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Thread: LIPO Voltage Drop Question.

  1. #1
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    LIPO Voltage Drop Question.

    Hello,

    I am running a quadcopter with a brushless gimbal 2 axis with gopro hero3.

    Setup is DJI 900kV motors , DJI 30a esc , 400mW VTX , NAZA+GPS. , EZOSD.
    Total weight including 5100mah battery is around 2000grams. 1600grams without battery.

    On the ground with everything plugged in voltage is 16.7v and EZOSD reports 0.6a drawing from the battery.

    On take off and hovering, voltage drops to 15.7v and EZOSD reports 26-28a drawing from battery.

    Is this normal ?? I have two of the same batteries and both doing same thing.

    Thanks

  2. #2
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    Can bad ESC's cause more amps to be drawn from battery ?

  3. #3
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    Ok this is my weird backwards logic. Firstly, I have no idea so lets see what I can come up with.
    5100mah = 5.1 amp hours
    26 amps = 26 amp hours to run for one hour
    26 amps = roughly 5 times 5 amp hours
    so 1 hour / 5 = 12 minutes of flight time.

    Sounds about right to this noob.

  4. #4
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    All batteries drop voltage under load. The bigger the load the more the voltage drop. Old, well used batteries drop faster than new/fresh batteries. The voltage of a 65C battery will drop less than the voltage of a 35C battery of the came capacity.

  5. #5
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    The higher the internal resistance of the cell, the more your voltage will drop at a given load. Old and low C batteries have higher internal resistance.

    If this is a 25c pack, 1v drop at 26 amps is acceptable.

    If this is a 90c pack I'd be asking for my money back.

  6. #6
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    You will always see voltage drop under load on any battery. The thing that sets apart good batteries from better batteries is lower internal resistance. This lower resistance means less voltage drop under load, which equates to more power to the prop.

    Bad settings on an ESC can cause your system to pull more current than it really should (read-inefficient) so that in turn would cause more voltage drop than normal. That being said, I don't think you have a problem.
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  7. #7
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    Don't forget temperature. On a cold morning you will see a lower voltage under load.

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