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  1. #1
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    Need help finding the right XML driver

    I was reluctant to post this call for help because I thought that the answer would be easy to find. However, after looking high and low, I can't seem to find a good solution.

    I want to do a 2 XM-L setup, and I want to drive them somewhere between 1200ma and 1600ma. Also if possible, I'd like to buck down instead of boosting up so that my setup can be interchangeable with my existing batteries and lights.

    So, the easy answer that would definitely work is the b3 (b3Flex Product Description). However, I'm thinking that there has to be a cheap driver out there among the many $5 non-configurable boards. (Like this one T6 3-Mode Regulated LED Driver Circuit Board for DIY Flashlight (2500~3000mA 4.5~18V) - Free Shipping - DealExtreme).

    Any ideas? Am I just asking for too much? Do I need to just spend the bucks on the b3?

    In case you are wondering, I used these calculations (see link) to settle on 2 instead of 1 XM-Ls. The housing type that I want to use dictates 2 instead of 3 LEDs.
    https://docs.google.com/file/d/0B-u2...FzbHV2aTQ/edit

    A 3 LED setup would give me my ideal balance of light, heat and battery life at 1000ma, but unfortunately, I'm really looking for the 2 LED housing.

    Any help would be greatly appreciated.

  2. #2
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    The housing type that I want to use dictates 2 instead of 3 LEDs.
    https://docs.google.com/file/d/0B-u2...FzbHV2aTQ/edit
    Can't seem to open the Google doc you're referencing in order to see the housing. Do you have to change the permissions?

  3. #3
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    Quote Originally Posted by ThinkBike View Post
    Can't seem to open the Google doc you're referencing in order to see the housing. Do you have to change the permissions?
    Oh, sorry about that. The document isn't for the housing, it's for my calculations of light output and power consumption. It's based on info I got from the XM-L data sheet. I have the doc set to share now.



    Since you asked, here is the housing style that I'm planning on using. This is an old light I built with SSC P4 LEDs. I use it for road riding, but I like more light for off-road riding. I'm thinking 2 XM-ls will more than do.

    From Bike light


    I want to stick with this housing because it is super easy for me to build, all the parts are readily available, and the only power tool required is a drill. (Though a Dremel saves time.) I'm not quite ready for the lathe. I was going to do something with pucked up's Very Easy XML light that is generating so much discussion, but I can't easily get the right parts.

  4. #4
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    [edit] ... from your calcs. .....
    3 x XM-L @ 1A for 2 hours on 2 cells ?
    what size/capacity are these cells ?
    ...Scun.thorpe, UK

  5. #5
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    Quote Originally Posted by HEY HEY ITS HENDO View Post
    [edit] ... from your calcs. .....
    3 x XM-L @ 1A for 2 hours on 2 cells ?
    what size/capacity are these cells ?
    Let me know if my math is off. According to the cut sheet, these LEDs run about 3.0 volts when driven at 1A. That's 3 watts. 3 LEDs is 9 watts.

    The cells are 3.7v 2500ma. This should be about 9.25 watts per cell or 18.5 for 2.

    Is my logic or math off?

  6. #6
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    in the real world batteries never, ever, live up to their claimed capacity!,
    then you have driver loss, Voltage sag, ......
    [edit] usually the claimed capacity is based on 4.2v.>2.5v @ 0.2C discharge
    ...Scun.thorpe, UK

  7. #7
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    Quote Originally Posted by HEY HEY ITS HENDO View Post
    in the real world batteries never, ever, live up to their claimed capacity!,
    then you have driver loss, Voltage sag, ......
    So as I sit here and think about what current to use for driving the lights, what margin should I use for the false claims, driver, etc.? Will these factors really have me extremely far off? Is there a better way to plan?

    I did figure that they would be off some, certainly at the very least as the batteries age, and that the driver would consume some. I am planning my build with a time buffer over what I usually need. I just don't know by how much. The wild eyed expression makes me think that I might be off by a lot. I figured I would be somewhat close without accounting for the driver and other factors.

  8. #8
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    ok, 2 x XM-L on a buck driver @ 1.6A,
    you will need 3 cell series (3S) or 4 cell series (4S)
    to account for driver voltage overhead, voltage sag, runtime
    ...Scun.thorpe, UK

  9. #9
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    Thanks for setting me straight. I'll keep mulling it over. I've never thought about wiring in parallel and using a boost driver, but maybe that's an option?

  10. #10
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    indeed it is, but check out the Lflex linear driver
    2 cells in parallel (2P) or 3 (3P) for extra runtime......
    ...Scun.thorpe, UK

  11. #11
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    Exactly what brand / capacity battery are you using? Are these new batteries?

