3x or 2x X-ML bike light, 4x or 3x 18650 battery- Mtbr.com
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  1. #1
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    3x or 2x X-ML bike light, 4x or 3x 18650 battery

    Hello

    After reading a lot in this English forum (which is not my mother tongue - excuse my mistakes), I bought two dx direct drive torches, a P7 and a MCE single 18650, which are much better than my old Sigma evo-x/evo lightset.

    Now I would like to build my first bike light. I would like to use the new X-MLs, because of the efficiency at low Ampere-input and the light power when driven with 3A.
    I would like to build it as a compact bar-light (battery and light head together without tangling cables). To go uphill I need a low mode, about 200 lumens, which doesn't blind my friends on their mountainbikes, and to go down, I need a high mode about 1'500 lumens. Of course it would be fun to have a super bright mode to show off.
    I plan to put the X-ML in "copper pipe end cups" http://www.hgt-technik.de/_py_/a-557...eferrerIDQQ10/. I would like to use protected 18650 batteries, which I can loud separately, because I don't trust Li-Ion packs like the magicshine ones 2p2s. So I will probably put them in a box, that I can open to loud them and attach the endcups two the front of the box, with a little space for air-ventilation.

    But first I need your help:

    1. Is it right to wire the X-MLs serial? I think if I put them in parallel it could be that not every led get's the same voltage which would make a big difference in the light output from what I understand.

    2. I need battery power for 2 hours on low and 1 hour on high. If I put three 18650, 2.5Ah Li-Ion batteries serial, I have a "battery pack" with 3x3.7V=11.1V nominal (from full 12.6 to 9 V when nearly flat). With four batteries I get 4x3.7V=14.8V.

    3. The leds have a voltage drop of about 3.5 V each? Am I right in assuming that those sum up in serial, so 3 x 3.5V = 10.5V. That means I need a buck driver ? What I really don't understand: Can the buck driver H6Flex from maskled deliver 6 A out of four 18650 batteries serial without breaking them? I would be prepared to try to get 3A out of a 2.5Ah battery - but more?

    Thank you for your help

    PS This is also my first try in texting in a forum - so for the fun of it I try also one of these smilies

    Mr Radlos

  2. #2
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    Welcome to the forums!

    If I understand correctly, you plan to use 3 XM-Ls? If your requirement is 1500lumen on max, then 2 would be enough.

    1) Serial would be my choice. Otherwise I don't think you would find a driver that could deliver enough current. Edit: I see that H6flex can give up to 6A...

    2) See 3)

    3) Assuming 3,5V drop per led @ 3A, each led will use 10,5W on max, and give a little below 1000 lumen (check the datasheet for exact figures). So 2 LEDs give a little below 2000 lumen.
    2 LEDs => 21W.
    3 LEDs => 31,5W.
    Assuming that you use 2 LEDs, 2 hours on max gives:
    21W x 2hours = 42 Wh
    So: Your batteries must be able to give 42Wh, minus any driver losses etc (85% for arguments sake).

    One 18650 2,5Ah battery gives: 3,7V x 2,5Ah = 9,25Wh
    42Wh/9,25Wh = 4,54.
    Taking driver efficiency into account: 4,54/0,85 = 5,34 ~ 6 batteries.
    Exact runtime of 6 batteries is then, incl 85% driver loss: (6 x 9,25Wh x 0,85)/21W = 2,25hrs ~ 2hrs and 15min.
    => Then a 3S2P pack would be perfect.

    I believe that the H6flex driver would be a good match to use with a 3SxxP battery pack and two XM-L LEDs

    Hope this was understandable...
    Last edited by langen; 12-08-2010 at 05:43 AM.

  3. #3
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    Thank you langen for your answer

    I see now how I could calculate this. 6 batteries are too big for my bar light.

    I need 1 hour of 1500 lumens, that I could get from 2 or 3 X-ML:
    2 x 3.4V x 2.2A (750 lumen each) =15W
    3 x 3.2V x 1.4A (500 lumen each) =13.5W

    and 2 hours of say 300 lumens (low):
    2 x 2.8V x 0.35A (150 lumen each) = 2W
    3 x 2.7V x 0.3A (100 lumen each) = 2.5W

    I got these mesurements from here http://www.candlepowerforums.com/vb/...28#post3604728
    The 3 leds would probably be more efficient in low mode as well, my guess must be wrong. Let's just say in low mode 3W is suffient.

    1 hour of 15W and 2 of 3 W leaves me with 21 Wh.
    21Wh / 9.25Wh=2.3
    Taking driver efficiency into account: 2.3/0.85 = 2.7 ~ 3 batteries

    So I presume for capcity reasen I could use 3 batteries. But again my question can I really get 5A out of three 18650 an not breaking them? Is it better to use them as 3S1P or 4S1P?

  4. #4
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    I'd probably do 2 xm-l T6 with h6flex at a 2.0A current giving you

    2 x 3.37 x 2A = ~13.5W/H and 1400 rated lumen
    2 x 2.90 x .45A(L3 Table) = ~2.6W/H and 400 rated Lumen

    Series on 3 batteries

    3 xm-l would need at least 4 batteries in series after taking into account the +1v to stay above forward voltage and remain in regulation.

  5. #5
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    Well, 1500 lumens is nice, but the XM-L is a big LED, thus it will be floody. I would recommend adding XP-E for throw.
    CNC LED light housing for DIY projects

  6. #6
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    Quote Originally Posted by zemike
    Well, 1500 lumens is nice, but the XM-L is a big LED, thus it will be floody.
    Why everybody vote against "floody" lights?

