Required Resistor for LED 2

[InMFG]

Electrical is not my speciality, so please help me out on this one.

I am looking to purchase this LED (

http://tinyurl.com/3v48f9p).

I have a 12 volt DC power source. What size and type of resistor do I need for this LED?

Thanks.

 

[Skogsgurra]

That seems to be one of the first generation LEDs. Are you sure it is the one you really want?

Anyhow: R = (supply voltage - 2)/0.02 = 10/0.02 = 500 ohms. Wattage Is 10*0.02 = 200 mW or more.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[VEBill]

Confirm 12vdc power supply is actually 12.0 or 13.8 (automotive standard). Assume 12.0...

12.0 subtract 2.0 volts, forward voltage drop of LED.

Leaves 10.0 volts to be dropped across resistor.

Diode spec sheet says 20 mA and I've confirmed max is 30, so 20 is good.

R = V / I = 10v / 20mA = 0.5k ohms (kilo and milli cancel) = 500 ohms
Standard values are 470 and 560 ohms, but you might find 510 ohms.

http://www.elexp.com/t_eia.htm

(you can multiply by tens).

Power on resistor?
P = V * I = 10v * 20mA = 200mW
1/4 watt a bit close, use half watt.

 

[MikeHalloran]

If the LED is mounted, say outside, far forward on a fender, 20mA may be ok.
For in-dash use, even first generation LEDs are terribly bright at 20mA, while easily visible at night at 2mA.
Consider an adjustable resistor, or slaving the indicator to the instrument light supply.


Mike Halloran
Pembroke Pines, FL, USA