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l.e.d light

Discussion in 'LEDs and Optoelectronics' started by mogy, Apr 10, 2011.

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  1. mogy

    mogy

    7
    0
    Apr 10, 2011
    :rolleyes:i have a
    ' LED Number: 42
    Total light generated: 200 lumen
    LED Feature: wide view angle (120 degree)
    Emission color: blue (465-470nm), red (630nm)
    Color ratio: red LED/blue LED = 2:1
    Dimension: 18.9" x 0.4" (479 x 10mm)
    Power cord length: 10"
    Working voltage: 12V DC
    Power requirement: 2.5W
    and a 12v 7ah batery. How do i safely connect them together? i also have a 1300mah 12v nicd.
    :confused:any idea,s
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    2,809
    Jan 21, 2010
    Read this and then come back with any questions you have.
     
  3. mogy

    mogy

    7
    0
    Apr 10, 2011
    re. l.e.d

    i might be wrong,but, does that information suggest a current limiting resistor? (dyslexia)
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You might be right.

    Some form of current limiting is *essential*
     
  5. mogy

    mogy

    7
    0
    Apr 10, 2011
    any ideas? (12v 2.4 watt, 12v 7ah lead acid batery)
     
  6. mogy

    mogy

    7
    0
    Apr 10, 2011
    i looked at resistor calculator, (voltage drop defeated me!)
     
  7. mogy

    mogy

    7
    0
    Apr 10, 2011
    insperation:
    [​IMG]
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    If that is the device you are using, then it has resistors incorporated in it and can operate from a specified voltage.

    Otherwise, you need to determine the following:

    a) LED forward voltage drop (or sum of these if you connect several in series)
    b) LED current
    c) Power supply voltage

    Add from these calculate the series resistor value.

    (a) and (b) are typically specified for a device, often in terms of a graph showing one vs. the other. You will want to choose a LED current less than the maximum, and use this to determine the forward voltage drop.

    You have already told us that (c) is 12V

    If you don't have specs for the LEDs then there are some rough figures for forward voltage drop in the article I pointed you to.
     
  9. mogy

    mogy

    7
    0
    Apr 10, 2011
    yep i just checked, resistors already calculated, any joy for betwean unit and batery?
    (12v 7ah lead acid, or, 12v 1300mah nicd)
     
  10. mogy

    mogy

    7
    0
    Apr 10, 2011
    my circuit will determine the actual current! (didn,t seem obviouse to me...)
    anyway thanks for the help! usefull
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    Yes, your circuit determines the current. Your choice of battery should be based on current, discharge characteristics, capacity, weight, size, required run time, etc.

    The 7Ah battery has just over five times the capacity of the 1.3Ah nicad pack. You can find the approximate run time by dividing the Ah rating by the current in amps.

    So if your strings of LEDs draw 120mA (0.12A) then the 7Ah battery will last 7/0.12 = 58 hours and the nicad pack would last just under 11 hours. However it is generally considered poor form to discharge a lead acid battery below 50% on a routine basis, so 28 hours for the lead acid battery vs, 10 for the nicad pack are more reasonable figures.

    Of course these figures are based on a totally made up current draw that almost certainly does not correspond with what you have. You should repeat the calculations with your actual figures.

    It may also be a good idea to show me how you plan on connecting the LEDs so that I can double-check that you have everything correct.
     
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