  7. #7
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    Quote Originally Posted by klynk
    Why everybody vote against "floody" lights?
    A little flood is needed. Too much is just wasted light and to me, distracting. Everyone has their preferences though.

  8. #8
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    For my bar light I would like a lot of flood. The P7 torch I use now has a too distinguished hot spot. After riding for half an hour I keep seeing a white spot - I read others call it night blindness. It probably also has to do with the color of the light.
    So I wish my bar light to be an even flood, on the helmet I will ad a spottier torch (my direct drive MC-E torch is quite nice). I will consider 2x XM-L and 1x XP-E in series with 4 18650 in series.

    What I still don't understand is how the 18650 can provide 4A or 5A. Or is it the driver that somehow converts the higher voltages and low amperes in lower voltages and higher amperes???

    zemike: do you still sell 18650 battery holders? Your posted link doesn't work.

  9. #9
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    Single 18650 2500 mAh battery provides 2,5A current at 1C discharge rate, so 2C discharge rate provides 5A of current. Bleeding 18650 at 2C is still safe I think. About the driver, you're pretty much right.

  10. #10
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    Quote Originally Posted by mrradlos
    What I still don't understand is how the 18650 can provide 4A or 5A. Or is it the driver that somehow converts the higher voltages and low amperes in lower voltages and higher amperes???
    Some batteries for radio-controlled cars, planes etc can supply 10's of Ampere in short bursts, so without being a battery expert, I believe the max discharge rate has everything to do with the construction and chemistry of the battery.

    Regarding the driver:
    A buck driver will reduce the voltage and increase the currect from the battery, and vice versa for a boost driver.

  11. #11
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    You're not pulling 4 or 5 amps from a single cell, you're pulling a little over 2.2A a hour at 6.74v spread across 3 or more cells. Assuming the 2 xm-l setup is being used.

  12. #12
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    Quote Originally Posted by kan3
    You're not pulling 4 or 5 amps from a single cell, you're pulling a little over 2.2A a hour at 6.74v spread across 3 or more cells. Assuming the 2 xm-l setup is being used.
    As I understand it with the 2 XM-L I would pull 2 x 2.2A = 4.4A ? From what you say none of the batteries will suffer that 4.4A current as it is spread equally among the batteries in series?

    I just read, that the driver can only be put on 5A, so that would give me a bit more light but shorter run time on high.

  13. #13
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    Quote Originally Posted by mrradlos
    As I understand it with the 2 XM-L I would pull 2 x 2.2A = 4.4A ? From what you say none of the batteries will suffer that 4.4A current as it is spread equally among the batteries in series?

    I just read, that the driver can only be put on 5A, so that would give me a bit more light but shorter run time on high.

    The LED will be wired in series which means that the current requirement is the same but the voltage requirement will double. If you were to wire the LED in parallel the voltage would stay the same but the current requirement would double.

    2 xm-l @2.2A is:

    Parallel - 3.37v X 4.4A = 14.83W/H
    Series - 6.74v X 2.2A = 14.83W/H

    Assuming 1 cell is 3.7v and 2.5A then you get 9.25W/H per battery. That comes out to 1.87 hours of run time in a perfect scenario. The h6flex can output at 1.4A/2A/2.8A/3A/3.6A/5A/5.6A/6A/6.6A. It also needs 7v input if you're running more than the 1.4A output. Which means if you want to run just 3 batteries than series wiring is your best option.

  14. #14
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    The LED will be wired in series which means that the current requirement is the same but the voltage requirement will double. If you were to wire the LED in parallel the voltage would stay the same but the current requirement would double.
    AHHHHHHHH!!! I allways got that wrong!

    Thank you kan3. But then I need a driver that can produce 300mA (low, 300 lumen), 1.5A (high, 1'500 lumen) and 2.8A or 3A (show off, blinding) with my 3 XM-L. Would this driver http://www.lck-led.com/p501/Constant...6d8248ba0733dd or this http://www.candlepowerforums.com/vb/...Buck-Converter or this http://www.taskled.com/hipflex.html work with 4S1P and 3XM-L?

  15. #15
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    The Hipflex isn't made anymore, the h6flex does the same thing and more.

    If you look at this page you will see the current tables for the h6flex: http://taskled.com/techh6flex.html

    You can set the low and medium values for any of the first 4 values on that column of the chart. So for the 2.8A column you could set low to 1.593A or 50mA and same with the medium. Then you simply click between them to go to low - med - high - back to low.
    Last edited by kan3; 12-10-2010 at 09:09 AM.

  16. #16
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    Yes I so that, but I also read this on that page :

    Below 1000mA the h6Flex now transitions to PWM (at a nominal 400Hz) to provide dimming as recommended by Luminus. This means that, e.g. the 50mA L1 level is actually 1000mA pulses with a 1 in 20 duty cycle at 400Hz (1000mA/20 = 50mA average current to the load).
    From what I understand, I not able to use the high efficiency of the XM-L under 1000mA any mor with that driver?

  17. #17
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    Quote Originally Posted by mrradlos
    Yes I so that, but I also read this on that page :



    From what I understand, I not able to use the high efficiency of the XM-L under 1000mA any mor with that driver?
    I guess it depends on how you look at it. The XM-L is only around 3-4% more efficient than a XP-G at 350ma but it is closer to 9-10% more efficient at 1A.

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