Laser mW to mAh building 3.7v battery pack.

Discussion in 'Community Discussion' started by coopdog, Feb 7, 2010.

  1. coopdog macrumors 6502a

    Joined:
    Oct 5, 2002
    Location:
    The Great Midwest
    #1
    I'm making a laser. This diode on ebay http://bit.ly/c3sXcE

    The laser is a very bright 100mW green laser, which draws 3.7V @ 650mA. It has a 60 second duty cycle. I would be using about 4 3.7V rechargeable lithium cells rated @ 2500mAh each. So 10,000mAh with a 650mA draw would run the laser for how long? I'm sure it's an easy conversion, but my calculations aren't working out.. 15 hours? Thanks! :)
     
  2. coopdog thread starter macrumors 6502a

    Joined:
    Oct 5, 2002
    Location:
    The Great Midwest
  3. drsoong macrumors member

    Joined:
    Mar 24, 2008
    Location:
    Munich
    #3
    basic physics / eletronics...

    It might be a bit harsh to say, but:

    If you can't do that calculation, building a laser might not be the best choice for a first project. :rolleyes:
     
  4. djjclark macrumors regular

    Joined:
    Feb 17, 2008
    #4
    amp hours are usually calculated using a 20 hour figure so those cells will last 20 hours with a 125 mA draw. So in parallel it is around 20 hours for 500 mA. So if you draw more like (650 mA) expect to get less time then then a 10,000/650 calculation would suggest. This all very generic however since all kinds of things (temperature, self heating, duty cycle, self discharge, etc) can effect this time. I would guess more like 10 - 12 hours. Another item that is unknown is what minimum voltage is needed for lasing and where that fits on your battery discharge curve.

    You need to think of this as tinkering and learn from your first build.
     

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