Few questions on dual XP-G b2Flex build- Mtbr.com
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  1. #1
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    Few questions on dual XP-G b2Flex build

    Alright, I'm just about to start my first build here, and have a few questions (of many to come) for you guys that have a grasp on this stuff.

    My first build is a Citizen Kane style (hammond box) build using dual XP-G's and a b2Flex. This is intended to be a helmet light.
    I'm including links to everything I am using incase anybody needs to find the stuff for themselves.

    http://search.digikey.com/scripts/Dk...9-ND&x=11&y=12
    http://ledsupply.com/creexpg-w139.php
    http://www.taskled.com/b2flex.html

    I am starting from scratch with everything including the batteries.

    I have battery holders from digikey that can hold 2, 3 or 4 cells. I have at least 2 of each, so I can build bigger packs if need be.
    http://search.digikey.com/scripts/Dk...393250&k=18650

    I picked up these batteries from DX.
    http://www.dealextreme.com/details.dx/sku.26247

    For the connectors I picked up some MS Y Cables from DX.
    http://www.dealextreme.com/details.dx/sku.32753

    I picked up some 1/8" L angle at Home Depot in 3/4" which measures about 19mm to use for the heatsink. I'll most likely tap and thread this onto the box using some thermal grease I have here for building computers, using m3 screws.

    <h1> Now onto the questions</h1>

    Do you think that the hammond box setup can dissipate the heat generated by using dual XP-G's run at 1.5A without adding some kind of heatsink?

    I noticed that everybody that builds these style lights mounts the L bracket with the stars attached to the bottom of the case.
    If I did need to add a heatsink, I would mount the bracket to the top of the inside of the case and attach a heatsink to the top on the outside. This should provide a more direct thermal path from the stars/driver to the outside.
    I have several different computer heatsinks that I could toy around with. One in particular is perfect that came off a passive cooled 512mb vid card.

    So do you think I'll need to heatsink?

    Would I be better off running the whole thing at 1.2A?
    I'd like to squeeze everything I can out of the light for technical, fast, rocky descents.

    I normally run my lights on low for climbing, and med for the flats, and very rarely do I put them on high. Maybe for 15-20 min total out of the 1.5-2 hour ride, but only for a couple minutes at a time.

    Second question. Here is where my knowledge gets dicey........

    I'm torn on what configuration to build my battery packs.
    The batteries are rated at 2600 mAh, which means they are most likely 2200mAh.
    Since I don't need a ton of runtime i figured I would build them 3s1p for 11.1v.
    Would building them 4s1p gain me much runtime?
    I kind of understand how the b2Flex works as far as the input V needing to be slightly above the output V, and if you start going to far above that it starts getting much less efficient. I believe I need my input 1.7v higher.
    It seems like the board is much better suited to a 3up config, as you can get the in and out much closer.
    I don't think I can build them 2s2p, otherwise I would in a second.

    I should probably mention that I am running the 2 XP-G serial.

    Or is there a better way to do it with the stuff I have?

    I think I would have been better off with a MaxFlex driver, but they were out of stock, and I really want to get my hands into this thing. maybe for the next build I will run a max flex at 1.3A

    Do you guys see a better way to do this build with the stuff I have?
    Or should I just build it and stop overthinking it?

    So to summarize.......
    Do you think that the hammond box setup can dissipate the heat generated by using dual XP-G's run at 1.5A

    So do you think I'll need to heatsink?

    Would I be better off running the whole thing at 1.2A?

    What config should I build my battery?

    Should I hold out and wait for the MaxFlex? (this would open up battery options)

    If you made it this far, thanx for taking the time to read through my dribble....= )
    Look, whatever happens, don't fight the mountain.

  2. #2
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    Using that Hammond case, I would....

    Bore 3 18mm diameter holes in the side of the case and orient the LEDs 90 degrees to the "traditional" CK build.

    Use 3 XP-Gs at 1A. Heat will be OK as long as you get a good path from the LED mount to the case.

    Bflex and 4S1P battery will give you ~3 hrs run on high. Bflex and 3S1P battery will give you ~2.2 hrs on high, with slight dimming toward the end of the battery. Don't use the maxflex unless you are stuck on a 7.4V battery.

    3 LEDs at lower current will give more light per watt. Your housing size has ~18 sq inches of area. Enough for the ~10W this light will be.

