I'm modding for the first time and I wanna put in some extra LEDs, I tried wiring them off the stock power LED wire and I noticed that the lights started to vary in brightness.

I dont wanna risk stressing the m/b if too many LEDs can do that, and the varying brightness looks real gay. Is there a way to wire them from molex connectors or straight from the psu? If so wat resistors do I use and how do i set it up?

Any suggestions welcome.........

It shouldn't stress the mobo out, but that is not the most efficient way anyhow. Most of the time, the more LED's you put the dimmer they all get.

I always add extra LED's straight to my PSU through a molex or something that connects to a molex. Most people use the 5v(red) rail. I use the 12v(yellow) rail. As for resistors, what are the specs on LED's...just need to know the voltage and how many mA it pulls....then we can answer the resistor question, and continue further.

12V DC is awesome. You could run the world off 12VDC.

To figure out what resistors to use you need the following information:

• Supply voltage (either +5 or +12 from power supply)
• Diode rated voltage
• Diode current draw

Once you have that information visit Linear's LED Calculator to determine the appropriate resistor to use.

So you got four lines on a molex which one do i stick the leds on? Can I put them all off one molex or does it have to be one per each molex?

I think i got 3.5v 20mA 1000mcd LEDs...

the typs of resistors should be in ohms yeah? But the local electrical store i go to got them in watts, what does that mean?

Sorri dudes, I missed a bit before, so i connect them to the yellow rail, whats +ve and wats -ve? How do i connect them to the actual connector? Coz I got connectors to waste... THankx for helping me out

The yellow wire and black wire next to it are 12V positive & ground, respectively. The red wire and black wire next to it are 5V positive and ground, respectively.

If you want to feed the LEDs 5V, use the red & black wire. If you want to give 'em 12V, use the yellow & black. Also, if you want your fans to work at their fastest, always make sure they're getting 12V (yellow & black).

You may need a resistor for your LED, to limit the incoming power to prevent blowing it. Typical AVERAGE 5mm LED power ratings are:

Red, Yellow, Green: 2V
White, Blue, UV: 4V

LEDs generally draw .02 Amps of current.

Use Ohm's Law to calculate resistance.

Resistance = Voltage (supplied - required) / Current

Therefore, for a single blue LED on the 12V rail would require:

R = (12V - 4V) / .02
R = 8 / .02
R = 400 Ohms

Then, you make sure that resistor is connected to the POSITIVE end of your LED, between the incoming 12V power line and the LED:

12V power->400 ohm resistor->blue LED positive tail
Ground->blue LED negative tail

Hope this helps! I'm getting good at this, I was forced to ask a lot of questions and do a bunch of research after blowing one of my LEDs.

You mentioned Watt? LOL

Yes, resistors are also rated by watts.... 1/4 Watt should do just fine.

as for the 400ohm resistor, they may be difficult to find. I always round up to the nearest common resistor. 470ohm 1/4 Watt resistor is very common(as in you can find them at almost any RS) and should work fine without much loss in brightness. But if you can find some that are closer to 400ohm but not less, get those instead....of course. If your LED calls for a different resistor(by using the formula Coel posted), just always round up to the closest resistor if you can't find the exact one you need..

You have got to hate the good ol' nuthin emittin friodes. Can't stand blowing money like that.........

BTW I have 22 bL0oo LED's in my Starship Rig.......Bl0oo may be overdone but it is still the most attractive LED. IMHO

Quote: Originally posted by OMFG_dude_WTF as for the 400ohm resistor, they may be difficult to find. I always round up to the nearest common resistor. BTW I have 22 bL0oo LED's in my Starship Rig.......Bl0oo may be overdone but it is still the most attractive LED. IMHO

The 400 ohm thing was just an example. I had no idea they're rare. I used a 200 ohm resistor with a 4-red-LED array on a 12V line, 200 ohms is the largest resistor I've needed. Blue is definitely popular now, it IS a very nice color and very bright, but I'm using red primarily for my current project. Green just wouldn't have matched the planned 'theme', white wouldn't work with the color my case will be, blue is only being used in a few places...and purple, I couldn't find yet.

god damn did they not teach you OHM"S LAW in 8th grade!?!?
it boggles the mind that so many people ask. you all took science and hopefuly got past algebra. unless you dropped out. or are too young. when i mooded my key board light there was no external current limiting resistor (i assume its built in to the chip) for the leds so i had to be very careful to to blow out the keyboard chip. just to be safe a SMD resistor and the x acto knife to the rescue. and its not that important this keyboard was from boeing surplus so is this nice sony 17 inch monitor. and i think dad took this optical mouse from work.
by the way when i desolder stuff i use a desoldering wick. they say the blubs and syrenges are posible static accidents waiting to happen. and flicking it off never works.

before you all flame about how modding is spelled mooding i cant edit my posts so dont complain about my grammar or spelling.
i looked through the parts bin and here is a yellow black brown gold resistor. you know what that means then there is the yellow military stripe. its a half watt. i think im not supposed to have this....

Quote: Originally posted by carbongraphite before you all flame about how modding is spelled mooding i cant edit my posts so dont complain about my grammar or spelling. i looked through the parts bin and here is a yellow black brown gold resistor. you know what that means then there is the yellow military stripe. its a half watt. i think im not supposed to have this....

carbon, people who complain about typos are lameasses. Don't worry about it. However, I think you've had enough alcohol for one night--I don't know what in the hell you're talking about in your last paragraph!

Carbon....me trying to remember Gr. 8 would be somewhat akin to you trying to recall your first poopy on the potty.

I have 10 years of post secondary education in the sciences, and I look up Ohm's law every single freakin' time!

Go easy on us old farts!

ok if you didnt get it yet
first band yellow = 4
second black = 0
third brown =0
so first and second is 40 then times third is 10
40 x 10 =400 ohms
fourth gold is 5% tolerence and the fifth is the military failure rate. yellow is 0.001% / 1000 hours
confused yet? dont worry they make cheater cards that have wheels you can move for each color.

...means jack sh*t to me. LOL I just keep my resistors clearly marked so I don't need mathematics 'make-work' projects.