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  1. #1
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    Switchback 2 - Retrofit suggestions

    I have a Princeton Tec Switchback 2 [dim light, proprietary battery connectors] that gave up a very pathetic ghost a while back. It has a small aluminum head, wonderful build quality and great bar/helmet mounts. I pulled it apart the other day and ripped out the guts. [pics later] It has very shallow optics, in the 12mm depth range. The whole head is Al except for the optic cover.

    What I'd like to do is jam in a couple of decent emitters and a new driver, but it's really tight in there. I was thinking 2 XP-G on stars with the 10mm mini-optics for a spot. Running those at full power shouldn't produce more heat than can be safely conducted to the body. The bigger problem is the driver. I have 7 battery packs, all of them 14.8V. That means using a buck driver that can push 750mA. In a perfect world I'd just use a B2Flex, but I don't think it will fit without grinding out a lot of the interior metal. What other driver would y'all suggest? Should I take a different approach entirely with the build?

  2. #2
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    With those 14v batteries, and shallow optics, it is the perfect candidate for a couple 20mm triple boards and a maxflex.
    Run it at lower current so it doesn't overheat.
    2 triple xpg boards run at 700ma will give you about 1600 paper lumens.
    With a 2400mAh battery you would get over 2 hours of runtime.
    Can it handle the heat?
    I dunno.
    But even run at 350ma you'd get over 800 lumens.
    Probably the more expensive upgrade, but it would be fun.
    Look, whatever happens, don't fight the mountain.

  3. #3
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    What are the dimensions of the reflectors? 20mm ish? I'd be tempted to fit and XM-L+optic and XP-G+Regina in there with a B2flex (grind away!). To increase the depth of the optic area (or inc. the max allowable optic length), you could always cut out a piece of thin lexan and use a couple of longer screws to hold it in place over the existing cover. How much would that get you? 4-5mm? Might be enough.

    If so, that would come to $60, which wouldn't be a huge amount.

  4. #4
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    Quote Originally Posted by pinkrobe
    I was thinking 2 XP-G on stars with the 10mm mini-optics for a spot. Running those at full power shouldn't produce more heat than can be safely conducted to the body.
    I would not bother to use the 10mm optics unless you are wanting a pretty floody beam. Ledil Tina RS optics will fit in your 12mm depth and have a 16mm dia. They are not that tight either, but better than the carclo 10mm series. 2 XPGs at 1000mA will be cool enough while riding. If stopped that housing will get hot.

  5. #5
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    Quote Originally Posted by Vancbiker
    I would not bother to use the 10mm optics unless you are wanting a pretty floody beam. Ledil Tina RS optics will fit in your 12mm depth and have a 16mm dia. They are not that tight either, but better than the carclo 10mm series. 2 XPGs at 1000mA will be cool enough while riding. If stopped that housing will get hot.
    This sounds like a good solution. Any reason to use the XPG moreso than the XML@1500mA?

  6. #6
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    Pinkrobe, just throwing this out there.

    why not cut a plate that will fit between the existing black lense cover and the grey light body. Obviously include cutouts to make room for the stars and optics. Swap out the existing screws for longer ones and then you can fit any depth of lense in there you like, you'll only be limited by lense / reflector diameter. Cut the plate out of 2, 3 or even 4mm al, sandwich plates together to give you greater depth.

    JezV has shown here that "laminated" housings can work well.

    I think this will give you a much greater choice of opticss to tailor the beam to what you want

  7. #7
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    Sorry for the delayed reply. Lots of other stuff going on lately!

    I'm thinking of combining techniques. I will have to do the Al laminate to build up the available area behind the emitters so I have room for a b2flex. That will also provide plenty of heat sinking. Emitters will be XP-G with the Tina RS optics. Should be a good build...

    Thanks!

