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correct resistor help

Discussion in 'General Electronics Discussion' started by gizmo13, May 12, 2011.

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  1. gizmo13

    gizmo13

    2
    0
    Apr 20, 2010
    Hello all,

    I am making a chaser light unit for my car and I am planning on using a 3w led.
    I have used a website called ledz.com which has an automatic resistor calculator.
    I typed all the info: 14v, 2.2 voltage drop with 700 mA and it gave me a resistance
    calculation of 16/857 ohms.
    Is this correct??????


    Craig
     
  2. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    The formula is R=E/I = (14-2.2)/0.700 = 16.857142
     
  3. nbw

    nbw

    48
    2
    May 8, 2011
    Just be aware that if your battery voltage is down a bit; e.g. you have lights on, or the battery is just getting old - you won't be seeing 14.4V but a little less. Might also be worth considering some form of protection in case the odd higher voltage spike comes through...!
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Hopefully, the calculator also told you that the resistor will dissapate 8 Watts. It's going to get hot, and if you use less than a 10W resistor, it's going to melt.

    Bob
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    Using a resistor to drive a high powered LED is generally not the best idea. You are far better off finding a constant current driver, and preferably a switchmode device so that you can get high efficiency as well as constant brightness as the voltage fluctuates.
     
  6. gizmo13

    gizmo13

    2
    0
    Apr 20, 2010
    Thanks all.
    Will do some more research.


    Craig
     
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