Connecting 5 12V LEDs in a parallel circuit

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I recently bought 5 12V ultra bright LEDs (all identical), and want to hook them up to a battery pack of 8 AA batteries. So I figured I could just make five parallel circuits with one LED in each, and hook them all up to the 12V DC. Since I'm quite new to hobby-electronics, I'd like to hear your input.

1) First of all, I've read in a related question that it's a good idea to always have a resistor in such circuits, even if the voltage matches the LED exactly. How many ohm should this resistor be?

2) It's ok to put the resistor "before/after" the the 5x parallel circuit, right? Or should I have 1/5 the resistance in five resistors, one in each parallel circuit?

3) Since the circuit now has a resistor, and it works by generating heat by consuming power, won't the battery be drained quicker with such a resistor in the circuit?

4) Finally, are all "regular" LEDs 20mA?

Best Answer

If these are 12V LEDs then they most likely have some sort of regulation built in, so you don't have to worry about putting in a resistor. If you have the documentation for them, I would put it in your post.

2) If you wanted to put resistors within each parallel circuit, it would also need to have the same resistance as the one you would put at the beginning or end node, not 1/5. The advantage of doing this is that you could have smaller resistors rated for a lower power than one big resistor rated for a high power.

3) Short answer, no, the resistor is generating heat that would have been made at the LED if the resistor wasn't there.

4) Those don't sound like regular LEDs, but if you mean LEDs like the through hole 3mm or 5mm most of them are indeed designed for 20mA current draw at a characteristic forward voltage.

LEDs are non-linear semiconductor devices, their current draw is non-linear with the voltage across it. Look at this graph to see what I mean. http://en.wikipedia.org/wiki/File:Diode-IV-Curve.svg