LED diy Electrical Guide help?

SuperSaltwater

New member
ok so i watched a video on youtube that shows how to use a pc power supply for multiple 10w led lights. saves $$ on drivers...

guy said to use a 2 watt 2 ohm resistor on each + of each LED. so i wired 4 x 10w leds and added the 2 watt 2 ohm resistor to each, i wired the - and plugged it all into the yellow and black wires (12v) on the pc power supply. worked great and turned on. my power supply has 25amps total and was told that i can add up to 25 x 10w leds (1 amp each?). so this is a great way to save $$$ on drivers.

so my question is...if i cant find a 2 watt 2 ohm resistor, what other resistor would work? what do resistors do? what are the amps? if my power supply is 300 watts does that mean i can use 30 x 10w leds? or does the amps tell you how many 10w leds you can use? is there a guide that explains all of this stuff? i want to know how to figure out when to use resistors and what watt and ohm. i want to understand amps, watts, volts etc...

im new to led DIY and built my first 40watt already (for 5 gallon growing chaeto 3x65k 10wled 1x27k 10wled). i want to build a wide variety of lights and need better knowledge...:(
 

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Ohms law..
So lets assume..
Vsupply=12V (voltage of constant voltage supply..like a PC power supply)
Vf = 10 (forward voltage rating of LED)
V = Vsupply - Vf = 2
R=resistance
I=current we are feeding the LED with

Lets pick this forumla from "ohms law" (google ohms circle or wheel)
I=V/R
I=2/2 so I = 1 Amps


Now to determine the proper wattage of the resistor then
Its V x I = W (watts)
So 2 x 1 = 2 watts
BUT a 2 watt resistor dissipating 2 W is WAY TOO HOT.. You should always double the wattage as a "safety factor"
So the wattage should be 4W (5W is common and should be used)

Change the values around and have fun..
 
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