- Connect your ESP32-S3 to your PC (using the UART/UART-Prog USB port).
- Click Build and then Upload.
2. First Boot & Configuration
- On first boot (or if no valid Wi-Fi configuration is saved), the ESP32 will create an Access Point named
NUT_ESP32_Config(Password:12345678).Note: To manually force Access Point mode (e.g., to change Wi-Fi settings), plug in the ESP32 and unplug it within 3 seconds. On the next boot, the ESP32 will start in Access Point mode. (The AP no longer activates automatically upon signal loss).
- Connect your phone or PC to this Wi-Fi network.
- A captive portal should automatically open. If not, navigate to
http://192.168.4.1. - Enter your home Wi-Fi credentials and set your preferred NUT Server username/password.
- Save and reboot.
3. Usage
- Once connected to your home Wi-Fi, the ESP32 will grab an IP address from your DHCP server.
- Web Dashboard: Navigate to the ESP32's IP address in your browser to see real-time UPS stats (Battery level, Voltage, Load, etc.).
- NUT Client: Configure your Home Assistant or NAS to connect to the ESP32's IP on port
3493using the credentials you defined.
🛠 Support the Project
This project is entirely open-source and free to use. If it helped you integrate your UPS into your smart home or server rack, please consider supporting its ongoing development!
Donations will be explicitly used to purchase new UPS models for testing, ESP32 development boards, and other hardware tools necessary to improve the code and expand compatibility with a wider range of devices.
You can support the project via:
Thank you to everyone who supports this project! 🚀
📄 License
This project is licensed under the MIT License - see the LICENSE file for details.