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Thread: 2x2 LED MTB light

  1. #1
    Flashaholic* znomit's Avatar
    Join Date
    Aug 2007
    New Zealand

    Default 2x2 LED MTB light

    Hi all

    Put together a light for the mountain bike.
    Its 4 cree Q2's shining through OPTX optics driven by bflex driver. Running 2 strings of 2 in parallel.

    I wanted something with a broader beam than on my road light ( for the twisty trails...but also a narrow beam for when Im riding to the trails.

    So I designed it with two leds facing forwards and two down and to the sides. Made a little mounting plate and bent the ends up. Note if you use thermal epoxy to stick the LEDs on, and then twist the mounting plate, they will pop off!

    Had to hack part of the lens base to fit...these LEDs only have two contacts on each side not 3, the third one would fit in the space in the optics base.
    There should be another contact between the two + +

    Optics glued on

    I measured the Vf of each LED and divided them into two lots with the same total Vf so they should run at 500mA each driven by the bflex at 1A.

    The forward LEDs are directly driven (cause I always want to see whats in front) but with the side ones I can switch in a 3ohm resistor that limits their current to around 300mA(boosting the forward ones to 700mA).

    Thermal epoxy sticks em to the mounting plate which then is epoxied inside a rectangular aluminium section.

    The origninal idea was to put the bflex driver in there too but was getting a little cramped and I couldn't think of a nice way to make a remote switch mount.

    The ends are sealed up with carbon fiber. Its not a tight weave and the idea was some light would shine out giving me some side visibility. Worked really well on my road bike light (just epoxy and good side viz)but the carbon blocks most of it here.
    Mylar covers the holes in the front and the wires exit through a gromit that I will bung up with silicon. Should handle the mud well.

    A small aluminium stem bolts the light head to the front mudguard mounting point and the bflex controller and switches live in a small box on the handlebar stem (same as my road light but with the extra switch for dimming the side lights). All powered by 12 AAs.

    The beam was surprising. I didnt expect it to be nearly as good.

    Testing on the bench it was obviously a little wider than the genuine cree optics and the leds pointing down there is always a lot of light close up.
    There is not much difference with or without the side lights dimmed so I will increase the resistor in there.
    I am pretty stoked with it and may bolt it to my road bike. Maybe a helmet mount for the suddenly obsolete dual cree road light....

    LEDs from
    Bflex driver from
    Optics from
    Bits and bobs from dicksmiths electronics.
    Last edited by znomit; 09-11-2007 at 04:19 AM. Reason: spelling

  2. #2

    Default Re: 2x2 LED MTB light

    WOW looks great!!

    nice bflex usage...

    I would look @ the heat produced in this unit, with little thermal mass you would want to make the thermal path to the fork brace pretty good...

    keep up the great work!!



  3. #3
    Flashaholic* WNG's Avatar
    Join Date
    Nov 2004
    Arrid Zone-Ah, USA

    Default Re: 2x2 LED MTB light

    Great job! And nice output.
    IHMO, I think it would work better as sprung mass instead of unsprung.
    The beams would more stable and clearer if not mounted on the lower fork.

  4. #4
    Flashaholic* znomit's Avatar
    Join Date
    Aug 2007
    New Zealand

    Default Re: 2x2 LED MTB light

    Thanks for the comments!
    Regarding the heat, there is quite a large surface area, the front is 10x5cm, the mylar only just covers the holes so the bare aluminium should conduct a lot of heat into the air. Im not running each LED at 1A either, though I did on the bench for 10min and it got pretty warm. I've found that warm on the bench means cold when out riding. Especially true with the bflex as you can turn the current right down when climbing a mountain at 6kph.

    I did think about the sprung vs unsprung mounting and yes you are right, ...its just that it fits so nicely in there and doesn't take up any room on the bars! I think with the wide beam it shouldn't matter to much either.

    Going to head for the hills tonight for its first proper outing.

  5. #5

    Default Re: 2x2 LED MTB light

    I have done quite a bit of testing with Temp meters...

    So now I know that 50deg feels HOT...60deg can't be held for too long...your case temp should not really go above 60deg....things start to cook after that...we have tested out light up to 130deg!!...

    & temps tests show that wind only drops 3-10deg from the light...(depending on surface area)

    so if after a slowish ride & your light is only warm, then you are fine...LEDs are cheap anyway...its the drivers that cost... & that is all good...

    Hey, love the angled 'wings' bit... top work...

    Yea, shutup up & RIDE!!


  6. #6
    Flashaholic* LEDAdd1ct's Avatar
    Join Date
    Jul 2007
    Hudson Valley

    Default Re: 2x2 LED MTB light

    Awesome light!

  7. #7
    Flashaholic* znomit's Avatar
    Join Date
    Aug 2007
    New Zealand

    Default Re: 2x2 LED MTB light

    Ah, almost awesome...

    I think the side LEDs don't need to be angled down and maybe angled sideways more. Its lacking a bit in spread on the twisty trails. Mounting needs to be higher if not used with a helmet light. I might try a 6x25 lens on one of the front leds.

    I took it out last week in a downpour...halfway I remembered I had forgotten to seal up the grommit the wire enters through. Oops. It was half full of muddy water! I peeled off the front and flushed it under the tap. It still works fine. Im impressed with its ruggedness.
    Left it going on full overnight on the bench to dry it...the case didn't get too hot, maybe 50c. Lots of surface area means lots of cooling.
    All looking good, I should know better but I cleaned it with meths. Lenses didnt like that and now have a few hairline cracks. Oh well.
    All sealed up again, properly this time...I hope.

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