UPS for iMac 27"! Potentially harmful ?

Discussion in 'iMac' started by IA64, Nov 20, 2013.

  1. IA64 macrumors 6502

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    Nov 8, 2013
    #1
    Which UPS do you guys recommend for the late 27" iMac ?

    I already have an Eaton AVR 1250VA but I noticed today that when electricity is down, the iMac will buzz once powered by the UPS. It's like if the iMac power supply is struggling with the load.

    That made me wonder if it could potentially damage the screen, and transistors over time.

    I do know that for home consumers, the simulated sine wave UPS is probably more than enough and can handle almost everything.

    Ideally, I should get a pure sine wave UPS but I'm not sure about the cost. A quick search and APC is asking for $400+ for the 1KVA.

    Any recommendation is appreciated.
     
  2. silvetti macrumors 6502a

    silvetti

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    #2
    I'm actually also interested in this as I plan to get an UPS for my ordered iMac, let me know if you find more info IA64.
     
  3. FreemanW, Nov 20, 2013
    Last edited: Nov 20, 2013

    FreemanW macrumors 6502

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    #3
    While this has enjoyed exhaustive coverage with multiple threads . . . . .

    As for the behavior/sound you're experiencing . . . . you may need to replace the battery in your UPS or retire the unit.

    My late 2012 27" iMac is plugged into a CyberPower 1500AVR unit.

    That seems to be the model of choice here in the iMac forum. ;)
     
  4. IA64 thread starter macrumors 6502

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    #4
    Actually the buzzing sound is not coming from the UPS but from the iMac itself. At max brightness the sound is more noticeable. If I lower the brightness that would make it less audible.

    From what I read on different technical websites, they all agreed that commercial UPS can harm TVs and displays as the output is not a pure sine wave; it's more a simulated, stepped or pulse width modulation sine wave.


    So far, I'm leaning toward the Cyberpower CP1300EPFCLCD

    Note: My UPS is 3 months old.
     
  5. kitsunestudios macrumors regular

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    Apr 10, 2012
    #5
    Wall power is AC, batteries are DC. A UPS has to convert DC to AC for the plugged-in components.

    Cheap UPS systems approximate that sine-wave voltage change in a digital "stepped" manner. Some power supplies are sensitive to this choppier change in voltage. That might be what's causing the buzz.

    Some of the more expensive UPS models offer "pure sine wave" output, which should eliminate the buzz.

    I don't actually know if the buzz is actually damaging to your system, or just an annoying noise.
     
  6. hfg macrumors 68040

    hfg

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    #6
    The stepped waveform doesn't supply as much energy (see power factor) as the pure sine wave does, thus your computer power supply has to work much harder to supply the load. This is only an issue while on battery (emergency) power, the rest of the time (normal) your computer is running directly off of the AC wall power.

    I use only sine wave UPS for my computer systems ... it is worth the small price increase to me to avoid damaging my computer power supply in the event of a power failure.
     
  7. IA64 thread starter macrumors 6502

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    #7
    Exactly what I thought. thanks.

    What brand/model are you using ?
     
  8. hfg macrumors 68040

    hfg

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    #8
    Mine are APC "SmartUPS" 1500 units

    You might be able to use a smaller one with a iMac. Don't put your laser printer on the battery supported outlets however!
     
  9. IA64 thread starter macrumors 6502

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    #9
    Well the thing is that I have a Lacie 4TB RAID/0 external storage connected, one ADSL modem, one Apple Airport Extreme and an external DAC.

    Gotta check the power consumption the max power consumption of the i7 BTO iMac and AP extreme.
     
  10. Nuke61 macrumors 6502

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    #10
    My 27" iMac is connected to a pure sine wave UPS, and my 2nd monitor, cable modem and wi-fi router is connected to a simulated/stepped sine wave UPS.

    The sine wave UPS is a CyberPower CP1500PFCLCD ($200) and the stepped UPS is a CyberPower CP1500AVRLCD ($150). A stepped UPS might not cause any damage, but I'd rather spend the extra $50 and not worry whether it does or doesn't cause damage.
     
  11. Chippy99 macrumors 6502a

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    #11
    Good advice and nice try at the technical explanation, but you got that a bit wrong.

    Anyway, I agree you are indeed better off with a pure sine wave UPS. As to whether a stepped sine wave UPS will damage the iMac in the few minutes a year it might be powered by it? I doubt it, but it's a small risk.
     
