Parallel circuit resistor calulation help

[SparkleDJackson]

Hey guys. I have ordered the 300 smd leds i need for my build. Now im not sure how exactly to calulate the value of resistors i require. I will be constructing a parallel array with one led and resistor per level. Im not sure how many smds i will use so if anyone knows the formula that i can use to calculate the values i need that would be awesome even if you could give me an example i will give the current values i know

Source voltage 12V

Led forward Voltage 3V

Led forward current 20mA

Example number of leds 10(1per level)

That would be INCREDIBLE if you could give me that example

Cheers

 

[Grizzly]

I think what you want is a 450 ohm resistor for each level, that will take 9V off of the 12 V supply leaving 3V for the LED (which should have a 150 ohm resistance).

Assuming you've got at least 6A on the 12V rail it should work.

For future info for each component voltage = current x resistance

In series current is consistent and voltage is split between components.

In parallel current is split across levels and voltage is the same on each level.

 

[SparkleDJackson]

So i calculate it as the voltage drop i require by the amperge

 

[Grizzly]

So i calculate it as the voltage drop i require by the amperge

For each level yes.

Happens to be remarkably easy values to work with.

To have 3V across the LED with a 12V supply you will need 12-3V across the resistor, so 9V.

From there you can see a ratio of 1:3 for the voltages.

So to get the resistance value you need to calculate the resistance of the LED, 3 / (20x10[sup]-3[/sup]) = 150.

This will be the 1 in the ratio.

Then times that by 3 to get the resistor value required, 150 x 3 = 450.

This is the 3 in the ratio.

 

[BKCXb]

your gonna need 2 watt resistors though.....