LED idea brewing! need affirmation on design/wiring?

So this will be my first LED project and after reading just about all there is to read i think i have it down, but b4 i go out and buy everything i want to consult the PRO's and see if it is right and turn this into a instructable. So if you could take a gander at the attached professional scribbled design and give me some feedback id appreciate it. and to clarify im not sure if im going to run this off of 120v or 12v. Thank you!!

Picture of LED idea brewing! need affirmation on design/wiring?
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iceng5 years ago
Series does not matter on the order ! ;-)
ARGMISTER (author)  iceng5 years ago
ok thanks i understand now.. but not fully, i guess there's always a why!!! but that's for later. Thanks for your help.
NEVER run LEDs in parallel !!!
ARGMISTER (author)  steveastrouk5 years ago
if your power supply is rated higher then your leds right? cause then they would blow up if you put 12v to 3v leds...no matter how many cause each one is getting 12 volts right?
frollard5 years ago
do not run leds in parallel with only 1 resistor. Each parallel led (or string of leds) needs a method to control the current. Voltage doesn't hurt diodes (within reason), current does.

Otherwise your design isn't terrible. Another problem I have with it is you're running SINGLE leds on 12 volts (as you said, they're parallel)...that means you use 3.3 volts and WASTE 8.7 volts...throwing away almost 70% of your energy.

Save you the math, use a wizard like http://led.linear1.org/led.wiz

3 leds
12 volts
20 ma
3.3v each

...yields 120 ohm resistor and 3 leds in series...

Make a bunch of those strands, 3 leds and a resistor...
then put THOSE in parallel on 12 volts.

(run the wizard again with 30 leds instead of 3 and you'll see what I mean)
ARGMISTER (author)  frollard5 years ago
Would the attached picture be sufficient? or should i do 3 leds instead of 4 in a row?

I was on ledz.com and the site you referenced and was confused on the referenced site it shows the resistors AFTER the leds .......is that correct?

and im not sure what voltage my leds are yet, i have to do a test on them to find out but calculating the power supply which is 3 aaa batteries and the lines on the resistors i think they are around 3.3. I need to get a multimeter to be sure, they light off of a 3v button battery.

Thank you for your help, i wasnt sure if 12v is enough to power 64 leds thats why i mentioned 120v, ive installed an array of sockets and fans when remodeling both my parents house and have been shocked twice by 120v....it doesnt feel very good...def not something to mess with.
iceng ARGMISTER5 years ago
From where bwrussell suggested you visit.
21 groups hare to show.
Hope you understand.
ARGMISTER (author)  iceng5 years ago
I think to simplify things i might just go with 3 leds in parallel instead of 4. im pretty sure it should still have enough light output.

and i really want to learn how to wire up leds and currents and resistors so id rather do hands on and my own math so i understand it rather then just copying pictures and filling in the boxes
*and please please please don't mess with 120v until you thoroughly understand how voltage and current work. Not only will you blow up your leds in the above example on 120v, you can easily hurt yourself.
bwrussell5 years ago
THIS has an easy to use calculator for building series-parallel LED arrays with dc power supplies.
iceng5 years ago
It's a very old rule that,

LEDs of a color do not light parallel to one another.
iceng iceng5 years ago
64 led of 20 ma each would draw 1.28 amperes and need a 6.8 ohm resistor of 12 watts...

Better a series of 3 leds and resistor group in parallel with 20 more groups
for a total of 63 leds is an engineering proper solution.