Connecting LED lights directly to 12v source

Discussion in 'The Projects Forum' started by boneman818, Aug 23, 2009.

  1. boneman818

    Thread Starter New Member

    Aug 22, 2009
    1
    0
    I was wondering... I purchased some under-counter LED lights from Ikea. There are 4 individual lights that all wire back to a box with 4 connectors. Behind the 4 connector box is a power supply. The power supply lists "Input: 120v-60Hz 0.1A, Output: 12VDC 5W Max.". So if the output is 12v can't I simply connect these lights directly to a 12v source and eliminate the power supply?

    I am trying to convert these lights to be used in an RV instead of a residental home. The RV will use only 12v not 110v. I tried to connect a light directly to a car battery and got an unpleasant puff of smoke.

    Thanks
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Do you also know what is inside the box between the lights and the 12 V powersupply?
    It can be there is some current regulation inside the box for the leds.

    Greetings,
    Bertus
     
  3. rspuzio

    Active Member

    Jan 19, 2009
    77
    0
    > So if the output is 12v can't I simply connect these lights directly
    > to a 12v source and eliminate the power supply?

    LED's need a constant current source, not a constant voltage
    source. To be sure, they won't light up unless you apply enough
    voltage but, once their lit, even a tiny increase in voltage
    will make for dramatic increases in current, so your supply
    needs to limit the current.

    > I tried to connect a light directly to a car battery and got an
    > unpleasant puff of smoke.

    That's why you need to limit the current --- you found out
    the hard way :(

    The easiest way to limit the current is with a dropping resistor.

    For more information on ways of regulating current for LED's.
    please see the tattoo machine light discussion:

    http://forum.allaboutcircuits.com/showthread.php?t=26635
     
  4. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Which way do you guys think is more efficient?

    To use ~1k resistors per LED and drop directly ~9V as heat on each resistor? or
    To use a single 7805 and drop 5V to Vf using resistors per LED?

    7805 is a very lossy regulator at 12v as well as the resistors at 12v.
     
  5. Fragger

    New Member

    Aug 21, 2009
    5
    0
    Its just a thought but you could add a 120v power inverter to your rv and run your led's and any other appliances you wish, would be handy in a rv.
     
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