what size of battery backup for new 24 inch iMac?

Discussion in 'iMac' started by hardhatmac, Aug 29, 2007.

  1. hardhatmac macrumors regular


    Jun 13, 2006
    My new 24 inch iMac is set to arrive tomorrow (yea!) and I'm wondering what size of battery backup I need?

    When I was buying a battery for my G5 Quad I kept buying them too small....and I'd like to get it right the first time with my iMac...

    her specs are:

    24 inch
    2.8 core 2 extreme
    4 gigs ram
    750 gb HDD

    and an occasional external HDD will need to be powered by it as well...

    I searched for a while but couldn't find the power info I was looking for.....

    what do you guys think???
  2. thejadedmonkey macrumors 604


    May 28, 2005
    from http://www.apple.com/imac/specs.html

    Electrical and environmental requirements:

    Meets ENERGY STAR requirements
    Line voltage: 100-240V AC
    Frequency: 50Hz to 60Hz, single phase
    Maximum continuous power: 200W (20-inch models); 280W (24-inch model)
    Operating temperature: 50° to 95° F (10° to 35° C)
    Storage temperature: -40° to 185° F (-40° to 85° C)
    Relative humidity: 5% to 95% noncondensing
    Maximum altitude: 10,000 feet

    I'd say just about any one will work.. most power supplies for a Dell are like 280W and up
  3. craig1410 macrumors 65816


    Mar 22, 2007
    As I mentioned in another thread, I have measured my iMac 24", 2.4G, 320G power consumption in various modes:

    1. Minimum brightness, idle CPU = 93 watts
    2. Maximim brightness, idle CPU = 127 watts
    3. Maximum brightness, max CPU = 152 watts
    4. Sleeping = 3 watts

    I run mine at minimum brightness by choice as otherwise the screen is too bright and I don't run Folding At Home or anything similar so my average CPU usage is close to idle. I therefore would use the 93 watts figure.

    To size a UPS you usually work in VA rather than watts and you can convert (roughly) between them by multiplying watts by 1.43. 93 watts is therefore 133VA.

    Of course, this just allows you to specify the minimum UPS power output but to judge UPS size you need to factor in battery capacity required for desired runtime after power failure. High VA ratings don't always equate to long run times. I'm sure there will be a formula to work this out but here's my attempt at an approximation:

    My 600VA / 420W Hewlett Packard UPS has four 6 volt, 12 Amp Hour batteries in it. That is 6x12 = 72 watt hours each or 288 watt hours total. At 93 watts my batteries would last a maximum of 3.1 hours. Of course the UPS isn't 100% efficient and the batteries can't be run completely flat so I'd probably half that figure to 1.5 hours. If I really wanted an accurate figure then I'd run a timed test.

    Don't know if this helps but I hope it does.
  4. MK2007 macrumors regular

    Aug 31, 2007
    The best answer is buy the largest size you can afford, 1000VA or bigger.

    You want long run time, not just a couple minutes for microburst outages. A large UPS will carry you through those times when you have a power outage that lasts up to an hour. Additionally, when you have a power outage in a storm, you can replace the Mac with a light and run it for hours off the UPS without worrying about having living in the dark. In the summer time you can run a fan too.

    Don't buy anything less than 1000VA. Power requirements increase over time with larger displays and new hardware you may acquire. Then too are you only going to plug in the Mac? What about your cable modem, router, desk lamp, amplified speakers, etc?
  5. craig1410 macrumors 65816


    Mar 22, 2007
    Just remember that the VA rating doesn't give a good indication of the run time. I had an Emerson 1000VA UPS which had less than half the battery capacity of my 600VA Hewlett Packard UPS which I use now.

    I'd say weight is more of an indication of run time than VA rating. Heavy is good when it comes to UPS's!! :D
  6. agore macrumors member

    Oct 26, 2006
    BUT...be aware that large UPS units have fan cooling. I made the mistake of buying an oversized Nextgrid for my system because I got a great deal on it at Fry's. The huge noisy fan made such a racket that it now sits disconnected in the closet. If I ever find myself with a remote server room to equip with a UPS, it may see service again.

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