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  1. #1
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    8* AMC7135 4-Group 2~5 Modes LED Driver 2800ma

    I'm looking to build another light with two LED emitters, either xm-l or xm-l2. Can I use one of these driver to power the two LEDs?

    I'm looking at this one from fasttech.

    I guess I'll be hooking up the LEDs in series? Is that the best way with this driver?

    Thanks in advance.
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  2. #2
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    Not sure why you haven't got a response yet, but I will have a stab at it and let the more experienced correct any mistakes. The driver you have linked to is not ideal for 2 x xm-l or xm-l2. At 2.8A the Vf is ~3.35V so if you wire 2 in series you would need 6.7V > greater than the 6V maximum for the AMC7135.

    You could wire them in parallel, but you would be limited to ~1.4A each led - not really worth it.

    The other way to wire them is a bit different - you use one led to lower the voltage to the driver. Search this forum for poorman's circuit. If you are looking at a linear driver, you might want to think about a mobydrv with more detail here

  3. #3
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    Quote Originally Posted by find_bruce View Post
    Not sure why you haven't got a response yet, but I will have a stab at it and let the more experienced correct any mistakes. The driver you have linked to is not ideal for 2 x xm-l or xm-l2. At 2.8A the Vf is ~3.35V so if you wire 2 in series you would need 6.7V > greater than the 6V maximum for the AMC7135.

    You could wire them in parallel, but you would be limited to ~1.4A each led - not really worth it.

    The other way to wire them is a bit different - you use one led to lower the voltage to the driver. Search this forum for poorman's circuit. If you are looking at a linear driver, you might want to think about a mobydrv with more detail here
    Thanks, I figure the driver may not handle two leds.

    As for the links you provided, I've seen them before and I still can make heads or tails from it. I'm sure I don't have the hardware to mod the drivers firmware. I do like the master slave idea but can't wrap my head around just yet. It is interesting and I'll look into it more for future use. For now I'll just be looking for another driver that can handle two leds.
    "By Your Command"

  4. #4
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    I asked this same question a week or so ago and got a "hacked" way of running 2 with one of these drivers:

    One more time.... clarify my mind.
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  5. #5
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    Quote Originally Posted by Knight511 View Post
    I asked this same question a week or so ago and got a "hacked" way of running 2 with one of these drivers:

    One more time.... clarify my mind.
    Thanks Knight, according to Bruce who replied to your thread the "poorman's circuit" will let me use one driver and still provide 2.8a to both XML leds. Is that correct?

    If so, I'm going to have a good at it.

    I've already upgraded a couple of the lights I've made to this driver from the ones I got from DX. This driver doesn't make the llights and brighter, but having last mode memory and three usable modes makes it better than always cycling through the different modes using the driver from DX.
    "By Your Command"

  6. #6
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    But! Keep in mind that poorman's wiring was originally ment for SSC P7 which had far higher Vf. With 2 XM-Ls you'll have voltage drop of 6.7V at most in series (usuallay less) with 1.7V left for the driver to drop. At 2.8A drive current that makes 4.76W of heat to be burnt in the driver. Make sure you keep those AMCs cooled.

  7. #7
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    Quote Originally Posted by Toaster79 View Post
    Make sure you keep those AMCs cooled.
    Thanks, i will, if and when I get this build started.
    "By Your Command"

  8. #8
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    another question regarding Poorman Mutli-LED setup method. Is it better to use XP-G2 Leds? I was thinking of using 3 xp-g2's or 1 xm-l2 and 2 xp-g2s set up with 2 or 3 8650s.

    Still new to this multi led set up and slow on the whole vf thing. But open to learning.

    Goal is to have about 800 - 1000 lumens with 2 - 3hr run time.

    Thanks.
    "By Your Command"

  9. #9
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    Quote Originally Posted by pucked up View Post
    another question regarding Poorman Mutli-LED setup method. Is it better to use XP-G2 Leds? I was thinking of using 3 xp-g2's or 1 xm-l2 and 2 xp-g2s set up with 2 or 3 8650s.

    Still new to this multi led set up and slow on the whole vf thing. But open to learning.

    Goal is to have about 800 - 1000 lumens with 2 - 3hr run time.

