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  1. #1
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    what battery are you running with your tripple cree

    Im looking for a battery for my new light and I was wondering what other people are running for AH. I will be running the Bflex driver with three R2 LEDs. I was thinking about using 2 14.8v 2000mah batteries, but I am confused about my run time. I was thinking it will be around 2 hours a battery on the highest setting is that correct?

  2. #2
    Thirsty
    Reputation: BrewMaster's Avatar
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    Here's a good one that I just bought.

    http://www.all-battery.com/index.asp...OD&ProdID=1149

  3. #3
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    what kind of run time are you expecting with that battery? It looks nice I like that the conector is already on it.

  4. #4
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    Forward voltage seems to become a bit higher with the better rated Cree's so let's assume it is 3.7V at 1A then your power consumption is:
    3.7V * 1A * 3 = 11,1 Watt, then driver efficiency:
    11,1W / 0,9 = 12,3 Watt

    Next calculate the power in the battery:
    14.4V * 2Ah = 28,8 Wh

    So the runtime will be:
    28,8Wh / 12,3W = 2,34 hours

    When you'd want a longer runtime a battery with better capacity (2400 mAh instead of 2000) would give you almost 30 extra minutes with the same size batterypack. When that isn't enough I would suggest to lower the drive current to 700-800 mA, the difference in light output will be quite small. Your runtime will be @700 mA more then 4 hours.

  5. #5
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    I have three different tripple builds, Cree Q4, Seoul P4 U, Luxeon K2. All using the bFlex drivers. I have a 14.8v 4800mA pack that works with all three lights for well over 5 hours of burn time tested. I have a 11.1v 5200mA Li-Ion pack that will work with the Seoul and Luxeon lights but not the Cree. The peak volts (12.6v) from full charge allow it to work and I've tested it for over 6 hours of run time. I don't get the reason why it won't run the Cree. Maybe at 1000mA drive current the Vfs of the Cree's are higher, I haven't done any meter checks. So I guess what I'm trying to say is it's a crap shoot whether or not the 11.1v pack will work. Maybe if I lower the drive current to 700 or 800mA it would work. The light still comes on plenty bright but you can tell the driver isn't working.

  6. #6
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    sweet thanks for the help, it seems that the 2 small batteries will work perfect for me as I can probably get by on our average ride with only one of them and save weight or I can plug in both and have a longer burn time. Thanks for the help. Man I cant wait to get this thing finished, one more quick question... is it safe to test my light with a car battery? I cant see a reason why it wouldnt be but I want to be safe. Thanks

    Steve

  7. #7
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    mofoki,
    Your 11.1V battery pack probably isn't working because you don't have enough voltage differential between LEDs and battery. The Crees (run at 1000mA) are in the 3.7V range, making the total voltage right at 11.1. The bFlex driver needs (supposedly) 1.5V more than the Vf of the LEDs. So that means that with the Crees you need 12.6V at the battery. My guess is that the numbers are slightly different in real life, and that the Seoul and Luxeon LEDs have a slightly lower Vf than the Crees. Meaning that the Vf of the Crees is BARELY above the threshold needed for the bFlex.

    I'm using a Fatman driver instead of the bFlex (for now) and am running a Sony InfoLithium camcorder battery (the small one) on my pack. So far its working great for my 35 min commute (each way) meaning that I'm getting just over 1 hr out of a total charge.
    If it works well for a while, I plan on getting one of the big packs to use instead, (4.8Ah instead of 1.1Ah).

    I'm also planning on setting up another triple Cree using a bFlex. I purchased a water bottle 14.4V 5Ah NiMh pack from batteryspace to use with my pond scum setup last year, and plan to power the second light with it.

  8. #8
    Singletrack Daydreamer
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    If you have a dimmable light or plan to run it at only 700ma, then runtimes will be significantly longer. I have accumulated numerous 14.8v Li-ion batteries since my HID days, so I now have 4.8ah, 4.0ah, 2.4ah and 1.4ah. Before I built a successful LED homebrew, I bought a Night Lightning (3 SSC P4 bin U) and use the dimming feature all the time, going to the low beam anytime I was climbing, midbeam on the flats, but full high beam when descending. I never had a problem getting well over two hours out of the tiny 1.4ah battery. One ride I got just over three hours out of it.

    If you can dim, a 14.8v, 2.0ah battery should easily last four-plus hours in its first year. Just be aware, Li-ions lose roughly 10% of their capacity every year, so if you plan on using the battery in three years and plan on riding at the battery's limit, you may want to go up a size (to 2.4ah).
    Train 'til you puke. Cheat to win. Party like a rockstar. We miss you, Jan!

  9. #9
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    I understand the whole voltage drops in the circuit verses the power supply voltage required and I have all the spec sheets printed out for easy reference. The problem is the real life findings. It can be different depending on the emitters, the temperature, where the the emitters came from. I've learned that I can't build one of the systems and expect it to put out a predetermined amount of light based on specs. You need actual measured values. During the building phase I hook the LED's up to my regulated power suppy and see what they draw at different currents but even that changes once everything is in it's housing. So that's why I said it's a crap shoot. All you can do is try a battery pack, see if it works, if it doesn't get something different. I would prefer to use an 11.1v because of it's size and weight and capacity verses the 14.8v pack. If I have to use 14.8 volts then the lower capacity packs would be my next choice.

  10. #10
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    I kinda figured you knew what you were doing... but had to throw that out.

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