When Your UPS Isn’t Actually USB: Fixing a Larice 3 KVA on Unraid

My “USB-connected” Larice 3 KVA UPS refused to show up in Unraid. I plugged the printer-style cable in, expected it to pop up in lsusb, and …nothing. No logs, no enumeration, nothing. Unraid acted as if the cable didn’t exist. A quick look at the manual told me to install UPSilOn 2000 and RupsMon, two Windows-only relics that immediately screamed Megatec clone at me. That was the clue: this wasn’t a USB HID device at all.

I swapped USB cables (including one that definitely worked with a printer). Still nothing.

Different ports? Same story.

Then some Googling and it finally clicked, many of these so-called “USB” ports are just serial interfaces disguised as USB-B connectors.

They require a special USB-to-serial bridge inside the cable that only the manufacturer’s software understands.

So I ordered a USB-to-RS232 adapter, connected it to the UPS’s DB9 port, and finally Unraid reacted.

dmesg showed a new /dev/ttyUSB0. That was progress.

I installed the NUT (Network UPS Tools) plugin in Unraid and added this minimal config. auto for the port didn't work.

[larice]
driver = blazer_ser
port = /dev/ttyUSB0
desc = "Larice 3KVA UPS"

Restarted the driver, and upsc larice@localhost came alive — input voltage, battery voltage, frequency, all there. Except one thing: ups.load was always 0. Turns out the firmware doesn’t report real-time load at all. Doesn't even register it on it's own display either but I digress.

In Unraid’s UPS settings, I set:

That lets Unraid calculate estimated load even if the UPS doesn’t provide it.

It’s not perfect, but good enough for graceful shutdowns and monitoring.

If you want true power readings, you can pull them from a smart plug or Shelly/Tasmota socket, feed that into NUT’s dummy-ups driver and merge the data but that’s optional nerd territory. Might do it next weekend :)

If your UPS ships with UPSilOn 2000 or RupsMon, it’s not HID, it’s Megatec/Q1 serial in disguise.

Use the RS232 port, not the fake USB-B. Configure NUT with blazer_ser, and you’ll get everything that matters.

Next time I see a “USB” label on a UPS, I’ll assume it’s lying.