    Thanks.
    Two rules with a linear regulator as is being discussed here

    1. The output voltage of a linear regulator must always be lower than input voltage
    2. Closer to the output voltage is better - less to waste as heat


    The approximate Vf for 3 x XP-G2s is from 8.32V @ 0.1A to 9.75V @ 1.5A. The Vf for 1 xm-l2 and 2 xp-g2s is from 8.38V @ 0.15A to 9.64V @1.5A. In other words there is no significant difference between either set up. Similarly because you can't use the 3A potential for the xm-l2, there is no significant difference in light output either.

    2s_p x 18659 cells gives you 8.4-7.0V - ie too low for a linear regulator.

    3s_p x 18650 cells gives you 12.6-10.5V. Worse case scenario you would be burning off (12.6-9.75)*1.5 = 4.275W till the voltage drops - ie Toaster's comments also apply.

    How many lumens will depend on the bin, but just to give you an idea 3 x XP-G2s in an R5 bin will give you a theoretical lumen output of ~1,550 lumens @1.5A.

    A 2 hour runtime @ 1.5A requires ~3,000 mAh - ie a 3s1p of 3400 mAh Panasonics should do the job. To get to 3 hours you would need a 3s2p, or drop the current to 1A.

  10. #10
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    Thanks Bruce, I think I'll stick to my original idea of using 2 XM-Ls and this driver using your diagram that you posted in another thread that Knight started. With 2 XM-Ls I'll be limited to a 2S1P 18650 set up?

    Unfortunately the build will have to wait as I'll be busy the next 10 days with TIFF.
    "By Your Command"

  11. #11
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    Wire XP-Gs parallel and then in series with XM-L. So you get 2S wiring and the two Gs share 3A (1.5+1.5). Vf would be a little higher than two XM-Ls and the beam would be a bit narrower with proper optics.

  12. #12
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    Can you run two drivers in series with each one powering one xml?

  13. #13
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    Quote Originally Posted by varider View Post
    Can you run two drivers in series with each one powering one xml?
    From what I've read, yes you can. But then it wouldn't be called "Poorman's circuit."
    "By Your Command"

  14. #14
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    Wiring two drivers in series doesn't make any sense. Why are you asking? What's your goal?

  15. #15
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    Quote Originally Posted by Toaster79 View Post
    Wiring two drivers in series doesn't make any sense. Why are you asking? What's your goal?
    That way I could use my 2S2P and 2S3P batteries with the light. I thought these drivers were meant for a 1S setup

  16. #16
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    you can use one driver per LED as a Master Slave set up (2 boards, with the MCU on one controlling both of them), but you still need the input at less than 6V if you're going to use a Nanjg type linear driver.

    However, if you want to use those 2S packs, then an Lflex would work perfectly to drive 2 LEDs in series.

    Toaster - it's worth bearing in mind that the new XP-G2s have a lower Vf than the original XP-Gs. If anything the XM-L2 would be better as it's Vf is slightly higher than XM-L.

  17. #17
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    Quote Originally Posted by mattthemuppet View Post
    Toaster - it's worth bearing in mind that the new XP-G2s have a lower Vf than the original XP-Gs. If anything the XM-L2 would be better as it's Vf is slightly higher than XM-L.
    Are you sure about that - the cree product characterisation tool shows Vf @ 1.5A & 85C for XP-G as 3.08V and XP-G2 as 3.14V.

    The product data sheet shows different numbers but I think this is because the XP-G datasheet is at 25C while the XP-G2 datasheet is at 85C.

    Same issue arises with XM-L & XM-L2 in a different way - the data sheets look very close, but when you use the same thermal junction temperature as you say the XM-L2 has a higher Vf - @ 3A & 85C an XM-L shows as 3.21 while an XM-L2 shows as 3.33.

  18. #18
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    just reporting what people on CPF (Match and the like) have found in testing - XP-G2 has a lower Vf and XM-L2 has a higher Vf than previous generation parts under the same conditions. No personal experience with running XP-G2s though.

  19. #19
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    8* AMC7135 4-Group 2~5 Modes LED Driver 2800ma

    Fair enough- practical experience beats datasheet numbers any day

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