so if i pick a resistor like you said 66 ohm but 68 would be fine . i would want to go with a higher value i assume? great posting btw!

 

You want to go with the a value same as or greater than the result. If you go with a lower value, you will likely shorten the expected life of the LED.

 

what gauge wire should i be using i have 22?

 

AWG-22 stranded wire is used for circuits carrying 5A in aircraft, so yes - you can use AWG-22 wire.

 

on the atx power supply. what color wires will i use for the 12v and for the 5v? i have the red,black and yellow plus one white orange and blue. is there a load sense?

 

on the atx power supply. what color wires will i use for the 12v and for the 5v? i have the red,black and yellow plus one white orange and blue. is there a load sense?

Yellow wires are +12v.
Red wires are +5v.
Black is ground.
Orange is +3.3v.
Blue is -12v.
There is no "white" wire in the ATX specification. It's probably grey.
See the ATX specification, here:
http://en.wikipedia.org/wiki/ATX

 

come to find out its a liteon pa-4151-9b 190309. does that change anything?

 

That is an LPX supply; very old, 150W, sort of like a small AT power supply, and it is not ATX compatable; so the conversion I linked you to won't work.

One of my favorite suppliers has 150W ATX supplies on sale for ~$6 plus shipping:
http://www.mpja.com/prodinfo.asp?number=18034+PS

They also have a number of regulated "desktop" supplies in the $9 price range:
http://www.mpja.com/Category/Power_...ies/Desktop_Power_Supplies-Power_Supplies.asp
The 16v or 20v supply for $8.95 should be adequate, and you wouldn't have to buy extra items to convert an ATX-form factor computer power supply; just find a suitable jack to plug the connector into.

 

so ive managed to get my psu supply to work but its only giving out 11.35 volts. how is that going to change the number of leds in the series? value of the resistors?

 

so ive managed to get my psu supply to work but its only giving out 11.35 volts. how is that going to change the number of leds in the series? value of the resistors?

Would be nice to see a circuit at this point.

I can only guess it will not matter for the number of LED's but it will change the resistor values.

 

i changed the resistor values to 46ohms across all strings. on the 5 string and the 4 string.

 

so ive managed to get my psu supply to work but its only giving out 11.35 volts. how is that going to change the number of leds in the series? value of the resistors?

You are probably not getting good regulation on 12v because there is little or no load on 5v. ATX form factor supplies require a couple of amperes load before they'll regulate the other voltages halfway decently.

 

ive change the value of the resistors to 47 ohms for both the 5 and the 4 string leds. do you think that will burn them out?

 

Did you change them after calculating the values?

Did you try placing more of a load on the 5v output to see if 12v will come up to where it should be?

 

i calculate the 5 red string and got 46 ohms. i was following the work you posted before. i however didnt on the mixed 2 red and 2 blue. i wasnt sure how to do the math on that one. can you help? i did put a one watt led on and it went to 11.48 then i tried a pc fan and went to 11.67v do you have any ideas on what to do?

 

Try using a couple of 10 Ohm power resistors (10W or more suggested) across the 5v supply, and then measure your output voltages.

 

i put two 10 ohm 10 watt resistors on the 5v line and the voltage increased to 11.90v. is that going to be enough with the resistor values you gave me? the blues and uv are barley lit up.
How do i figure out the ohms resistence with two different ma and Vf values together?

 

I believe I went through all of the math before, but let's go through it one more time:
Rlimit >= (Vsupply - (total of LED Vf's at desired current)) / Desired Current
So, if you have an 11.9v supply and several LEDs in series and want 20mA current, you would calculate:
Rlimit >= (11.9v - (Vf_LED1 + Vf_LED2 {... + Vf_LEDn})) / 0.02