2026-09-09

If you're running an APC Smart-UPS in your homelab, you'll know the sting of pricing up a genuine AP9631 network management card — they go for £150+ new, and even used ones hold their value annoyingly well.

OpenNMC is an open-source hardware project that slots straight into APC's SmartSlot and gives you network-based UPS monitoring and shutdown at a fraction of the cost. Jeff Geerling has done a thorough write-up and the results look genuinely promising.

The board speaks APC's serial protocol natively, so tools like apcupsd and NUT pick it up without fuss — no custom drivers or weird workarounds. You get the essentials: battery status, load, runtime estimates, and graceful shutdown triggers over the network. That's exactly what most of us actually need from a management card.

Why homelabbers should care: Secondhand APC Smart-UPS units are some of the best value in the homelab world. You can grab a 1500VA rack-mount for well under £100 on eBay. The missing piece has always been affordable network management — OpenNMC fills that gap properly.

Caveats to keep in mind: This is still a community project. You'll either need to order PCBs yourself or wait for group buys. Soldering skills help, though it's not especially complex. Firmware is under active development, so expect some rough edges. It also won't replicate every feature of APC's proprietary cards — no PowerChute integration, for instance.

If you're running Proxmox, TrueNAS, or any hypervisor that supports NUT-based shutdown, this is a genuinely useful upgrade path.

For connecting your UPS management to headless kit, an APC Smart-UPS 1500VA paired with this card is a solid combo. If you're doing any rack cabling while you're at it, our 240W USB-C Fast-Charging & Data Cable – Braided, LED Indicator is handy for powering low-draw devices nearby. Worth bookmarking the OpenNMC repo and watching for the next PCB run.