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?

  • @[email protected]English
    9•1 year ago

    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.

    • @[email protected]OPEnglish
      7•1 year ago

      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 @[email protected]

      Thanks for all the replies.

      • @[email protected]English
        5•1 year ago

        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?

        • @[email protected]OPEnglish
          4•1 year ago

          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.