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  1. #1
    relax
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    MaxFlex setting...

    I am going to get a "Cutter MR11 kit Q5 & Max flex" to put in my home build housing. I want to use some NiMH 6volt 4a/h batteries. What would be the minimum voltage setting I should use?

    Cheers,

    J

  2. #2
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    I have my min voltage set at 5.5 volts on the light that uses 6 volt Ni MH batteries

    I saw a graph somewhere that showed that NiMH cells start with quite a high initial out put (1.7 volts I measure mine at freshly charged), drop quite quickly to 1.2 volts and run as a flat line for most of their 'life' then as it starts to drop off it again goes quite quickly. Working on 1.1 volts per cell was recommended to me (6 volt NiMH batteries have 5 cells) and seems to be doing the job. I haven't tested to failure yet exactly how long I have from the moment it starts to warn me to actual lights off though

  3. #3
    relax
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    Thanks iggs,

    I'm going to try 5.5 volts as well.

    J

  4. #4
    Homer
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    Quote Originally Posted by jeep
    Thanks iggs,

    I'm going to try 5.5 volts as well.

    J
    1V per cell is a pretty safe number, so 5V should work.
    You cán go lower, but with that number of batteries in series you dont know if they are all discharging to the same voltage.
    And with that battery and a triple XR-E setup your are pushing the batteries pretty (!!) hard. You probably won't get anywhere near the rated (theoretical) capacity.
    [SIZE=1]Need optics for DIY bike lights? [/SIZE][SIZE=1][/SIZE]

  5. #5
    relax
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    Could I use a 9.6v NiMH battery or is it to close to the forward voltage of the triple Cree?

    And set the minimum voltage at 8 volts on the Maxflex?

    J

  6. #6
    Singletrack Daydreamer
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    I don't know the MaxFlex that well (nobody does, as it's a newer product) but generally, the closer to your voltage forward, the more efficient the circuit will operate.
    Train 'til you puke. Cheat to win. Party like a rockstar. We miss you, Jan!

  7. #7
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    Because its a boost driver if the voltage goes over the forward voltage that the led's are drawing the driver will pull itself out of the equation. So this is a battery question, while the cells are rated at 1.2 volts at full charge they can be a bit more, I've seen them at 1.7 volts for instance, this would give an 8 cell pack an initial, full charge, voltage of 13.6 volts which would be too much. Not sure what damage it may or may not do.

    When it comes to the low battery setting it depends how much notice you want, do you want a just before they go or a warning that gives you a bit of time to 'know that your batteries are starting to run down and to do something about it'

    I need to do some run tests on mine to see how much time a couple of different settings gives me

  8. #8
    relax
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    Usually after charging the NiMh battery pack they have like 15 to 20% more voltage than they are rated.
    But if I measure the battery pack on load it's only about 6 to 8%.
    From what I understand the voltage reading should be done under load, but I not sure.

    Could someone tell me what the exact forward voltage of the "triple Q5 & Maxflex" is?

    Thanks,

    J

  9. #9
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    Quote Originally Posted by jeep
    Usually after charging the NiMh battery pack they have like 15 to 20% more voltage than they are rated.
    But if I measure the battery pack on load it's only about 6 to 8%.
    From what I understand the voltage reading should be done under load, but I not sure.

    Could someone tell me what the exact forward voltage of the "triple Q5 & Maxflex" is?

    Thanks,

    J
    You are correct...measure the battery voltage under load. That is what the load will see.
    NiMH cells are 1.2 Volts each under load and do read higher when they aren't connected. Your “6 to 8 %” may be an error with your meter.

  10. #10
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    Quote Originally Posted by jeep
    Could someone tell me what the exact forward voltage of the "triple Q5 & Maxflex" is?
    Now I'm not sure on this but this is what I've worked out

    The forward voltage is all about the draw of the LED's. This will depend on what mA's the led's are running at. I think the Q5 running at 1000mA typically runs at 3.7 volts each.

