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Thread: unsure of battery life calculation

  1. #1

    Thread Starter
    eXtreme Programmer .paul.'s Avatar
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    Question unsure of battery life calculation

    I'm trying to calculate the life of a battery:

    duty cycle: 3%
    current drawn during activity: 1.53 mA
    current drawn during inactivity: negligible
    transmission time: 33 ms
    battery capacity: 2510 mAh

    here are my calculations, but I could be wrong here:

    Battery capacity: 2510 mAh
    Current drawn in 1 hour = (1.53 mA / 3%) x 100%
    Current drawn in 1 hour = 51 mA
    Battery life in seconds = ((2510 mAh / 51 mA) x 60 minutes) x 60 seconds
    Battery life in seconds = 177176.47 seconds
    Battery life in seconds = 1.77 x 10^5 seconds (3sf)

    any advice would be appreciated, as I really want to get a clear understanding of this calculation, + the tuition I received was inadequate. thanks

  2. #2
    PowerPoster boops boops's Avatar
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    Re: unsure of battery life calculation

    If the duty cycle is 3% that means that the device is active only 3% of the time. So you need to multiply the current drawn by 3/100, not divide it. You don't need "in 1 hour" on lines 2 and 3. So in my view your calculation should be:

    Battery capacity: 2510 mAh
    Current drawn when active = 1.53 mA
    Current drawn, average over duty cycle = 1.53 mA * duty cycle = 1.53 * 3 / 100 mA = 0.046 mA
    Battery life in hours = 2510 mAh / 0.046 mA = 54565 hours
    Battery life in seconds = 54565 * 3600 = 196,434,000 seconds
    Battery life in years = 54565 / 24 / 365 = approx. 6 years.

    But don't get too excited. In the real world batteries run down even when you are not using them. Normal NiMH batteries (which I guess you are using given the capacity) lose about 30% of their charge per month through self discharge, so you will probably need to charge them once in 3-4 months if that is the type you are using. Li-Ion and special low-discharge NiMH batteries keep their charge much longer.

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  3. #3

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    eXtreme Programmer .paul.'s Avatar
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    Re: unsure of battery life calculation

    thanks for the reply boops

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