Dumb driver question...- Mtbr.com
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  1. #1
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    Dumb driver question...

    Hey folks! I'm about to order some drivers from TaskLed, and I need a wee bit of advice. I was originally just going to get the 2 MaxFlex + 1 B2Flex to build one light and repair 2 others, but then I saw two small flashlights with 25mm diameter...

    Proposed Use - bar lights for summer commuter, 1 spot and 1 flood [I have optics and reflectors on hand]
    Battery - 14.8V Li-ion pack [I have 7 of these]
    Emitters - MC-E [on hand]

    My plan is to connect the two flashlight bodies together, wire the MC-Es as 2s2p and then run the lights as serial with the driver in one light body. The downside is that if one side dies, the whole thing is done. What driver - B2Flex or MaxFlex?

    An alternative would be to put a B2Flex in each light body, and use a Y-splitter to power each one individually. Dual DIY Dinotte! If one dies the other is unaffected. The additional cost is negligible compared to the coolness factor.

    Recommendations?

  2. #2
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    25mm ID will be a tight squeeze for a b2flex as the board is 1" so slightly over 25mm. I believe you can "shave" a small amount of the edge of the boards but be careful, I have killed a board by taking too much off.

    If the 25mm is OD then forget the b2flex altogether

  3. #3
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    b2flex would work well to drive both - 1500mA drive current would equal 750mA per die, which is only a sniff over spec for the MC-E.

    The only potential downside (other than what emu26 said) is that the 14.8V packs will go out of regulation somewhere in their discharge curve, which will cause the lights to dim near the end of their capacity. Ideally you want a 5 cell pack to drive 4 LEDs (as each die is 3.x V and you have 4 in series), but a 14.8V should cope, just

  4. #4
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    Quote Originally Posted by mattthemuppet
    1500mA drive current would equal 750mA per die, which is only a sniff over spec for the MC-E.
    The MC-E will handle 1000mA just fine with a good thermal path to a good heatsink. I have run mine there for about a year now. Mine actually is a nicer color (more white) at 1000mA than 750mA.

  5. #5
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    Thanks people! The flashlight bodies have in internal diameter of about 24.5mm, so judicious sanding of the driver should allow the B2Flex to fit. Worst case - I ovalize the main body slightly [I can actually squeeze it with my hand] and jam it in there.

    I think I'll go with the dual-driver setup so I can run the lights independently. I've run the batteries on a bflex-equipped light down to the point where it's out of regulation, and it hasn't caused any damage. Better still, the dual-driver setup on 2s2p MC-E won't go out of regulation as it's only drawing ~6.8V @ 1500 mA per side.

  6. #6
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    Quote Originally Posted by Vancbiker
    The MC-E will handle 1000mA just fine with a good thermal path to a good heatsink. I have run mine there for about a year now. Mine actually is a nicer color (more white) at 1000mA than 750mA.
    that's interesting, didn't realise LEDs changed colour with current.

  7. #7
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    Quote Originally Posted by pinkrobe
    Thanks people! The flashlight bodies have in internal diameter of about 24.5mm, so judicious sanding of the driver should allow the B2Flex to fit. Worst case - I ovalize the main body slightly [I can actually squeeze it with my hand] and jam it in there.

    I think I'll go with the dual-driver setup so I can run the lights independently. I've run the batteries on a bflex-equipped light down to the point where it's out of regulation, and it hasn't caused any damage. Better still, the dual-driver setup on 2s2p MC-E won't go out of regulation as it's only drawing ~6.8V @ 1500 mA per side.
    I don't think running the light out of regulation would do any damage, only that some people don't like the dimming at the end.

    Don't forget though, that you'll need to think of some way of heatsinking the b2flex to the body if you're going to run it at 1.5A (which will also provide better temp sensing). Shouldn't be too hard if you can sit it parallel to the slug with the LED on it, but worth thinking about.

  8. #8
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    Quote Originally Posted by mattthemuppet
    I don't think running the light out of regulation would do any damage, only that some people don't like the dimming at the end.

    Don't forget though, that you'll need to think of some way of heatsinking the b2flex to the body if you're going to run it at 1.5A (which will also provide better temp sensing). Shouldn't be too hard if you can sit it parallel to the slug with the LED on it, but worth thinking about.
    Good call on the sinking. I'll likely just make two slugs, one for the star and one for the driver, press fit everything with a bit of thermal adhesive for good measure. I likely won't run it at full power very often, just on dreary, foggy days.

  9. #9
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    Quote Originally Posted by pinkrobe
    Good call on the sinking. I'll likely just make two slugs, one for the star and one for the driver, press fit everything with a bit of thermal adhesive for good measure. I likely won't run it at full power very often, just on dreary, foggy days.
    well, if you can do it with one slug (LED one side, driver the other) that would be better - more of a direct heat sensing path from LED to driver, fewer parts, plus you'll be able to assemble it all together before fitting it in. All you'd need would be a small square standoff to AA/ JB weld the driver to (on that little gold patch) and you'd be done.

  10. #10
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    Quote Originally Posted by mattthemuppet
    well, if you can do it with one slug (LED one side, driver the other) that would be better - more of a direct heat sensing path from LED to driver, fewer parts, plus you'll be able to assemble it all together before fitting it in. All you'd need would be a small square standoff to AA/ JB weld the driver to (on that little gold patch) and you'd be done.
    Ah, I see what you mean. I've never used the heat sensor function on a driver before, so I really didn't give much thought to how it actually worked.

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