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  1. #1
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    Another noob question...

    If I wanted to power two LEDs at 350mA which of the two options would be better, or does it really make a difference?

    1) LEDs wired in parellel, and a 700mA driver

    2) LEDs wired in series, and a 350mA driver

    My understanding is that in the first method I could use a lower voltage, but the amperage goes up, so battery life is reduced.

    That sound right? Is there a down side to doing this?

    Thanks!

    dj

  2. #2
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    you kinda got the right idea, rather than trying to design something this way why dont you start with objectives, for example, you would like to run 500 lumens off AA cells. then choose the drive voltage and emitters from there. again what your thinking really only tells half the story. for example, you could run a mc-e at 700ma parallel and end up with only 175ma effective to each die, you could run a smaller battery say 6v and have pretty piss poor output. but you could also run 700ma in series, and need a 14v battery to even drive it, but you wouldn't be working with dismal output numbers. ya dig?

  3. #3
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    Quote Originally Posted by dustjunkie
    If I wanted to power two LEDs at 350mA which of the two options would be better, or does it really make a difference?

    1) LEDs wired in parellel, and a 700mA driver

    2) LEDs wired in series, and a 350mA driver

    My understanding is that in the first method I could use a lower voltage, but the amperage goes up, so battery life is reduced.

    That sound right? Is there a down side to doing this?

    Thanks!

    dj
    Think of it this way.... if you run 2 LEDs wired in series and use 18650 cells then one cell per led would give the required voltage so you could use a 2 cell series wred battery pack but the pack would not have a high capacity.

    If you run 2 LEDs wired in parellel then you would still have to use the same 2 cells to power them only the cells would be wired in parellel to give the required amps but with the required lower voltage.

    These are just examples and I have left out voltage required for driver ect.

    Same size battery pack, same light output and (I think) the same run time.

    However I would choose the series wired LEDs as not all LED's are the same (one may be from a different batch) and unless they both have the same vf you may find that when wired in parellel one will be brighter than the other ( trying to steal all the juice ).

    Hope that makes sense, it's late
    Last edited by yetibetty; 04-13-2009 at 09:20 PM.

  4. #4
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    Anybody add a low voltage indicator to their DIY light? If so, did you find something off the shelf, or make one?

    dj

  5. #5
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    Reputation: Jim Z in VT's Avatar
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    Quote Originally Posted by dustjunkie
    Anybody add a low voltage indicator to their DIY light? If so, did you find something off the shelf, or make one?
    see posts #28 and 29 of this thread

    JZ
    It's not about speed, it's about lack of control.

  6. #6
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    http://www.uoguelph.ca/~antoon/gadgets/batt324.htm

    Here is another circuit I have been shown. Havent tried it yet but it looks pretty simple and the parts aren't expensive.

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