where can i buy LED's?

[.Froot.]

Why not use the 5v bus? Then the resistor will be smaller?

No difference between using a big or small resistor (price based). 12V and 5V will only require that current stays the same.

 

[DDV TECH]

No difference between using a big or small resistor (price based). 12V and 5V will only require that current stays the same.

Just for interest sake, would a smaller resistor not give off less heat? I’m just thinking if you going for 20+ LED’s .

 

[.Froot.]

Just for interest sake, would a smaller resistor not give off less heat? I’m just thinking if you going for 20+ LED’s .

Nope. No difference. Remember that if you use 20 LEDs you might just need two 12V rails. Those LEDs do get a little uncomfortable to touch but does not give off heat beyond 0.5cm radius. The resistors don't get hot at all in my experience. Unless of course you try and churn too much current through them. Could you maybe tell me what the current output is of the 12V rails there?

 

[scotty777]

um, it's a lil confusing, but it says 3.3v is running @30 amps, 12v is running @18A and 5v is running @ 28 amps, sooo,

 

[.Froot.]

Yeah, that sounds about correct. Usually, as the voltage increases, the current decreases. Resistance stays more or less constant.
If you pop in 20 LEDs in the 12V rail, you will have 18A spread across 20 lines (talking about across the LEDs here). ->12V, 900mA. A 4.7kilo-ohm resister for each LED will be needed then (if it is too dim, decrease the resistor by around 1/2). 4.7k is a standard size btw.

 

[Peder]

i have actually never seen a LED go pop except of course if you put 12V through it and thats unlilkely if you keep the LED's in Parallel as harddrives are also power sensitive

 

[.Froot.]

i have actually never seen a LED go pop except of course if you put 12V through it and thats unlilkely if you keep the LED's in Parallel as harddrives are also power sensitive

The voltage is not really the issue (in terms of limits). But current is. Increasing the current increases the brightness until it can't take it anymore, then lights-out. You just blew the diode.

 

[Peder]

oh ok i think i understand thats why i was always told to put a certain resistor on my LED's?

Or am i wrong?

 

[.Froot.]

Well you have to divide the voltage by the current you need -> ie you have 12V (voltage stays same in parallel) and you need ie 25mA -> 12/0.025= 480ohm so you can use anything from a 450-600ohm resistor. (Never mind the 4.7k, I added an extra 0 somewhere previously).

 

[nihilist]

Last time I looked, www.electronics123.co.za seemed to stock 'em.

 

[sn3rd]

Putting them in parallel will put the same voltage through each of them, requiring a resistor in series with each LED. The current rating is more of an upper limit rather than a "I'm going to pump 18A through this line, careful". So if you put a 1k resistor in series with an LED on a 5V rail, you have i ~ V/R = 5/1000 = 5mA on that line (and thus through the LED). Obviously a smaller resistor will result in a larger current, so you need to make sure that the resistor limits your current enough to fall within the limits of the LED. In general, 18A is plenty to share around for all the resistors you could possibly want (within reason), but remember that other peripherals in your computer use that current too!

Oh, and super-bright LEDs (suprisingly, cheapest at RS Components, Kyalami) are the shiznit.

But froot's advice should do the trick

 

[.Froot.]

Electronics123 do have it, heck they've got most of the stuff Communica has, but they are a lot more expensive. I know that from experience. I usually do the 14km extra to Communica if I can spare the time.