  8. #8
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    Quote Originally Posted by Vancbiker
    I would not bother to use the 10mm optics unless you are wanting a pretty floody beam. Ledil Tina RS optics will fit in your 12mm depth and have a 16mm dia. They are not that tight either, but better than the carclo 10mm series. 2 XPGs at 1000mA will be cool enough while riding. If stopped that housing will get hot.
    I second this. I just setup 2 XPGs with 10mm carclo tight/narrows. Running at 1.2A total (0.6 per emitter) it is a pure wall o' light. Exactly what I wanted for running at night, and for use as a task/barbecuing light.

    30 to 50 yards is about the end of useful throw for my set up (not so great for a bike light). Granted, you put enough of these together, and drive them hard (ala Troutie), you get a huge wall o' light that reaches out there. This housing cant take that kind of juice.


    Quote Originally Posted by pinkrobe
    Sorry for the delayed reply. Lots of other stuff going on lately!

    I'm thinking of combining techniques. I will have to do the Al laminate to build up the available area behind the emitters so I have room for a b2flex. That will also provide plenty of heat sinking. Emitters will be XP-G with the Tina RS optics. Should be a good build...

    Thanks!
    Sounds like a really nice project, and I agree that it will be a good build.

    ...However, the aluminum behind the emitters will not function as a heat sink, but a heat spreader. What I mean is that heat is only removed from the light's housing when it is transferred into the air.

    So your heat sinking capacity is only measured as that part of the body in contact with the air. The work you are doing inside the housing is the very necessary job of building up a heat spreader. As I understand it, there is no advantage to going over a 5:1 or 3:1 thickness here. In other words, if the center of your emitter is 10 mm from the exterior heat sink, than a heat spreader that it 2 to 3 mm thick is the point of diminishing returns. Any thicker, and you are just adding weight without benefit.

    Sorry for the ramble.

  9. #9
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    Quote Originally Posted by P220C
    Sounds like a really nice project, and I agree that it will be a good build.

    ...However, the aluminum behind the emitters will not function as a heat sink, but a heat spreader. What I mean is that heat is only removed from the light's housing when it is transferred into the air.

    So your heat sinking capacity is only measured as that part of the body in contact with the air. The work you are doing inside the housing is the very necessary job of building up a heat spreader. As I understand it, there is no advantage to going over a 5:1 or 3:1 thickness here. In other words, if the center of your emitter is 10 mm from the exterior heat sink, than a heat spreader that it 2 to 3 mm thick is the point of diminishing returns. Any thicker, and you are just adding weight without benefit.

    Sorry for the ramble.
    Don't apologize, you raise a good point. The emitters will be almost exactly 10mm from the edge of the light body, but the plastic front of the housing is so shallow that the Al laminate will have to be exposed to air. Hopefully, the heat will flow to the sink and get drained [sorry, bad analogy].

  10. #10
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    Quote Originally Posted by pinkrobe
    ...but the plastic front of the housing is so shallow that the Al laminate will have to be exposed to air...
    The Al laminate will be exposed to outside air, or trapped air behind the lens.

    If the former, cool.

    If the latter, once the trapped air reaches the temperature of the heat spreader, no more transfer of heat is possible. This isn't bad (quite normal, rather), but is something to think about as you are projecting how many watts your housing can handle.

    I just ran some tests on my new build, and in still air at 25C I am able to run about 3 watts with 10 square inches of exposed aluminum, and I get about 3 seconds of a finger touch test on the housing (probably 60C). In a light breeze of 20C, the housing is cool to the touch.

    On a bike, I would expect your housing to handle one watt for every one to two square inches of aluminum exposed to airflow.

  11. #11
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    I totally forgot about this light for 5 months, then cobbled it together over the last couple days. It's fugly, but it works.

    Bflex, XPG. There's a 0.125" piece of Al that the emitters are AA'd to, which in turn is AA'd to the body. The Bflex heat pad is AA'd to another piece of Al and thusly attached to the body. As luck would have it, that's just enough room to get the optics in place without using a laminate set up. I was able use the existing switch on the top of the light. It casts a big blob of light, with a fair bit of close-in spill. I'll get beamshots later, but they will be fugly.

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