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Power required to Elevate water

  1. Sep 22, 2012 #1
    Hi All,

    I am not an engineer or have the brains to ever be one either..

    I have (possibly) a simple question relating to the exact amount of power (Battery)required to elevate water (50 liters) 3 meters.

    Would one be able to obtain some or other peace of equipment that would provide you with an exact reading of a battery's power before and after the elevation had for instance been completed? E.g. Before 100% and after 93.37%

    Then are batteries considering eventual wear and tear to such development standards, on the level to produce exact same usage results time and time again?

    Thanking you in advance..
  2. jcsd
  3. Sep 22, 2012 #2


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    YouOne, Welcome to Physics Forums!

    1. Calculate the work needed to raise 50 liters of water 3 meters.
    2. Get equipment set up: Pump, electric drive motor, and battery, all sized to do the above work.
    3. Get a "State of Charge" meter and install it in the battery circuit.
    4. Charge the battery to 100% (fully charged).
    5. Energise, pump water.
    6. Read the State of Charge of the battery = less than 100%, obviously.

    If you repeat the above process you could expect the same results over and over. But over a long time batteries decrease their capacity and you'd probably find them getting "weaker". Just like having to repalce your car battery every few years.
  4. Sep 26, 2012 #3
    First get your terminology straight.

    Power is a rate, it is energy per time.
    Energy is what is needed to do work.
    Power is what is needed to do work in a certain time.

    Energy is measured in watt-hours, for example. Power is measured in watts.

    Since you never mentioned time in your post, all you talked about so far has been energy, not power.

    The ideal energy needed to raise 50 liters of water (50 kg) 3 meters can easily be calculated from the formula for potential energy that you studied in high school. No need to be an engineer.

    In practice the efficiency of your apparatus will not be ideal, and you will spend more than the above calculated energy. And that is also trivial to measure with an electricity meter. Again it doesn't take an engineer to know that - one such device is installed in absolutely every home, it is how your electricity bill gets determined every month. If you did not use a battery but a power outlet, you can actually use your home's electricity meter and not even need a separate one.

    The energy stored in a battery is more tricky and indicators for it are often approximate... Some indicators can be very accurate for a specific battery type but not really generic for all batteries at all wear levels.

    But an obvious generic and precise way to measure a battery's energy is with an electricity meter when you spend it. While that isn't exactly practical for a battery indicator, it is exactly what you are doing in your particular situation anyway.

    So you see, you are going at the problem a bit backwards - instead of looking at a battery indicator before and after you do your work in order to find out how much energy you spent, you should just plug in an electricity meter and get a much more accurate measurement, and then you can even use that to say how much energy there was in the battery.
  5. Oct 3, 2012 #4


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    The OP does not ask for an alternating current solution; she specifies using a battery.
    Sorry, but the "electricity meter" you described above will not measure direct current from a battery. It measures alternating current, and so it would NOT function as you claim.

    Also, providing the State of Charge indicator is specifically matched to the battery type it gives a reliable and accurate indication of energy withdrawn from the battery.
  6. Oct 3, 2012 #5
    Bobby, there are electricity meters for DC as well. OK, your house's electricity meter is a bad example in that case, but it is not the only one. A lot of DC ammeters do the integration part for you, assuming the battery does not get as discharged as to significantly affect its voltage, but if you insist on extra precision you can even get one which has a voltmeter as well.
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