  12. #12
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    Quote Originally Posted by ThinkBike View Post
    Exactly what brand / capacity battery are you using? Are these new batteries?
    TrustFire Protected 18650 Lithium Battery (2500mAh 2-Pack Blue) - Free Shipping - DealExtreme

  13. #13
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    The cheapest and simplest driver which is at the lower end of your requirements is this 1.25A 3V-18V single mode driver from DX:

    18V 5W Cree Circuit Board for Flashlights (16.8mm*5.5mm) - Free Shipping - DealExtreme

    I have successfully used this driver is several of my XP-G lights (see links below my signature) that I have built for myself and friends and they have been totally reliable. The other thing I like about them is that they are 17mm diameter as opposed to 25mm for a bFlex, so easy to fit into a small light.

    You would easily get 2+ hours run time from a 2S 2500mAh battery pack and obviously double that from a 4-cell either 2S2P or 4S.

    There are several other multi-mode torch drivers from DX and KD that you might find give you the higher drive current you are looking for such as this one:

    21.65mm 8.4V 1500mA Circuit Board for Bike Light SKU 94182 / 82510 / 82734 + More - Worldwide Free Shipping - DX

    but I havenít used any of those so canít comment one way or another.

  14. #14
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    Quote Originally Posted by HEY HEY ITS HENDO View Post
    indeed it is, but check out the Lflex linear driver
    2 cells in parallel (2P) or 3 (3P) for extra runtime......
    This is getting to be very educational. So what presents an upper limit to the number of batteries when running parallel? Could I also run 4P or 6P? Also, are there any downsides to running parallel that I should consider. I notice that most consumer devices (including lights) use batteries in series. Is there some limitation or issue with running a parallel setup that makes series wiring more attractive?

  15. #15
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    With what you are contemplating i.e. two XM-Ls in series, the LFlex isít really a suitable driver. It is linear driver designed to work with one XM-L to one 3.7V cell. Please read the TaskLED product documentation for clarification on this:

    LFlex Product Information

    The b3Flex is the one you should really go for if you are considering a TaskLED driver

    For two XM-Ls in series you with need a battery pack with at least two 3.7V LiIon cells in series. 2, 4, or 6 etc. in parallel will not give you enough voltage because parallel battery packs double the available current but not the voltage.

    You can increase the run time of your pack by doubling up the cells and either configure them as follows:-

    2S2P = 7.4V 5000 mAh
    4S = 14.8V 2500 mAh

    Note you will only be able to use the 4S pack with a driver that is capable of handling 17V or over such as the first DX one I suggested or the b3Flex.

    EDIT: I should have added a caveat. If you run the XM-Ls in parallel then you could use the LFlex with a 2P or 4P battery pack. You would need to double up the drive current in this case because each XM-L would only see half the current. I don't know how advisable this would be as I have never tried it but others who maybe have might be able help.
    Last edited by OverTheHill; 12-03-2012 at 04:15 AM.

  16. #16
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    Quote Originally Posted by OverTheHill View Post
    If you run the XM-Ls in parallel then you could use the LFlex with a 2P or 4P battery pack. You would need to double up the drive current in this case because each XM-L would only see half the current. I don't know how advisable this would be as I have never tried it but others who maybe have might be able help.
    I'm glad you mentioned this. I had not considered wiring the LEDs in parallel. I have a driver on hand that would give me a good power if I ran the LEDs in parallel.
    T6 3-Mode Regulated LED Driver Circuit Board for DIY Flashlight (2500~3000mA 4.5~18V) - Free Shipping - DealExtreme

    Any downside to doing this? I know that normally you might have an issue with sending too much current to a single LED if the connection to the other one fails. However, in this case, since a single XM-L can handle the full current of the driver that shouldn't be an issue. Any other reason I shouldn't try this?

  17. #17
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    Quote Originally Posted by redbeans View Post
    I'm glad you mentioned this. I had not considered wiring the LEDs in parallel. I have a driver on hand that would give me a good power if I ran the LEDs in parallel.
    T6 3-Mode Regulated LED Driver Circuit Board for DIY Flashlight (2500~3000mA 4.5~18V) - Free Shipping - DealExtreme

    Any downside to doing this? I know that normally you might have an issue with sending too much current to a single LED if the connection to the other one fails. However, in this case, since a single XM-L can handle the full current of the driver that shouldn't be an issue. Any other reason I shouldn't try this?
    Not that I can see, in fact marpilli is doing exactly this in his current CatEye Doubleshot XM-L thread.

  18. #18
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    Thanks. I'll see if I can find the thread.

  19. #19
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    Thanks a lot! I checked out that thread and I found it helpful. I thought marpilli's battery thread was helpful too.

    (Here are links to both of the threads for anyone that ends up reading this thread later...)

    CatEye Double Shot XM-L (U2-1C) Upgrade

    DX Charger Modification & Battery Pack Builds

    It looks like I could really gain a lot of flexibility and options if I go with a boost setup running all my batteries in parallel. I'm going to see what different drivers will fit my needs and maybe do some sampling.

    Thanks again for the help!

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