  12. hfg macrumors 68040

    hfg

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    #12
    How so? :confused: :)
     
  13. Chippy99 macrumors 6502a

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    #13
    A stepped sine wave doesn't supply less energy than a pure sine wave. The shape of the wave has nothing to do with how much power is transmitted - it's the area under the curve that matters and that could be greater or smaller with a stepped sine wave.
     
  14. IA64 thread starter macrumors 6502

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    #14
    A stepped sine wave does hold a bit of DC voltage, doesn't it ?
     
  15. SteelBlueTJ macrumors 6502

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    #15
    I've gone through 2 different UPS's in the last month since I've had my new iMac. First I picked up an APC 600 at staples. It was ok but made an annoying electrical coil whine noise (not battery) constantly. I returned it and upon doing further research about sine waves, I picked up a new Cyber Power CP1000PFCLCD UPS which is a pure sine wave UPS. I have my Late 2013 27" iMac plugged into it along with my airport extreme and cable modem. The UPS unit itself seems to work great and is completely silent unlike the APC one I had before. But now, even though it is pure sine wave, I get a random muffled buzz once in awhile coming from the bottom left center of the iMac. It comes and goes and isn't loud, but it's annoying because I know it's there and shouldn't be. I'm not sure if it's from the UPS or not and I'm not sure what to do about it. I'm just living with it for now since it's random and not that bad. I don't recall the iMac making that slight buzz noise before installing the UPS though, but I'm not sure. I may have to unplug everything and try it out. I wanted the UPS because my outlet in my room is on the same circuit as some of the stuff in the kitchen. My desk lamp dims when someone turns on the garbage disposal.
     
  16. IA64 thread starter macrumors 6502

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    #16
    Ok I'm gonna hold my horses on the Cyberpower as I was going to order the PFC 1350VA Tomorrow.

    Does your iMac make that buzz noise only when UPS is running on batteries ? If not then I am not sure it has anything to do with the UPS.

    As far as I know the UPS has a built-in voltage regulator and it won't provide power unless your AC source goes below 88 Volts.

    Have you tried bypassing the UPS and powering on the iMac from the AC source directly to see if the buzz is still there ?

    Appreciating your feedback !
     
  17. Nuke61, Nov 21, 2013
    Last edited: Nov 21, 2013

    Nuke61 macrumors 6502

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    #17
    You have an line interactive UPS, meaning that when you have normal power available, the power for your computer is coming from the wall outlet and not the battery. I'd be very surprised if your iMac acted/sounded any different if plugged directly into the outlet.
     
  18. IA64 thread starter macrumors 6502

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    #18
    What's the function of the built-in AVR then ?
     
  19. Nuke61 macrumors 6502

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    #19
    My prior explanation was a bit simplistic. An UPS can be online, interactive, or offline. An online UPS costs many hundreds to the thousands of dollars, but it provides full time battery backup and power conditioning. The AC goes directly to a charger, then to the battery, and then is converted back to AC. It provides the highest protection, but at the highest cost.

    The most basic protection is an offline UPS that switches in the battery when voltage goes low. These offline UPS are typically (only?) of the stepped sine wave type. In the middle is the line interactive UPS, which has an AVR section that stays online, while the battery backup is still only switched into the circuit if voltage drops below the ability of the AVR to handle it. AFAIK, all pure sine wave UPS's are the interactive type. The can also be the stepped sine wave type too.

    ----------

    As an FYI, I've used everything from basic $50 offline UPS to my current setup of a CyberPower 1500VA sine wave UPS with 2 iMacs, and I've never heard any buzzing except when on battery power with a stepped sine wave UPS.
     
  20. IA64 thread starter macrumors 6502

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    #20

    That's it.

    http://www.youtube.com/watch?v=tgE9VNIKhaQ


    I'm getting one tomorrow ! crossed fingers.
     
  21. alksion macrumors 68000

    alksion

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    #21
    How beneficial is UPS when I never have power outages and my computer is off when I'm gone? I just don't really see the point in my case that's all.
     
  22. silvetti macrumors 6502a

    silvetti

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    #22
    If you have poor electrical wiring at home, if a thunder hits some electrical post close by and you have your mac powered off but connected to electricity.

    BUM :D
     
  23. alksion macrumors 68000

    alksion

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    #23
    Power surge? Also I live in so cal. We don't get much lightning.
     
  24. IA64 thread starter macrumors 6502

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    #24
    I have blackouts almost everyday. My iMac is ON 24/7 as well.
     
  25. alksion macrumors 68000

    alksion

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    #25
    I see the purpose for it then in your case.
     

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