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  1. #1
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    Battery pack configuration efficiency.

    Is there any functional (efficiency) difference between running a linear driver (eg, the one in the "really simple XM-L") with a pack that's 4s vs 2s2p? I know that the driver will just convert the voltages to 3.1V for the XM-L, but will one yield a better power or battery life over the other?

  2. #2
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    If you want to run a single XML with a linear driver such as a Lflex and want to use four cells it would be best to wire the four cells in parallel.

    However I think that the driver you are refering to has a minimum input voltage of 6 V so a 2S2P would be the best. Just keep the battery voltage as close as possible to the LED voltage.
    Last edited by yetibetty; 10-25-2012 at 12:43 AM.

  3. #3
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    Sort of what I was expecting, but I was really looking for some science behind it. Things like efficiency graphs etc, to better understand it.

  4. #4
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    I thought the driver in that build was a buck driver - the OP is running a 14.8v battery (4s) to a single LED.

    If that were a linear driver it means it would have to burn off over 30 watts of energy in heat with that battery only running one LED. I don't see that being possible, it would melt itself down.

    George @ TaskLED states the LFlex needs to be kept under 5watt of heat dissipation, and we know George's stuff is better than the DX style drivers.

  5. #5
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    I'm certain the driver in the "(eg, the one in the "really simple XM-L")" thread is a buck driver rather than a linear driver. Telltale clue is the large inductor (coil thing with wire wrapped around it) it has.

    A buck driver lose a small amount of efficiency as the input/output voltage differential increases, but not much.

    A linear driver converts the any excess voltage to heat so it's efficiency drops drastically as the input/output voltage differential increases

  6. #6
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    This is the driver.
    T6 3-Mode Regulated LED Driver Circuit Board for DIY Flashlight (2500~3000mA 4.5~18V) - Free Shipping - DealExtreme

    I guess it must be a buck then?
    So what you are saying Vancbiker, is getting the Vin as close to the voltage required is optimal for efficiency? In that case, I am going to wire my 4 cells in a 2s2p config.

  7. #7
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    Quote Originally Posted by Biggles604 View Post
    I guess it must be a buck then?
    Almost certainly, like 99,999%

    Quote Originally Posted by Biggles604 View Post
    So what you are saying Vancbiker, is getting the Vin as close to the voltage required is optimal for efficiency? In that case, I am going to wire my 4 cells in a 2s2p config.
    Optimal yes, critical no. Look here for good efficiency info on the Taskled driver.

    b2Flex Driver Technical Information

    The DX driver will likely not match the efficiency of the Taskled driver, but the concept is the same.

    On a side note, If I were to build a light with a driver like the DX one, I would add a couple blobs of silicone between the inductor and the board. I have repaired a couple dead MS lights where vibration had broken one of the wires connecting the inductor to the board.

  8. #8
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    Awesome. That link was exactly what I was after. I just finished my first home built light, and I have the bug now. I did it all on the cheap, and had a lot of fun learning about stuff as I went along. I think my next project will be a bit more ambitious. Having access to a machine shop is handy.
    Here's the photos of the near finished light unit.

    https://dl.dropbox.com/u/4820019/closed.jpg
    https://dl.dropbox.com/u/4820019/open.jpg

  9. #9
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    Nice job Biggles604


    ****

  10. #10
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    Nice looking build! I've got a couple of these drivers sitting around too, Mainly to repair a dead magicshine that a friend won't ever remember to hand to me, lol.

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