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Thread: Best voltage for P60 flashlight modded w/external pack?

  1. #1
    Enlightened
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    Default Best voltage for P60 flashlight modded w/external pack?

    Longtime member (though longtime) dormant here ... I've been running DIY halogen bike lights with overvolted MR16 halogens for years, but I'm thinking it's time to finally upgrade to LED. Not really interested in the MagicShine route because of the floodiness of the beam: I spend a lot of time on shared paths and I'm not willing to subject oncoming pedestrians and cyclists to that much glare.



    Im thinking the easiest and most cost-effective way to get a reasonably throwy LED setup is to take a P60 flashlight and mod it with an external battery pack. Probably initially going with an XP-G unit for low beam use, then maybe later adding a second XM-L (likely a nailbender drop-in) for high beam use in areas where I dont have to worry about blinding folks.



    I haven't bought the flashlight(s) yet, so my options are wide open. The Solarforce units are appealing, but which voltage? I've been pretty happy with my NiMH packs over the years, and don't see a reason to upgrade, so my voltage choices are in 1.2V increments:
    • 3.6V might work with the low voltage (4.2V max) lights and drop-ins, but will the working voltage be high enough to drive these effectively?
    • 4.8V is more appealing to me than 3.6V because it means 33% more Wh out of a 5Ah pack, and would be capable of driving the new Philips bike light, should I choose to go that route in the future, and might also be capable of driving generator taillights. Should work with the medium (4.2-8.4V) lights and drop-ins, but these seem a little harder to come by. Am I limiting myself too much at this voltage? Can 4.8V effectively drive the higher voltage (4V-18V) lights and drop-ins, or is it a tad on the low side? Would 6V be better?
    • 12V is also a contender, simply because I already own packs configured for this voltage, and can also power 12V automotive accessory lights for taillight or running light use. Ive seen some reviews on dealextreme indicating that some of the higher voltage drop-ins rated for up to 18V actually run very inefficiently (and excessively hot) at voltages this high. If not 12V, what would be an optimally efficient voltage for these drop-ins?


    Thanks in advance for any advice on voltage, and also just generally on this approach for bike lighting. As long as you shim the drop-ins with aluminum to ensure proper heat transfer to the light body, do these setups run OK for an hour-plus of continuous use? Do you need to shut off the lights if you're stopped for more than a couple minutes (which I already do with my halogens)? Most of my night riding is in fairly cool conditions, 30 to 50 degrees F, although there is the occasional summertime night ride, which might involve more like 70 F.

  2. #2
    Enlightened
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    Default Re: Best voltage for P60 flashlight modded w/external pack?

    [bump]No one responded to this, but I will ... a few weeks after I posted this I bought a nailbender XM-L 3-mode module (driven at 2.8A on high). I disassembled one of my higher-voltage packs and made a 4.8V pack out of 4200mAh sub-C cells. Works great, and I get 1.5-2hr (I think ... my rides aren't usually this long anyway) on high. Much, much longer on medium or low.
    XM-L drop-in from nailbender in TurboCat light head, powered by 4xSubC NiMHs; PT EOS on the helmet; 2x PB SuperFlash; Nite Ize SpokeLit; Arc AAA Turquoise (EDC).

  3. #3
    Flashaholic pe2er's Avatar
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    Default Re: Best voltage for P60 flashlight modded w/external pack?

    Glad you figured it out

    There is no easy answer, as the answer is 'it depends'. It depends mainly on the electronics inside your P60, and what voltage the drivers are most efficient on. For my P60 (Double barrel CREE R2 bike light) voltages higher than 9 Volt will give the best result. So I use 7.4 Volt, because it was the most convenient choice ;-) It is easiest to build a 2-cell battery, charge each cell individually and put them both in series when connected to the light.

    Have fun!

    Erwin

  4. #4
    Flashaholic*
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    Default

    I dont see much improvement of high to medium on my naibender XM-L, so usually run the P60 host light on med while biking.
    With roughly 2 hours of runtime (or when using one of my XP-G @ 800 mA P60 hosts and 2+ hours of runtime) there is no real need for anything else than bringing a spare cell - if needed,
    so I cant figure the gain in compromising the rugged setup of an 1*18650 P60 host


    for me it makes no sense ...

  5. #5
    Enlightened
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    Default Re: Best voltage for P60 flashlight modded w/external pack?

    I guess not everyone has the same experience. I find the high setting to be MUCH brighter than medium. Maybe your XM-L is overheating on high, reducing its output. I do find medium (XP-G level output) to be generally sufficient for riding in dry conditions, but (at least for my middle aged eyes) high is necessary -- and just adequate -- for downhill riding in the rain. Which is more or less the norm around here from November to February.

    FWIW I can't imagine having to open up a light and change a cell after every ride. Yuck. Not the same as plugging into a charger IME.

    But I didn't end up modding the P60 after all. Here is a link to what I did instead. Works great!
    Last edited by GlowBike; 05-30-2012 at 12:46 PM.
    XM-L drop-in from nailbender in TurboCat light head, powered by 4xSubC NiMHs; PT EOS on the helmet; 2x PB SuperFlash; Nite Ize SpokeLit; Arc AAA Turquoise (EDC).

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