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  1. #1
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    modded mag design question

    so, I think I finally found somewhere that will let me use some machines, and I wanna get a bar light going.

    I have a bunch of D-cell mag lites lying around, so I figured I'd cut one of them up to brush up on my machining skills, and make myself a bar light.

    I'm going to be machining new fins into the head, but I'm stuck on which kind. I can just use a part-off tool and cut some slots on the lathe (like many do with these), or I can do this:



    I'd like to do the latter, since it's fairly simple with a rotary table on a mill, it's easier to make a mount for, and it looks way cooler. only thing is that it's about 7 sq. in. less heatsinking area than the turned slots. trying to decide whether it's going to be worth having that extra surface area on this light.

    FWIW, It'll be a 4X cree XRE R2, cutter 17mm stars, carclo 20mm optics, maxflex driven 4S with an 11.1V lithium pack. only 15.8W of dissipated power, including the heat from the maxflex.

    also, there's going to be a fat heatsink sitting inside of everything, so that may change things.

    thanks in advance

  2. #2
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    That will easily handle 4 XREs no worries
    and on a bike light you could get it to handle 4 MCE at a push .

  3. #3
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    I made a light with 4 xre R2's (cutter MR11) and I can tell you that it gets a lot hotter than I expected. I made a one piece housing from solid 41mm diameter bar and added deep grooves and it still gets way hot.

    Your housing has a much larger diameter so you maybe OK either way but my suggestion would be to do both types of fin on the same housing.

    The pic shows my light that gets too hot and the drawn on bits are going to be milled to try and cool it a bit. Could look good on a mag head.....maybe.
    Attached Images Attached Images

  4. #4
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    yeah, I'm pretty good about dimming my lights when I stop, so they'll be at 300mA or off when I'm stopped.

    just trying to decide though. if you use the turned grooves, then heat must travel to the bottom of a groove before it gets to use any of the surface area on that groove. if you use the milled ones (in the direction of airflow), then heat will be able to progress up into the fins across the entire length of the light. might work, might not.

    plus, you've got a counter-current flow deal going on. the hottest part of the heatsink (closest to the emitters) will see the coldest incoming air (most cooling). as the air warms up, it meets up with colder parts of the light (further from the emitters). dunno if that makes a difference, but it works for fish gills and oxygen.

    doing both types of fins might work, but iunno. if I layered them, I fear that the fins would be to thin, and would bend easily during rough handling or a crash.

    also, thinking out loud: yetibetty, are you using a bflex or such with a thermal protection? or are you just feeling the light and telling that it's really hot? I'm thinking if it's the latter, your light is actually working well, since it's getting the heat out to the heatsink and away from the LEDs.

  5. #5
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    Yes bflex so fully protected from over heating, I have it set at 60 degrees and it trips just before it gets too hot to hold (after 5 mins in the house).

    All is well when on the bike and it stays just a little warm. It's just that I use it for night walks as well and I know that I made it a bit small for that.

    I never realized how much meat was on those Maglights you will be fine.

  6. #6
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    well, I might as well go for it and see what happens

    just need to use up the last 12 XRE's I have (where did these all come from???) so I can not feel so guilty about making the 15x XPE monster...

  7. #7
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    I'm doing the same with my overload of xre's - I won't buy anything new till the XP-G's come out.
    I know a lot about cars. I can look at a car's headlights and tell you exactly which way it's coming.
    Mitch Hedberg

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