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12 volt led 12v battery

Discussion in 'Power Electronics' started by conntaxman, Dec 31, 2011.

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  1. conntaxman


    Jun 17, 2011
    I have some 10 watt leds 12vdc. I want to run these on my system that is/will be 12volt.I know that the charge contorller will bring it up to about 14 volts sometimes, and start to re-charge at about 12vdc. My Question is can I just put in a resistor to run the led? A LM317 needs 3 volts more,so that wont work,[i don't think]
    I want to run a few of them.
    The larger leds are mostly 12 volts and up.
  2. GonzoEngineer


    Dec 2, 2011
    What kind of LED.....can you give us a part number? We can't help without more info.
  3. conntaxman


    Jun 17, 2011
    12 volt 12v battery

    here are the spec. it didn't show the amp. I'll be using about the same as other 10 watt leds.Right now i have it on a 1watt restor, i "THINK" its 1 ohm. and it works
    Color: white
    Luminous flux: 1400-1600LM
    Forward voltage: 12V
    Color temperature: 6000K-6500K
    Power: 20W
    Lighting angle: about 140°
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    You really should consider a constant current driver.

    The problem with running a LED from a voltage close to its rating with a series resistor is that the voltage across the resistor is small. If the input voltage changes, the voltage across the resistor can vary dramatically, causing the LED current to fluctuate widely.

    A 20W device is unlikely to have any inbuilt series resistors.

    Running LEDs from a voltage source only slightly higher than the LED voltage can be tricky. How many are you running? It may be better to place a pair in series and then use a boost SMPS with current limiting.
  5. conntaxman


    Jun 17, 2011
    12v 12battery

    I think i found what will work
    The LM2940CT-12 is a 12V low dropout voltage regulator integrated circuit (pictured above). It can output up to 1 Amp at a fixed 12 Volts DC with a dropout of just 0.5 Volts. It can accept input voltages from 5.45V to 26V DC. It can therefore be used to provide a fixed 12 Volt DC supply to a string of up to ten 12V 1 Watt LED spotlights guaranteeing their longevity.

    NEW The LM2940CT-12 is now available for sale in the REUK Shop.

    When the input voltage is below 12.5 Volts - as will happen if you let your battery drain below 40% charge, the output voltage will be approximately equal to the input voltage minus a voltage dropout of 0.1 to 0.5 Volts. With a current draw of 0.4 Amps, the input-output voltage differential is 0.25V, and it is 0.5V at 1 Amp, and just 0.1V at 0.1 Amps.
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