Leds in a Computer Case

Discussion in 'General Electronics Chat' started by Tristan, Nov 27, 2005.

  1. Tristan

    Thread Starter New Member

    Nov 27, 2005
    2
    0
    Hi all: I am wanting to install some led thingys in my computer case. However, I want these to be "always on", and am going to use a separate pc power supply for them.

    Anywhere I have looked on the internet, it is said that you need to ensure that you use a resistor with the led's. However, there are many manufacturers who make various led light configurations for use in a computer caase that do not appear to have any resistor(s).

    I have purchased several led's for my computer, which come pre-wired with molex connectors. These simply plug into the normal pc power supply. Usually they have only two of four pins in them, and these are the ones that mate to the 12v supply from the transformer. There is no resistor in these (I have taken one apart to see). So, my question is, why do these led's not need a resistor?

    Thanks.
     
  2. Overclocked2300

    Senior Member

    Apr 24, 2005
    124
    0
    They probably do have a internal resistor, or they are of the blinking type and blink so fast you cant see them (so they always look like they are on)

    I use 270 Ohms for my LEDs on 12V.
     
  3. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    Either they have an internal resistor, or are made to with stand a computer power supply. Diff LED's have different current capacities.
     
  4. Tristan

    Thread Starter New Member

    Nov 27, 2005
    2
    0
    One of the products I have is this one: http://www.sunbeamtech.com/PRODUCT11.html

    Is there a way to tell if the led has the internal resistor?
    Where would you buy such led's?

    Thanks.
     
  5. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    You don't need a 2ndary power supply. You really dont. Most leds have a 1.4-2v drop across them and u can get them to light with 10mA quite bright = 10-20 mW of power. Not even a tenth of a watt and a PC power supply can push out typically 300-450 watts depending on what u have in it. You could light 50-100 LEDs without even making the power supply notice it.

    I have a PC with 4 additional fans installed, all are between 10-30 Watt fans because the PC is so overclocked, so thats an extra 60 watts about I am pulling off ofthe supply without an issue. Now, if I had one of those nifty AGP ATI cards which tells u to have a large power supply, I would have an issue with that PC.

    Now, if you want the LEDs on even when the PC is off, don't waste money on a PC power supply. Extra heat, space and money, bleh. You can light all ur LEDs using a simple 5v-12v power pack u can buy for under $10, or you can steal from something you own with an etxra power pack. Keeps the extra heat out of the PC case and doesn't waste any space or impede air flow.

    They typically put out 500mA upward to 1000mA, you can get 50+ LEDs out of that very easily. Shoot, with the 12v 1000mA, you can do LEDs in series, like 4-5 of them, 1 res. Each series line would be, say, 10mA, so from the 12v 1000mA you could get up to 400-500 LEDs, lol.

    Those pinned LEDs do have a res in them to limit current flow but not a typical res you will find. Just like a xtr has an internal res, some LEDs are manufactured with an internal resistance within them, especially when they are used in a very controlled environment. i.e., if you always plug them into the molex, they know exactly what voltage will be there, either 5 or 12 so they are manufactured for those voltages.
     
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