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Modding Led + Resistor + Molex = Now What?

Discussion in 'Modding' started by jbehmoaras, 9 Jun 2004.

  1. jbehmoaras

    jbehmoaras What's a Dremel?

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    I have these UV LEDs with these specifications:
    SOURCE MATERIAL:InGaN
    EMITTING COLOUR:pURPLE (UV)
    LENS TYPE:WATER CLEAR
    PEAK WAVELENGTH (TYPICAL):400
    REVERSE VOLTAGE:5.0 V
    DC FORWARD VOLTAGE:3.7V TYPICAL
    DC FORWARD CURRENT:20mA
    VIEWING ANGLE:15 degree
    LEAD SOLDERING TEMP:260oC for 5 seconds

    They also came with some resistors. Can some explain to me how many LEDs i can hook up to one molex coming out of my 600W psu. This will be the first time i will be hooking up some LEDs so if you could include some detailed intructions for someone who doesnt know much about electricity that would be great
     
  2. Blue Raven

    Blue Raven What's a Dremel?

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    It would help if we knew what type of resistors they are. There should be colored bands on the resistor, what are they and in what order.

    To know how to hook leds up, it is useful to know the basics. Leds need a specific current to operate. They also have a specific voltage drop across them. From reading the specs, your leds need 20 mA and have a voltage drop of 3.7 volts. From this information you can calculate the value of the resistor needed. Let’s say that you are running it from 5 volts. we subtract 3.7 (your led voltage) from the 5 volts. This gives us 1.3 volts. We now need to find a resistor that will allow through 20 mA at 1.3 volts, for this we need ohms law. Ohms law is V=IR, V stand for voltage across the resistor, I stands for current flowing through the resistor and R stands for the resistance. We know V an I so we plug them in to get 1.3=0.02R. Since we want to find R, we rearrange the equation to get 1.3/0.02 = R or R = 62 ohms. Because there is no 62 ohm resistor, we use the next closes values, 51 or 68. You solder the resistor between the positive lead of the led and 5 volts, or between the negative lead and ground. Make sure to get the polarity right or the led wont work.

    If you want a string of leds, you put them in series (one after the other) with and add their voltages together to get the forward voltage of the string. You use the same amperage in the calculation. if you have leds in a string, the voltage cannot exceed the voltage of the power.
     
  3. jbehmoaras

    jbehmoaras What's a Dremel?

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    Thanks for that desciption. The resistors have an overall blue color with stripes. The stripes are in this order: yellow brown black black brown. Since its on a blue background, the black could be a really dark navy, and the brown can be a dark red color. Since i dont know how to read it i dont know if that makes a difference or not
     
  4. woodshop

    woodshop UnSeenly

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  5. Leadpipe

    Leadpipe What's a Dremel?

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    I bought LED's from the same guy. Those are for working with 5v, I believe the red wire on your molex. There's lots of guides on how to use them around.
     
  6. Blue Raven

    Blue Raven What's a Dremel?

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    As woodshop said, the resistors are 100 ohms. If you put them on the 5-volt line, you will not get full brightness because you have only 13 mA flowing through the led. If you want to get full brightness, I'd suggest calculating the correct resistor size and buying it from an electronics store (look in the phone book for local stores). To simplify the calculations, try here. There are three led calculators here for a single led, led's in series, and in parallel. With the proper resistor, your led's will be at full brightness.
     

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