1. ## Re: LED Wiring Tutorial

Originally Posted by JimChud
I've already read that tutorial, i just wondered why people had done it differently i personally would have thought it would have gone at the front before the diodes.
It makes no difference whatsoever.

* 2 series of 4 LEDs in parallel with a 120 ohm resistor at 1/4w on each series.
That's what I'd do, assuming I understand you correctly. Two strings, each comprising four LED's and one resistor in series. Fed from 12V.

120R will give you 16.6mA which ought to be fine. 100R will give 20mA.

2. ## Re: LED Wiring Tutorial

great tutorial, so what excactly does a resistor do i was taught in scince but i didnt really listen/ understand show if someone here could tell me what they do would be great.

3. ## Re: LED Wiring Tutorial

it coverts a certain amount of energy in to heat and thus reduces the energy in the circuit.

4. ## Re: LED Wiring Tutorial

Originally Posted by JimChud
it coverts a certain amount of energy in to heat and thus reduces the energy in the circuit.
Well, yes, but that's not really why we use them.

It controls the current in a circuit. Current through a resistor is proportional to the voltage across it. Double the voltage, double the current.

In an LED circuit, you need to control the current through the LED. The resistor does this.

An LED has a certain operating voltage. In this case it's 2.5V. Put a higher voltage across it and it will attempt to drag that voltage back down to 2.5V by drawing so much current that the power supply drops. Obviously, with a computer PSU, it will take a LOT of current to achieve this, and the LED will simply burn out. With the resistor in place, the resistor will limit the current for you.

5. ## Re: LED Wiring Tutorial

Yes, I tried a 3 watt LED directly through my 550W PSU, I think on a 12-volt rail, and it got very hot, so I let it drop within a second. It was scorched and burned, and would not work again when I tried it.

6. ## Re: LED Wiring Tutorial

Originally Posted by nevermind1534
Yes, I tried a 3 watt LED directly through my 550W PSU, I think on a 12-volt rail, and it got very hot, so I let it drop within a second. It was scorched and burned, and would not work again when I tried it.
that is precisely why we use resistors.
i wouldnt be shocked if you popped it.

i would recommend looking at the above LED Guide to see what you need

7. ## Re: LED Wiring Tutorial

I've got some LEDs already matched with resistors, so I think I will run them all in parallel off of a 5V rail. It is going to be for a school project, and I'm only powering a fan and the LEDs.

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