Yet Another 'Help the Noob Out' Thread- Mtbr.com
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  1. #1
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    Yet Another 'Help the Noob Out' Thread

    I'm going for a cheapo first time build with the goal of good but not earthshattering light output. I am currently using an overvolted dual halogen on the bars which is fine until the battery starts to sag. I would like to add a helmet light and get better runtime than my current setup.

    As is typical I have been lurking for some time and have a fairly good grasp on what I need but I want to make sure I'm not overlooking something as the electronics side of things is not my strong suit.

    My thoughts are two double XR-E light heads (one for the handlebars and one for the helmet) using an achesalot/ameoba style square tubing housing.

    I can figure out the LED's, switches, and optics just fine but the drivers are what I am unsure of.

    What I would really like to do is split a 5Ah 7.2V NiMH battery pack I already have into two 3.6V packs, one for each light head. I've been looking at some of the cheap drivers on DX and am thinking one of
    these
    or one of
    these
    would work. I am guessing I would need two drivers per light, one for each LED? If I used one driver per light and wired the led's up parallel they would see half the current but if I put them in series it would overload the board, right?

    Thanks for any input or suggestions.

    Cheers

  2. #2
    mtbr member
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    When you'd put the leds in series you'd blow the first driver probably, the second driver will result in darkness without destroying anything. When you'd split the battery pack so you'll get 2 3.6V packs I would advice to use the 7135 boards. Best is to use 2 boards in each driver. When you can avoid putting leds in parallel then always do it.

    The only problem might be that the battery voltage can be too close to the forward voltage of the leds. I don't know what the average forward voltage is of the leds they currently have. Previous XREs had a forward voltage that is quite a lot higher then for example the current XPEs. When the forward voltage is high the leds will start to dim earlier.

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