Hi, i was wondering how many of these LED's i'd have to wire in a series to support a 12v imput ( from a car of course) so they dont blow up. Or, what kinda of resistor (from radio shack) i need to make string up a few (anything from 5-10LEDs). help!

 

heres a web link if you cant see my pic. or if its too blurry

http://www.superbrightleds.com/specs/hf-w2070.htm

 

The LEDs use 20mA of current each (nominal,) so wire them in parallel with a 510 ohm resistor in series with each LED. I'm not at work, otherwise I'd draw you the simple diagram. So, the resistor is in series with each diode (make sure you hook the diode up in the right way) - and then just wire up all of your diode/resistors in parallel.

You can wire up as many as these LEDs as you have resistors. You could wire up 50 of these and only pull a single Amphere.

The LED runs at 3.6V/20mA nominal.

- Project

 

see if this helps.

led calculator

just fill in the blanks and it will tell you what resistors you need .

 

The LEDs drop 3.6V apiece (typ). So 3 in series will drop 10.8V.

The cars voltage is ~14V.

So 14 - 10.8 = 3.2V drop across the resistor.

3.2V / 20mA = 160 ohms for 3 of these LEDs in series.

 

so i will need a 160 ohm resistor for a 3 led series?

 

also, radio shack has .25 and .5 watt resistors, which ones do i use?
I'm hoping i can use .5 watt, because RS sells a 150 ohm resistor.
For .25 watt, they only have 100ohm.


And one more dumb question, if I cant find a 160 ohm, can i wire a 100 and a 60 resistor in a series to = 160?

 

hooking up the diode the right way? u mean:

car 12 volt -->resistor-->LED-->ground

right?

 

The diode can only be hooked up in one direction. There is an anode (+) and a cathode (-) side to the LED. Make sure the anode (+) goes toward the battery +12V. Those surface mount LEDs that you're looking at have a notch on the cathode (-) side. That side should be towards ground. (Reference the image you posted.)

Hooking up the diode backwards will not kill it, but it won't light up as current flow is stopped.

 

Just use a 150 ohm resistor. 10 ohms is not going to hurt anything. If anything, the car's voltage is probably not quite 14 like I said.

1/4W is plenty, but 1/2W will work fine if that is all they have. (3.2 * .02 = 64mW for the resistor).