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Another LED circuit

Discussion in 'LEDs and Optoelectronics' started by TheIdeaMan, Jan 11, 2011.

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  1. TheIdeaMan


    Jan 11, 2011
    I am trying to design a LED light with a power supply of 12 volts 2 amps. I am going to use 6 LEDs total. I bought some 3 watt LEDs off of eBay and are rated at 3.3 volts 700 mA. I used one of the LED calculators to figure out which resistors I needed (2.7Ohm) but I also saw some that said to use a 3.3Ohm. I have them wired as shown but they are not that bright. Just out of curiosity I tested one of the with 2 AA in series to see how bright they should be and they are no where close. What have I done wrong?

    I have also thought about rewiring them with 3 different circuits that have 2 LEDs per circuit.

    Attached Files:

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    These are high power LEDs. Whilst you can do what you're suggesting, it is by no means the best way.

    The sticky thread "Got a question about driving LEDs?" would be an ideal read as it has answers to all of your questions.

    By the way, I calculate 1.7 ohms (use 1.8) but beware that if you're using a car battery and the voltage is higher than 12V then you stand a very good chance of damaging the LEDs.

    I'd also measure the voltage across one of those LEDs just to see if 3.3V is what you see in practice. If it's a bit higher, that would also contribute to them being less bright.

    Measuring the voltage across the resistor is also a good thing because it will allow you to calculate the actual current.
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