What would happen if I...???- Mtbr.com
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  1. #1
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    What would happen if I...???

    Ran three Cree XR-E Q5 leds in series Vf of 3.3 - 3.7 on a 11.1 Li-ion battery pack?

    dj

  2. #2
    MTBiker
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    You're talking about direct drive?

    They would probably be overdriven since a nominal 11.1V battery pack actually is higher when fully charged, then they would dim.
    We can bomb the world to pieces, but we can't bomb it into peace -Michael Franti

  3. #3
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    Quote Originally Posted by kuksul08
    You're talking about direct drive?

    They would probably be overdriven since a nominal 11.1V battery pack actually is higher when fully charged, then they would dim.

    No, I would probably drive them with a Recom Driver (advertised efficiency of 96%) at 350 and/or 1000 mA.

    dj

  4. #4
    Homer
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    You'll need a buckboost driver for that combo, and they'll never be that efficient... If you up one series cell or go down one LED you'll have a good buck setup.
    Need optics for DIY bike lights?

  5. #5
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    Quote Originally Posted by brum
    You'll need a buckboost driver for that combo, and they'll never be that efficient... If you up one series cell or go down one LED you'll have a good buck setup.
    I know that is what I should do, but that is not what I am asking. I was wondering what would happen.

    dj

  6. #6
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    I took a quick look at the recom datasheet. They are asking for Vin to be 1.5-4V greater than Vout (Vf). Most buck drivers fall out of regulation if the Vin is not greater than Vf. I've never personally tried or experienced what happens at that point. I suspect that it acts sort of like a direct drive connection just a bit less efficient since you have the driver circuit loss.

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