Battery Life for Changing Loads

Discussion in 'General Electronics Chat' started by craigfoo, Dec 15, 2013.

  1. craigfoo

    Thread Starter New Member

    May 16, 2013
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    0
    I'm trying to figure out how long my battery would last in these conditions:

    I have a 3Ah battery and I need to run a sequence. The sequence goes like this:

    The maximum draw would be 2 amps.

    0 secs: 1 amp draw
    2 secs: 2 amp draw
    4 secs: 2 amp draw
    6 secs: 2 amp draw
    8 secs: 2 amp draw
    10 secs: 2 amp draw
    12 secs: 1 amp draw
    14 secs: 0 amp draw
    20 secs: repeat sequence

    If I were to take this sequence and graph it out, I would think I could take the area of the curve and get Amp-Seconds and do my calculation from there or am I way off base?
     
  2. #12

    Expert

    Nov 30, 2010
    16,302
    6,812
    It really is that simple to find the accumulation of amp-hours.
    Then you consider whether you want to run your battery dead before recharging it. Most batteries wear out a lot quicker when run all the way empty between recharges.
     
  3. craigfoo

    Thread Starter New Member

    May 16, 2013
    22
    0
    Ok, I thought I was losing it.

    So that's 24 Amp-Secs for a cycle, 3 cycles per min which gives me 72 Amp-Secs for a 1 min run time.

    It would be 72 Amp-Secs/3600 Secs to get 0.02 Amp-Hours. If I wanted to know how long it would take to only run my battery down to half, where do I go from here?
     
  4. #12

    Expert

    Nov 30, 2010
    16,302
    6,812
    1.5 amp hours divided by .02 amp hours = 75 minutes at 3 cycles per minute...if I didn't slip a digit.
     
  5. craigfoo

    Thread Starter New Member

    May 16, 2013
    22
    0
    How does dividing amp-hours by amp-hours give me minutes?
     
  6. #12

    Expert

    Nov 30, 2010
    16,302
    6,812
    72 amp seconds per minute.
    72 amp seconds x hour/3600 seconds = .02 amp hours per minute of use
    Half the battery capacity is 1.5 amp hours.
    1.5 amp hours x 1 minute of use/.02 amp hours = 75 minutes of use
     
  7. craigfoo

    Thread Starter New Member

    May 16, 2013
    22
    0
    Ahha, touche. Thanks for your help!
     
  8. #12

    Expert

    Nov 30, 2010
    16,302
    6,812
    Forest for the trees today, huh?
    We all do that occasionally.
     
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