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Thread: how long will 18650 3100mah battery last on xml-t6 led?

  1. #1

    Default how long will 18650 3100mah battery last on xml-t6 led?

    I bought a light with a CREE XML T6, and i want to buy a Li-ion 18650 protected battery for it. I need it to last me at least 3 hours on High setting.

    I am planning on getting some Generic Batteries with Panasonic cells and 3100mAh capacity, wonder if they will last me 3 hours and how much more would i get out of the 3400mAh capacity? I've seen the 3100mAh for about $8/each shipped and for the 3400mAh is a little over $10/each shipped.

    Thanks

  2. #2

    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    An XM-L is an emitter. It does not determine its own drive current or the minimum battery operating voltage. Those parameters are set by the flashlight's driver.

    What is the light, exactly?

  3. #3

    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    Quote Originally Posted by torukmakto4 View Post
    An XM-L is an emitter. It does not determine its own drive current or the minimum battery operating voltage. Those parameters are set by the flashlight's driver.

    What is the light, exactly?
    don't know, is from ebay. says 1600 lumens, but i don't think they go up that high, i saw another listing for a similar one with 10 W LED, so I assume is one of those.

  4. #4
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    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    Assuming we're talking about a fully driven XM-L (ie 3A), you will NOT get three hours from a 3100mAH battery. You should expect more like an hour (plus or minus). You may have a lower mode which would allow the light to last three hours. But this would require that your current draw be only about one amp, which would only give you maybe 300-400 lumens.

  5. #5

    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    Quote Originally Posted by StorminMatt View Post
    Assuming we're talking about a fully driven XM-L (ie 3A), you will NOT get three hours from a 3100mAH battery. You should expect more like an hour (plus or minus). You may have a lower mode which would allow the light to last three hours. But this would require that your current draw be only about one amp, which would only give you maybe 300-400 lumens.
    What if it was a 3400mAh battery?


    Thanks

  6. #6
    Enlightened
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    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    It is only 9% difference between 3100mAh and the 3400mAh battery so don not expect it to be much better.

  7. #7
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    Your question is sort of like asking how many meals a big takeout plate of spaghetti will provide. Even with a weight of spaghetti, we don't know how quickly you eat it!

    Battery life is roughly equal to (Battery Capacity) / (Current Draw from Battery). We can make some ASSumptions about these "1600 lumen" lol-lights in general. I'd guess the actual current is somewhere between 1 to 1.5 amps, the actual lumens somewhere between 300 and 600, and the 'full output' to last about one minute before thermal droop happens. That gives us a wild-A**-guess of a runtime between two and four hours, depending on how loosely the manufacturer claims are made.

    An actual-1600-emitter-lumen output XM-L based flashlight would require considerable expensive architecture (Direct-soldered bare LED on massive copper block with five to six amp current) and have runtime of a few minutes per 'burst,' half an hour total.
    My biggest light-hog is my camera.

  8. #8
    Flashaholic* mattheww50's Avatar
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    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    Actually I doubt that 1600 lumens is even possible with an XM-L T6. That would probably require ~25 watts drive power. Unfortunately there is no mention of the flashlight involved, so we have no idea
    what high is , but realistic maximum output for an XM-L T6 is probably around 900 lumens. That would require ~12 watts, and would require extensive thermal management. A 3100mAh cell contains stores about 11 watt hours of energy. So if you if make some assumptions (which are admittedly, exactly that) we can 'thumbnail' the result.

    So lets say the output is about 750 lumens (and without very extensive thermal management that's probably close to the upper limit on an XM-L T6), that is going to require ~9 wats into a 'good' driver, so figure a little better than 1 hour run time for eash 3100 mAh 18650 cells in use. If you want 3 hours from a single 3100mAh 18650, the output going to have to be limited to something around 300 lumens.

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    Default Re: how long will 18650 3100mah battery last on xml-t6 led?

    This is very simple maths. 3100mAh. Call it 3000mAh for simplicity.
    3000mAh = 3Ah, = 3 Amps for 1 hour. Or 1 Amp for 3 hours.

    So if you want 3 hours from your 3Ah cell, you need to limit current draw to 1Amp. As matheww50 pointed out in previous post, that will be around 300 lumens max.

    There is a good chance you're "1600 Lumen" light is drawing somewehere between 2 and 3 amps so is putting out 500 - 900 lumens.
    A Malkoff Hound Dog will put out around 100 lumens continuously, but with 2 x 18650 3400mAh cells will last around 1 hour 45 minutes.

    Regarding the 3100mAh to 3400mAh run difference, that's also very simple. 300 is about 9% of 3100. 3100 + 300 = 3400. So 3400 will last around 9% longer than 3100mAh.

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