iMac 5K loud buzz when using UPS

Discussion in 'iMac' started by AdiosVista, Jul 3, 2017.

  1. AdiosVista macrumors 6502

    Sep 10, 2008
    Like the title says, I'm getting a loud from my iMac 5K only when the power is out and the UPS switches to batteries. It's a CyberPower CP1500AVRLCD (stepped wave, not sine). I know sine wave would likely cure the problem but my question is: will the buzzing hurt the iMac, or is just an annoyance?
  2. Darajavahus macrumors member


    Aug 8, 2015
    Are you sure the buzz is coming from iMac not the UPS? If from UPS that's normal I guess (mine is sine cp900epfclcd), mine also signals loudly, couple minutes to turn off the mac.
  3. b06tmm macrumors regular


    Jul 23, 2009
    South Louisiana
    I have a few APC 1500PFCLCD's (sine wave) and only hear a click and see a message on my computers when the power goes out.

    If you are hearing a buzz from the computer I can't imagine it would be good, but that's my experience from when transformer coils lose their insulation in power supplies. This may not correlate.
  4. Smoothie macrumors 6502a

    Jun 23, 2007
    I could be wrong, but I don't think the iMac would turn on at all if the power supply was getting stepped AC and it required a pure sine wave. I had a Dell years ago where that happened and I was forced to buy an expensive server-grade UPS. Every UPS makes a very audible noise when it kicks in. If that's the source of the noise, it's normal. If you're sure the noise is coming from the iMac, I wouldn't use the UPS.
  5. Ph.D. macrumors 6502

    Jul 8, 2014
    DO NOT use a "stepped" wave DC backup on something as delicate as an iMac. Only a high-quality "pure" sine wave UPS should be used.

    Will it damage it? Yes. Its power supply is evidently struggling hard to cope, hence the buzz.
  6. CWallace macrumors 603


    Aug 17, 2007
    Seattle, WA
    I have used an APC Back-UPS Pro 1500VA stepped-wave UPS for a decade with my iMacs (including a 2015 5K) and never heard any kind of whine from the iMac when on UPS-only power.
  7. Smoothie macrumors 6502a

    Jun 23, 2007
    I've used stepped wave AC from a UPS on a lot of sensitive electronic equipment with no problem at all. However, some power supplies expect pure sine wave AC and won't tolerate the approximate waveform generated by a stepped wave UPS. If the OP hears noise coming from his iMac only on the UPS power, I'd try a pure sine wave UPS to see if that solves it.
  8. geoelectric macrumors 6502


    May 19, 2008
    Wonder if it's the speakers. AV equipment doesn't care much for stepped and the iMac is an all-in-one so might be sensitive to that.
  9. bryan85 macrumors regular

    Jun 18, 2010
    had the same problem. as others have said, don't use stepped wave. you need pure sine wave ups. i went from APC to CyberPower and now have no issues. its you power supply buzzing because of the stepped wave.
  10. AdiosVista thread starter macrumors 6502

    Sep 10, 2008
    Thanks everyone for the replies and sorry for the delayed follow up.

    The buzz is definitely originating from the iMac itself and only when the UPS is running on battery.

    geoelectric, you bring up a good point, the sound does come from low on the iMac, around where the speakers are.

    Ultimately, the consensus seems to be get a sine UPS. I appreciate the feedback!

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