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?
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and it gets nowhere near those thresholds, the voltage fluctuates in the 224-234 range.
I’m assuming you measured hot to neutral, and didn’t find any transients.
Did you put your oscilloscope on hot to ground as well? A faulty ground could cause what you are seeing.
Do you have any CFL bulbs anywhere in your house? I once had a dead CFL bulb in a fixture in my basement. Anytime I turned on my basement light, every LED lamp in the house would strobe.
I tested live to ground, live to neutral, both in and out of the UPS, and I couldn’t see anything out of the ordinary.
The input signal isn’t a clean sine wave but it’s not dirty either, I’d say it’s sine with some extra harmonics and a little bit of noise. There were no sudden peaks or meaningful variations even while the UPS was switching furiously.
I don’t have CFL bulbs, only LEDs. I can’t think of anything else that could be causing interference. I’ll try contacting the power company as suggested by @glimse@lemmy.world
Thanks for all the replies.
Just for shits and grind, how about neutral to ground? They should be bonded together in the breaker box (and nowhere else), but if there is a fault, you might see some significant potential across them.
You’ve tried different outlets?
From neutral to ground there seems to be just some noise and a bit of DC.
Yes, I tried different outlets, doesn’t make a difference. I checked the wiring inside the plug too, the connection seems solid.
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 had one that switched on constantly. I changed some sort of sensitivity setting and now it only switches on with actual power loss.
My laser printer being on the same circuit causes my UPS to trip unexpectedly even though they aren’t connected. I’ve had to move it to another breaker.
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.