    On the taskled website http://taskled.com/techmaxflex.html there is a table showing varying levels of efficiency, between 84% and 91%, George reckons on doing calculations based on 88%

    so
    here's an example, I'll use my build as an example

    Vf for the Cree's is 3.3 @ 350mA, 3.5 @ 700mA and 3.7 @ 1000mA

    So @ 700mA it workes out at 3 x 3.5Vf x 0.7A = 7.35watts

    + 12% inefficeency through the driver = 7.35 + 15%(0.882watts) = 8.232 watts being used in total

    If I'm using a 7.2 volt battery that means its drawing 8.232watts / 7.2volts = 1.143amps

    Data for voltages taken from here - http://www.cutter.com.au/proddetail.php?prod=cut651

    Hopefully I've got the maths right and that it a)makes sense and b)helps a bit.

    You should be able to find out any number you want from that lot for whatever battery and led combination you are thinking of using

    Ian


    Edited to change the calculation from 85% efficiency to 88% after reading the taskled website again
    Last edited by iggs; 11-26-2007 at 03:01 PM.

  11. #11
    relax
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    Thanks for all your info

    So, it's probably safer not to use a 9.6 volt battery then.

    My kit arrived today

    Now I have to adjust the housing and slowly put all the stuff together.

    Cheers,

    J

  12. #12
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    I'd contact cutter if I were you. I thought the entire point of buying a MaxFlex puck was that you could use voltages above your Vf and below your Vf because it was both a boost and regulating puck. Why else would they offer this instead of the Fatman alone?

    Talk to the experts who are actually going to be the ones to warranty the unit if something goes wrong.
    Train 'til you puke. Cheat to win. Party like a rockstar. We miss you, Jan!

  13. #13
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    Quote Originally Posted by rockymtnway
    I'd contact cutter if I were you. I thought the entire point of buying a MaxFlex puck was that you could use voltages above your Vf and below your Vf because it was both a boost and regulating puck. Why else would they offer this instead of the Fatman alone?

    Talk to the experts who are actually going to be the ones to warranty the unit if something goes wrong.
    Have a look here http://taskled.com/compare.html

    You'll see both the fatman and the maxflex are boost drivers. The difference is that the maxflex has a UI in the same way as the bflex does.

  14. #14
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    Ok, so in the time it took me to write my post (along with interruptions) iggs answered the question more concisely...

  15. #15
    Singletrack Daydreamer
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    Thanks for the clarification. I must have misread some of the literature on the Cutter site. I've been using BuckPucks for so long that I'm only now coming up to speed on these Taskled pucks. Since I have a variety of 14.8v batteries, I've never been that concerned with boost pucks, but now that I'm upgrading a friends MR11 with a 7.2v battery, I've been trying to do my homework.

    Thanks again!
    Train 'til you puke. Cheat to win. Party like a rockstar. We miss you, Jan!

  16. #16
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    for the taskled drivers its worth using the taskled.com website. The forum also has useful info. Cutter are a distributer of the taskled products

  17. #17
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    I think I also got a bit sidetracked by this post by Mark at Cutter.
    Train 'til you puke. Cheat to win. Party like a rockstar. We miss you, Jan!

  18. #18
    relax
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    Maxflex = boost driver.

    Got my home made light housing + MR11 Cutter kit Maxflex + 6 volt NiMH finished and it seems to be working fine.
    Now I have to water proof the unit and I am done.
    I still have to test the unit in the bush and on the bike, it seems very promising.
    With the maxflex you can run the LEDs at 1200ma, its blinding .


    J

  19. #19
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    Knew I'd seen this somewhere

    This graph shows the 'normal' discharge curve of a NiMH battery



    Its from http://component-shop.co.uk/html/bat...explained.html

    As the graph shows the batteries have a pretty consistant voltage for their useful life and die quite quickly at the end. I set my maxflex firmware based on this and other peoples advice at 1.1 volt per cell so that I have some get out of jail warning from the light that the battery is going and that I need to do something about it

    Hope this helps

    Ian

  20. #20
    relax
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    There is also some good info on Ni-MH batteries on this link:

    http://www.duracell.com/oem/Pdf/others/TECHBULL.pdf

    J

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