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One Battery to power them all?

Discussion in 'Power Electronics' started by landrus, Nov 2, 2010.

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  1. landrus

    landrus

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    Nov 2, 2010
    I have a 14Wh 12V Lithium battery that I am using to power a homemade 12v 20w headlight for my bike. It's a low rider 3 wheel recumbent and for some reason that headlight is not enough to alert joggers that something is coming in their direction. I theorize that they tune out white lights since the path is along a busy road. So, I bought some green LEDs from superbrightleds (10 B-G, rated at 12vdc and 19ma on their site).
    I want to run them off the same battery but if I put them in parallel to the headlight I'm going to have to add resisters to each LED to balance with the headlight. Battery killer for sure, I'm thinking. There has to be something more elegant. Any suggestions?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Use white LEDs instead of a lamp, and flash them.
     
  3. Resqueline

    Resqueline

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    Jul 31, 2009
    10 B-G tells me nothing and gets me nothing on their site, but if your data is correct then you just hook them up to the battery like any other lamps. Balancing what?
    If anything is going to kill your battery it's that 20W headlamp.. ;)
     
  4. landrus

    landrus

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    Nov 2, 2010
    Thanks, I'll give it a try. The balance idea comes from looking up parallel led circuits using different color leds. I assumed that since they required different resistors to balance the drops that would be the case here too. Won't hurt to try it though.
    The flashing white leds was a good suggestion too. I'm looking into circuits to do that as well.
     
  5. Resqueline

    Resqueline

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    Jul 31, 2009
    I see what you meant, but since those LED's are rated at 12V they already incorporate a resistor so there's no need for anything more. Flashing LED's is a very good idea.
     
  6. landrus

    landrus

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    Nov 2, 2010
    I get it now. Thanks. I made the headlight and the lamp was only $3 so swapping it out for an LED equivalent wouldn't be a problem. How would you flash it? 555 timer?
    The added bonus of going to led means less draw on the battery which means I can add a small 12vdc 90ma fan to blow across my face shield to keep it from fogging. I ride all year and 20 degree mornings are too raw riding along the river with a head wind.
    Another option would be some kind of heater wire or tape. Would only need a small area possibly mounted on a face shield with silicon. Know any sources for something like that?
    Think I have an old hair dryer I can scrap for the nichrome wire.
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    Your halogen lamp has a guesstimated efficiency of 15 lumens/W. Cheap LED's have around 30 lm/W and the best (more expensive) ones have around 100 lm/W.
    Self-flashing LED's exists, but lacking that a 555 circuit should do the trick. Diagrams for using both should abound on the net.
    I've observed fogging on the backside of the windshield in open cars. The reduced pressure and the lack of airflow there promotes this.
    A fan might help, but probably even more so a directed airflow from the front going up across the backside of the windshield.
    I don't quite see heating as an option running on batteries, but if all else fails why not try. How about using/directing the waste heat (air) from the lamp to the windscreen?
    You'd want a much thinner wire than found in a hair dryer anyway but I can't think of any sources right now.
     
  8. landrus

    landrus

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    Nov 2, 2010
    thanks again for your thoughts. I agree with intake at the bottom of the sheild and the exhaust at the top. I found some dual lens safety goggles that have a large surface at the top so I will try putting the small fan mounted on the top with intake ports at the bottom and see how that works.
    I also found some flat nichrome ribbon that sells for a couple bucks a foot that I'm going to try to sandwich between two lenses and drive with the 12v battery. The space that needs to remain clear is really very small so I'm hoping that by heating space between the lenses, that the inner lense will stay warm enough to not condense the moisture from my face and breathe. I gather from your post that the thinner the ribbon the better, if I'm going to get any usable heat at low enough draw on the battery. Is that correct?
     
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