Hopefully this is the right place to ask.
I have an APC Back-UPS XS 1400U that I use to keep my home server running 24/7.
It was purchased in 2015, batteries replaced around 2020, everything was fine until around June 2023 when it started randomly switching to battery for a few seconds for no apparent reason once or twice a day.
The UPS is connected to my home server via USB so I can get some readouts. It says “Unacceptable line voltage changes”, but it’s configured to switch when it’s outside the 160-280v range and it gets nowhere near those thresholds, the voltage fluctuates in the 224-234 range.
I connected an oscilloscope to the mains to see if there were transients when the problem occurred but I don’t see anything out of the ordinary and the problem has been getting worse, now it switches an average of 50 times a day.
The UPS still works, it can keep the server up for hours if I unplug the power, so the batteries should be good. What’s going on?
It could also be noise on the line, try introducing a ferromagnetic filter (low pass filter) to see if the situation improves.
Check also that the occurrences are not linked with the activation of an electric motor. I one bought a meat grinder that evertyime was on the analogical radio got only noise. And they even were not connected to the same circuit.