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  1. #1
    Senior Member BikeManDan's Avatar
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    Calculating runtime?

    I don't know why I have so many problems with these calculations but I cant get my numbers straight

    So say that I want to run 3 Cree LEDs at 350mA from a 14.8V 4.4AHr, what kind of run time is that?

    Appreciate the help

  2. #2
    Zoom zoom zoom zoom bonk znomit's Avatar
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    Roughly 15 to 16 hrs:

    Method 1
    LEDs are around 10.2v total.
    14.8v/10.2v = 1.45 * more volts than needed
    4.4Ah/0.35A = 12.6 hours
    12.5 * 1.48 = 18.2hours

    Minus 20% for driver losses, around 15 hrs.

    Method 2
    At 350mA a led is burning around 1.1w... total 3.3W
    Your battery has 14.8V * 4.4Ah = 65Wh(watt hrs).
    65Wh/3.3W = 19.7h
    Again minus 20% for driver losses = 16hrs.

  3. #3
    Senior Member BikeManDan's Avatar
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    I appreciate you taking the time to explain something so simple. I think I got it now, thanks

    Seems like I should step it up to 750mA

    3.7V per LED * 3 = 11.1V driven
    4400mAh / 750mA = 5.87hr
    5.87 * (14.8V / 11.1V ) = 7.82hr
    15% loss = 6.65hr

    Not bad at all. Can finally put my halogens to rest
    Last edited by BikeManDan; 02-23-08 at 02:13 AM.

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