Question about driving 1 XP-G- Mtbr.com
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  1. #1
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    Question about driving 1 XP-G

    I am having a hard time tracking this down but I am sure I have seen it somewhere. I am in the planning stages of setting up bar light and one of the components is going to be a 1up XP-G Star. I want to drive the star at a constant 700mA. Is there a way to achieve this without a driver? Can I put a resistor inline to make this happen.

    Just some added information. The light will consist of two stars, a 1up XP-G and a 3up XP-G star. The 3up I plan to drive off of a b2flex with settings ranging from 350mA to 1000mA. As I said above I want to run the 1up XP-G at 700mA that will be controlled by a separate switch from the 3up.

    I am planning on running a 14.8 or higher battery pack but I am open to having a separate supply for the single that would have a 3.7V battery driving it.

    I am also wide open to suggestions here. This is my first build so I am learning from the ground up.

    I am stoked about this project though!
    Sometimes your the windshield, other times just the bug. That's life. (c:
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  2. #2
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    mmm ...it may be way easier solution to get a simple 700ma driver and run the 1 XP-G off the same battery.... example
    ..http://www.taskled.com/ccxw.html
    ...Scun.thorpe, UK

  3. #3
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    I was considering that as well, but it doesn't look like there are any CC5W drivers available. If I go this route I will probably use a BuckToot or something similar. I also thought about stripping out a MR16 XP-E light and using the driver out of it, I wouldn't get the mA that I want but the 1up is more of a back up and for use when climbing.
    Sometimes your the windshield, other times just the bug. That's life. (c:
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  4. #4
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    Here's a good site that list many drivers. Just filter.

    http://www.videofoundry.co.nz/ianman...driverlist.php

  5. #5
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    Why not run the triple at low current rather than have a whole separate led for climbing. That would be a lot more efficient than a single led at higher current. If you're doing it as a backup, then it's not the LEDs you need to worry about since they are extremely reliable. Most failures are caused by connectors, wiring, batteries, drivers roughly in that order. If your going for backup you want a completely independent system.

    To answer your question, you can't get constant current with a resistor. You can use a resistor to limit the current to a reasonable value, but it will change as the battery voltage changes. The efficiency is proportional to the difference in battery and led Vf voltage, so running a single led off a 14.8v battery will be horribly inefficient. It takes as much power to run a single led off a 14.8v battery at 700ma through a resistor as it does to run a triple off the same battery pack at 1000ma through a bflex. 10.4 watts for the single with 80% of the power being dissipated by the resistor as heat. 10.6 watts for the triple with only 10% loss in the bflex. Using a resistor only makes sense if the battery voltage is just a little higher than the led forward voltage, but then the current will change more dramatically as battery voltage changes.

  6. #6
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    Recently I found this interesting thing: 10PCS x Built In 2 x AMC7135 20mm Alu. Star Base



    It won't fit XP-G, but as an idea I find it's interesting.

  7. #7
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    i have few of those, they work well but they are luxeon and souel p4 sized i removed the diode and used a standard 5mm flashing led to drive the 7135's to create a flashing rear light,

  8. #8
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    Thanks MtbMacgyver, That is the kind of info that I am looking for. Also, let me be honest. I liked having the option to have the 1up as a backup for trail repairs and when I am stopped for a longer period, not so much for led failure. That being said, it is there and I will probably use it in conjunction for any fast DH sections and such.

    I guess I could just run 350mA on the 1up but I guess I am suffering from lumen hunger lol.
    Sometimes your the windshield, other times just the bug. That's life. (c:
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  9. #9
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    why not make a separate single XP-G headlamp? It'd be much more useful than having a second bar lamp, plus you'll get the same redundancy. I've read a lot about Teapot drivers off eBay UK, or you could use a cheap linear regulator from DX like this

  10. #10
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    That will be the next project :-) I already have a minewt so I am ok for a helmet light. For that matter I already have a 6up helmet light that works awesome. . . don't make me start to rationalize or I will drop the project and save the green for other endeavors. . . which I should do . . . see what your doing to me lol.

    I guess you live and learn, I already have a housing started with two 20mm pockets for the led boards. It can't hurt to have an extra 200+ lumens coming into play with the 1000 coming out of the 3up board. people run 3 - 4 up lights it seems a lot but instead of using 4x1up boards I am using a 1up and a 3up. If I could afford it I would run two 3 up boards, which this may morph into at a later date and time.
    Sometimes your the windshield, other times just the bug. That's life. (c:
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  11. #11
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    you never have to justify a new light, ever

    why not then why the single XP-G in series with the 3-UP? Could you then wire up a by bypass to take the single XP-G out of the loop? If you want to drive them separately I'd still use a Teapot or that DX driver. In fact, I'll be using that exact DX driver to make an XP-G commuter light off a single 18650

  12. #12
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    hmm will the b2flex handle 4 leds like this? That makes sense. I think you just change the direction I was going in for the better. Less drivers, less batteries at the cost of a bit more wiring. . . works for me
    Sometimes your the windshield, other times just the bug. That's life. (c:
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  13. #13
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    as long as you use a 5 cell battery, I can't see why not. No idea about dropping an LED out of the series though. Email George as Taskled, he's a very knowledgeable and helpful chap.

  14. #14
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    Yes, all that will work fine. But, I'm not sure why you would really want to drop the 4th led out other than maybe to alter the beam pattern due to different optics on the triple verse the single. You'll always get more light by running 4 LEDs at the same power level as 3 LEDs.

  15. #15
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    I dunno either <shrugs>, just an idea. I think it would make more sense to go with 4 but at a lower power level. Or, sell me the lone XP-G, buy another 3-up board and make a 7 cell battery That would be awesome, on many levels!

  16. #16
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    I may not drop the single out now that I have gotten your advice. I have a question in to george about the board handling this.
    Sometimes your the windshield, other times just the bug. That's life. (c:
    Mountain Biking Apparel

  17. #17
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    advice might be gilding the lily a bit, I'm not the most knowledgeable person on here I think a 2x 3up would be a much better option.. he he he

  18. #18
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    Heat would begin to play a huge roll at that point as well though, i would think. My housing is 2.25 x 1.125 x 2.5 that is before I contour and fin it.
    Sometimes your the windshield, other times just the bug. That's life. (c:
    Mountain Biking Apparel

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