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About working time of UPS

  1. Aug 19, 2011 #1


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    Hello, today I am going to buy a UPS (Uninterruptible Power Supply) of Power 1000W. I am thinking if we have device (100W) as load and how long can the UPS supply power to that device?

    I was told by sales that usually, UPS can work for 4 to 5 hours but do they get that time?
  2. jcsd
  3. Aug 19, 2011 #2


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    Staff: Mentor

    Last edited by a moderator: Apr 26, 2017
  4. Aug 21, 2011 #3
    You could make your own...

    Battery charger plugs into the wall and charges a 12.6 volt deep cycle battery. An inverter is connected to the battery and powers your devices. At long as the battery charger is getting power from the wall the battery stays at full charge and the power flows directly from the charger to the inverter. When the charger looses power the battery supplies power until it is discharged. This way you can increase your run time simply by adding extra batteries in parallel, without even powering down the system. In a pinch you could run some jumper cables in through your window and power it from your car for as long as you have gas.

    This, of course, is a rather crude way of doing it that sacrifices efficiency for simplicity. If your charger and your inverter are both 80% efficient then you will loose 36% of the electrical energy that passes through the device. I don't know if that concerns you or not.
    Last edited: Aug 21, 2011
  5. Aug 21, 2011 #4


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    Never believe salesmen! They may work 4-5 hrs if not supplying anything probably.
    Just check what battery your UPS contains.
    5 hrs of 100W is a capacity of typical car battery (48 Ah at 12V), but rather not of those small ones, which are usually built into UPS's.
    Most UPS-es for home usage utilise 3, 4.5 or 7 Ah sealed batteries - less than 1hr of 100W.
    Last edited: Aug 21, 2011
  6. Aug 21, 2011 #5
    I agree with the above comments...
    Of course how long it lasts depends on the energy of the battery and the power condumed by the load. For a typical 12 volt battery, you'll see various ratings...CCA (starting power at zero degrees) and the one of interest is the 20 hour amp hr rating....how long the battery will provide 20 amps until flat dead.....but it best not to discharge a lead acid wet cell battery much past 50% as that shortens life....

    Depending on what you are doing also consider an AGM battery,,,it will be a lot more expensive initially but will have the lowest life cycle cost per amp hour...in other words, it costs more but puts out a lot more amp hours.....and it charges four to five times faster than a typical wet cell lead acid battery....

    Also wet cell lead acid batteries give of hydrogen gas and some acidic fumes....so if the battery will be heavily used that may be a consideration in some environments. The AGM is sealed and so gives off no gases nor fumes....
  7. Aug 21, 2011 #6


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    Homework Helper

    On a side note, the USA doesn't require battery makers to include capacity in battery descriptions (most European contries do require this), so capicity is not stated for a lot of batteries sold in the USA (except for ones used for radio control models). In this case, you'll need to find the specs from the UPS maker, such as the APC chart linked in post #2.
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