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?
Don’t know for sure but the first thing I’d do is get a new battery. 3 years ago means it’s overdue, and if the battery is damaged or not putting out proper power levels it could be the cause. I always know it’s time for a swap when my UPSes start tripping for no good reason, although I’ve never had one go nuts like yours is. They usually just stop working if I let them go way too long between swaps.
I’m dealing with something similar but not as bad.
Our best guess is brownouts for our instance, but it doesn’t sound like what you’re dealing with. Good luck. Let me know if you’re able to find out. Hope the hardware isn’t failing.
Could be battery. That is usually the first thing to swap no matter what.
It could be whatever internal component the UPS uses to measure the line voltage is going bad. If that is the case your probably looking for a new UPS :(. Unless you want to do some very indept troubleshoot and potentially board level repairs.
Other option is to try the UPS on another circuit, or if available, another building entirely.
I would wonder about shared loads on the mains causing undesirable power factors or other electrical noise. I’d check that the mains frequency remains within specification as well: 50/60Hz ± 3Hz according to APC.
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.
