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How can I wire LEDs without resistors?[SOLVED]

post #1 of 26
Thread Starter 
How can I wire LEDs without resistors? Can I even do it? Like...if I had 6 5mm 2.0v leds could I just 12v/ground them on a wire going to molex without problems?
post #2 of 26
Quote:
Originally Posted by K10 View Post
if I had 6 5mm 2.0v leds could I just 12v/ground them on a wire going to molex without problems?
that would work just fine
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post #3 of 26
No No NO! they will fry, or maybe even blow up. Hook them up to 3.3 volts if you really want to direct run them. (3.3v is orange on a SATA connector)
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post #4 of 26
Thread Starter 
The answer on who to believe should be obvious but I'll wait for more replies.
post #5 of 26
Quote:
Originally Posted by K10 View Post
The answer on who to believe should be obvious but I'll wait for more replies.
Case Mod Editor, hehe .
post #6 of 26
Pulse width modulation.
 
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post #7 of 26
Quote:
Originally Posted by Idiot View Post
Pulse width modulation.
Your point?

If you're trying to say what I think you're trying to say, then you're wrong.
    
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post #8 of 26
I don't know about the small leds you're talking about but you can certainly run them in series to get lower voltage per led if they all have the same resistance. As in, if you're looking for 3 volts, just put 4 leds in series. Per Ohms law, if you have items of equal resistance, the voltage drop across each one is equal to the total voltage divided by number of items.

However, I do not know if they have the necessary resistance. Leds are sensitive to over current and I do not know if those small leds have the necessary resistors integrated to prevent overcurrent. If they do and only need 3 volts, then yes the series thing will work. I'm not sure how the 2 volts per led in a 6 string series circuit will affect the leds output. I'd say trust radodrill, I'm sure he has some knowledge of those leds.

Lastly, the reason I keep saying "those small leds" is that I have a string of 3 somewhat higher output leds used for room lighting. All three leds are in series and are being fed from a 10 volt current limited source (due to small differences in internal resistance, they range between 3-3.6 volts per led which is within spec).


Wattage per Led ~2.75 watts
Lumens:
red 75
green 100
blue ~60-70

Edit: that starburst effect isn't just on the camera, if you make the mistake of looking at these as close as the camera is here, you will see that for the second or so it takes to close your eyes and turn away.
Edited by Neutrino - 12/10/09 at 8:30pm
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post #9 of 26
@Neutrino, I don't know what you're trying to say about LEDs as Ohm's Law only applies to resistors and LEDs are a form of diode.

The fact of the matter is that wiring several LEDs in series the desired supply voltage would be the number of sum of the voltage ratings of the LEDs (for identical LEDs the number in series times the forward voltage of the LED). When wiring LEDs in series, you should try to select ones wit the same design forward current since the current through all elements in a series string is the same. The time were a resistor in series with the LEDs would be necessary is if the design voltage of the LED array is less than the available voltage supply, in that case Ohm's law would be used to determine the size of the current limiting resistor.

i.e. 6 2V@ x mA LEDs or 4 3V @ x mA in series can be powered from te 12V rail without any resistor (12V - 6 x 2V = 0).


Bear in mind, that LEDs are LEDs regardless of physical size or shape; the only rules that you have to follow when wiring an array is that for several in series they should have the same current draw and for several in parallel they should have the same voltage drop.
note: voltages add in series while currents add in parallel.
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post #10 of 26
Its possible, but I highly advise against the, the point of the resistors is to control the current passing through the LEDs

If you have a 2V constant drop LED, wire 6 in series, that will give you 12V drop, yeah sure, but what current is going through the LED's? LEDs will most likely have a suggested 20mA rating, but thats not saying they will pull 20mA.

Your best bet would be to wire as many LEDs in series as you can depending on what voltage you use (12 vs 5 vs 3.3) then add one resistors to control the current.
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