  3. #3
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    OK my take on your questions

    No I dont think the hammond box will be enough to take 2 XPGs @1.5 amps
    if you are in a warm climate but at lower drive yes .

    no problem if using for fast bits it will stay cool at full and the B2flex if you set it up right will dim before any damage anyways

    11 volt or 15 volts the B2flex wont care which for your set up

    no you have the right driver for your proposed light config

    yes build it and stop worrying


    the cooler the more lumens coming out the front

  4. #4
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    6 xpg's run at 1 amp.









    L bracket bolted to top of case thru heatsink.
    Does it get hot, yes of course.
    Maxflex set to ramp down at 60 C, its never done it on the trail.

  5. #5
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    I'd add a low profile HS and bolt it through to the LED mounting bracket like you suggest.

    I'd also run it at L1>L3(600-700mA?)>L5 (1.5A), with threemode (L1>L3-L5), which would be more than enough for your needs and as long as you keep moving (and don't ride in the tropics) should keep cool. Make sure you pot the driver to the LED bracket and set the thermal monitoring to 60C and you'll soon find out if 1.5A is too much.

    Also, while the peeps above are correct in saying that 3x [email protected] will be more efficient, it will also be heavier (extra LED, bigger case?, extra battery). So, if you can get the run time you want from a 3s1p battery driving 2 LEDs, I'd say go for it (I did )

  6. #6
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    Quote Originally Posted by Citizen Kane
    6 xpg's run at 1 amp.









    L bracket bolted to top of case thru heatsink.
    Does it get hot, yes of course.
    Maxflex set to ramp down at 60 C, its never done it on the trail.
    that looks just like the HS I used for mine. Can't remember where I got it though - old Mac or IBM PC I think..

  7. #7
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    Thanx for the replies guys.
    I guess I overthink stuff a bit, but I'm pretty sure I'll be sticking to the plan of 11.1v battery, running at 1.5A for now.
    I may just toss the idea for the heatsink for this build, as I can always re configure the b2Flex for whatever current ends up working for me.
    I'm pretty good about turning down the brightness right when we start slowing down, so I don't see it over heating until it starts getting hotter around here.
    I will worry about the heatsinking and other gizmos for future builds.
    I do also have a couple 3up XP-G boards I was gonna use for a build in the near future.
    I'm sure I'll have many light builds in the future, as when I get into something (hobby) I jump in both feet first and run with it.
    Now if I can only talk the lady into allowing me to get a mini lathe/mill combo to squeeze into a corner of our tiny abode I'll be set!!!!!
    Look, whatever happens, don't fight the mountain.

  8. #8
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    Quote Originally Posted by Citizen Kane
    6 xpg's run at 1 amp.









    L bracket bolted to top of case thru heatsink.
    Does it get hot, yes of course.
    Maxflex set to ramp down at 60 C, its never done it on the trail.
    Thats sweet CK!!!!
    I may have to copy that here in the near future!!!
    How does it throw?
    Better for helmet or bars?
    Look, whatever happens, don't fight the mountain.

  9. #9
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    Quote Originally Posted by Vancbiker
    Using that Hammond case, I would....

    Bore 3 18mm diameter holes in the side of the case and orient the LEDs 90 degrees to the "traditional" CK build.

    Use 3 XP-Gs at 1A. Heat will be OK as long as you get a good path from the LED mount to the case.

    Bflex and 4S1P battery will give you ~3 hrs run on high. Bflex and 3S1P battery will give you ~2.2 hrs on high, with slight dimming toward the end of the battery. Don't use the maxflex unless you are stuck on a 7.4V battery.

    3 LEDs at lower current will give more light per watt. Your housing size has ~18 sq inches of area. Enough for the ~10W this light will be.
    I had thought about that Vanc, but I'll have a hard time doing any serious boring/metalwork until I can get a work nook setup here. All my serious tools are stuck in a storage unit with no place to use them at the moment.
    I do have a buddy that offered me a corner of his garage to setup a small bench for my drill press, grinder and other fun stuff.
    But for now it is all hand tools with dremel tool.

    Troutie,
    thanx for the reinforcment.
    All this talk about heatsinking i keep forgetting about the redundancy of the temp sensing!!!!

    Matt, I'll be mounting the driver to the back of the L bracket the stars are mounted to....using Arctic Allumina.
    Good call on the three mode.
    Look, whatever happens, don't fight the mountain.

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