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if i wired up a series of leds... such at the one in the diagram... each postivie goes to each negative.. and the one in blue goes out.. would that stop the circuit to all of them or would just one stop working?

 
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It'd kill the whole circuit. Also, if you want a uniform brightness, wire them in parallel, otherwise the voltage drops after each LED and it sorta fades.

 
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so would this be the right way? also.. if i had like.. 20 leds wired up this way... how would i kno what size resistor to use if i juss added one at the begining part of the wire?

 
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how would you know which resistor to use, i'm interested.

 
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depends on the voltage of the diodes for what resistor.

(source voltage - diode voltage) / resistor value = under diode's max current rating. this will be a value in mA.

example: 12V source, 1.7V diode with 20mA rating. 515 ohms would be the smallest resistor value you should use in this case.

 
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wouldnt you put the reisitor between the battery and the LED's? Im not really sure about all the rules but thats the way I did it and they work great.......

 
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it doesn't matter where it is as long as it's in the circuit. one way isn't better than another.

 
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no it HAS to be on the negative side.. cus the electricity starts from the negatiive and goes to the positive.. and before all that power reaches the bulb.. it needs to cut it down.. so its best to put it on the negative side... ALSO.. how would i kno which resistor to put on it of u have multiple LEDs?

 
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when you say electricity, i assume you mean current. and while some people read that and go HEY, current flows + to -, you are technically correct, it flows - to +. but why have we stuck with ben franklin's incorrect model for over 200 years?

because it doesn't matter how you assemble it, it's the same result kirchoff tells us so.

for the diagram you gave me to work with, you would HAVE to use diodes with the same voltage value. BUT when doing the math in the equation i gave you, you would only use that value ONCE (1.7V, not 1.7V times the 4 diodes).

to figure in the multiple diodes, you would add up their max current values (20mA times 4) and plug it into the equation i gave you.

NOTE: don't worry if you can't get a resistor right at the max value. don't even worry about getting too close to it. it only takes a few mA for a diode to get at about 90% of it's max brightness. i usually don't bother doing this math and just throw a 1k ohm resistor in because i know i'm not gonna blow anything up and the diode will be really bright.

 
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there is no reason why the first diode would be dimmer than the last diode in that diagram. they all get the same current, they all light the same (assuming same type of diode)

if you put a resistor before ground in that first picture you drew (LED's in series) then you would be OK. or at the beginning, but whatever. for THIS math, you WOULD add up the diode voltage values (1.7V in my example times 4 = 6.8V) and then for the max current value, use the max of ONE diode (20mA in the example).

both series and parallel wiring will give you the same result

 
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ok i want 24 LEDs wired up and i used sum led calculator.. and the resistor thing said... -1800 ohms... that seems rong lol..
can u help me out? 12 volt source.. led voltage: 2v... led current: 20mA
and i want 24 wired up like the SECOND picture..
also if i wired it up like the first picture.. and 1 led went out.. would it cut the whole circuit?

 
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Too much writing, but the resistor goes BEFORE the leds. Battery power, to resistor, then to leds, then to ground. Otherwise you will have fried LEDs if they're hooked straight to the battery.

 
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When I did my blue dash, I wired the needle leds in parallel (much more complicated), and the rest in series. Didn't notice any decrease in brightness. All of them are coming from the same power wire.

You can put one big resistor in front of all the leds, or put a single small resistor in front of each led in series. Refer to my diy for more details.

 
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use ^^^ that method and i assure you you can wire 1000 LED's up in theory.

sounds good. but not true. current flow is determined by resistance. diodes have either none or infinite, depending on wiring. thus the resistor is the only element determining current flow.

 
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Explain? If I hook a led straight to the battery, it will blow out. I know this because it's happened before. Or are you saying the location of the resistor doesn't matter, as long as you have it somewhere in the circuit.

 
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you need some resistor to determine current flow because diodes won't by themselves. location in the circuit doesn't matter.

 
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ok still didnt get my answer... i tried all tha formulas.. and im not getin ne thin rite... if i had 24 leds wired in a parallel like the one in the pic.. and i juss wanted one resistor instead of having a bunch of emm on each led... what size resistor would i use? 2.2 current.. 12 volt source.. 20 mA??

 
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You need to search. The info is all over the place. But I'm nice, so here's something to get you started. There's alot more info on this site as well.

http://www.k-series.com/tech_detail...._CON_LITE_SWAP

http://ourworld.compuserve.com/homep...Bowden/led.htm

 
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ok i think why you might not be getting it to work is because for the formula the current value should be in AMPS, not milliamps.

(12V-2V)/resistor = .48A

so the resistor should be like a 20.8 ohm. so buy a 24 ohm resistor and call it a day. make sure the resistor can take .5 mA or 12W power dissipation.

again, this is for the parallel method, using one resistor either after the source or right before ground.

 
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I like the picture!

 
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Check out www.lsdiodes.com there is a lot of info and a calculator on there, the best way is to get several values of resistors and experiment.

LEDs WILL EXPLODE !! NO JOKING.

 
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that first image u posted. of the 4 in a row like that. assuming your leds are 3 or 3.5 volt. like many are. would work fine. they would jsu tnot be there brightest

check ebay. guys on there sell lots of led's with resistors for 12v use.

and your gonna get the best response out of one resistor per led.
trust me. i've installed hundreds of the lil basterds

 
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Wow, this was brought back from the dead. I hope you got it working.

 
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oh wow didnt even realize it
why do you people insist on searching back threw threads to revive them lol


oh an explosive led's sends some plastic atroudn and small spark.. wont kill you