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  1. #1
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    New question here. LED newbee questions

    Hi!
    I want to build the simplest and cheapest triple LED headlamp possible. I already have a MR11 optic from Cutter, 3 CREE X-RE P5 LEDs, an old flashlight and a welding iron... I want to wire my 3 LEDs in series and give them about 750ma. I want to know 2 things.

    First, what is the best, cheapest and simplest driver that i should use. I would like to have a + and - entry for the batteries and a + and - for the LEDs. On and off would be operated by a simple on/off switch, no dimming.

    Second question, from what I read, I need 10.5V (LEDs) + 2V (driver)to drive my system and 2200ma. If I have a lower or higher voltage battery or a higher/lower amperage battery setup, what would be the consequences on my system?

    And also, what are the main differences between a Buckpuck and a bflex style driver/PCB.

    Any help would be greatly appreciated, the snow shoe season here in Quebec as begun (1.6m of snow on the ground) and I would like to test my light soon!

  2. #2
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    Eeeeee... Anybody.... Please.....


  3. #3
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    A buckpuck (or any driver with "buck" in it's name) is designed to take power from a battery and output it at a fixed current at a lower voltage than the input voltage. e.g. a 750mA buck driver might be rated at 12-18V input, and would output 750mA at any voltage up to 2V less than the input voltage (just a theoretical example, not based on real specs). So whether you ran 1 LED or three in series, it would still output 750mA to the LED.

    Conversely, a boost driver would require a lower input voltage than the output voltage (and would draw current from the battery at a higher rate to get the extra power)

    A bFlex style of driver is like a buck in that it requires a higher input voltage than the forward voltage of the LEDs that you are driving. The advantage is that it is programmable so you can set multiple brightness levels selectable by a clicky switch, an have things like a flashing mode. There is also the maxFlex which has the same output modes but can be either buck or boost, giving you flexibility over what batteries you run.

    The bFlex is great for cycling as you can select your brightness to match the speed and terrain. If you just want it for snow shoeing that might not be so important to you, but conversely you don't want to be blinded by the snow, and in the dark under the trees so flexibility is always good!

    Your battery will be rated by voltage (depends on he number of cells in series used to construct it), storage capacity (in mAH, i.e. the number of hours it can discharge at a specified current) and the maximum discharge rate. A 2200mAH battery might be rated to last 2.2 hours at a current of 1A (1000mA). Running the battery at a lower current usually lets you draw a greater total amount of power, e.g. the same battery drawn at 200mA might give you 2500mAH.

    For power to weight, and cold weather performance, you will be best off going with a Lithium Ion batttery. From there on you need to choose your battery and driver circuit in combination, e.g. a 7.2V battery (2 cells in series) with a boost driver, or a 14.4V battery (4 cells in series) with a buck driver or bFlex. Choose the size of the battery by how long you want the light to burn. If you only do short hikes then you can get away with a smaller battery pack and boost driver. If you go out for longer you can get higher efficiency with a higher voltage battery pack, drawn at a low discharge rate by a buck driver.

    As far as building, you have probably read the myriad threads that stress the importance of heat sinking. You want the LED mounting to have a good thermally conductive path to the outside of your housing. Even if it is freeezing outside, if the heat from the LEDs doesn't make it to the outside of the housing they will fry (and lose their brightness and efficiency).

    Hope this answers your questions
    Dylan (in Sydney Australia where there is no snow at all today!)

  4. #4
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    That's an answer!!!!

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