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Another LED circuit

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

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  1. TheIdeaMan

    TheIdeaMan

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    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.
     

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  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    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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