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how to calculate battery parameter for this

Discussion in 'Electronics Homework Help' started by KUMARA SHP, Aug 30, 2014.

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  1. KUMARA SHP

    KUMARA SHP

    122
    4
    Aug 1, 2014
    I need to run 1300W computer for 24 hrs 1 week
    I can calculate power I need that is 1300*24*3600*7 = 786.246MW
    can I have a battery for this I think I can not.

    however if I have way to charge battery & for six hours battery power only in break down of charging
    then power is = 1300*6*3600=28MW can I have battery for this if have cost ?

    then I need to know how to decide battery capacity?
    relationship of capacity & output power?
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    Where does the 3600 come from in that equation? There are 24 hours in a day, not 3600. There are 3600 seconds in an hour, but that's not relevant unless you're calculating joules.

    When you multiply a power figure (in watts or kilowatts) by a period of time measured in hours, the units become Wh (watt-hours) or kWh (kilowatt-hours), i.e. quantities of energy, not power. Alternatively you can express energy in joules. One joule is one watt for one second, so 1 Wh (one watt-hour) is 3600 joules.

    You have a computer that draws 1.3 kW. If you run it for 24 hours, it will use (1.3 × 24) = 31.2 kWh, or 112.32 MJ (megajoules). If you run it for seven full days, it will use (7 × 31.2) = 218.4 kWh, or 786.24 MJ.

    Battery capacities are specified in amp-hours. Multiply the battery voltage (in volts) by its capacity (in amp-hours) to get watt-hours.

    Assuming you have a 24V battery and you need 218,400 Wh, it will need to have a capacity of 9100 Ah. You might be able to achieve this with a number of truck batteries in parallel; I don't know.

    I couldn't understand your comment about charging for six hours. Those calculations assume no recharging for a week.

    All of those numbers are far more approximate than they look. There are inefficiencies and approximations involved.

    I would first try to reduce your computer's power consumption. Many fast laptops consume less than 100 watts. Next, you can reduce losses by using a computer power supply that can run directly from the battery, instead of using an inverter to step the battery voltage up to AC mains voltage.
     
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    1300W * 24H(perday) * 7(days) = 218.4KWH

    If you computer actually used a MWH in a week you'd be in the poor house in no time.

    Also, most computer's draw will vary based on load. Windows and many Linux machines will scale the cpu speed back to reduce power consumption as well as disable peripherals.
    You can power a computer from a battery, but will need to charge it often. Many car batteries are 40Ah, which equates to 480KWh.
    Using this value, you'd need over 400 car batteries to hold enough power for a week of continuous draw at peak load on the computer.

    What are you trying to accomplish? Perhaps you should use a lighter powered computer, or consider solar or some other method to produce a charge for you.
     
  4. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    480KWh Is double what he needs isnt it?
    Adam
     
  5. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    I think my brain turned off half-way through that post...
    Each battery would provide 480Wh not 480KWh
     
  6. davenn

    davenn Moderator

    13,765
    1,920
    Sep 5, 2009

    As others have said, there's some serious maths mistakes in your post

    1300W for a computer is also pretty high ---- what sort of computer have you got that is using that much power ?
    The majority of PC power supplies are around the 550W range + another around 100W for an LCD monitor


    Dave
     
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