Hey everyone,
I have the following LEDs and are trying to figure out what size resistor I need. I am wiring them in parallel from my vehicle (12 volts).
a.) 12,000 mcd, 1.8-2.2 volts, 24mA
b.) 5,000 mcd, 1.8-2.2 volts, 24mA
Do I assume 12 volts when calculating since the car really operates at 9-14 volts? Also, should I use the 1.8 or 2.2 when making the calcualation?
If anyone can help answer my questions and give me their opinion on what size resistors I'll need, I'd appreciate it.
Thanks.
I also wanted to mention that I don't necessarily need to get all of the brightness out of the LEDs. If I can run a different resistor and have them a little dimmer, that's fine too.
Just to be safe, a 1000 ohm resistor will safely light up any LED I have run across. I have never seen any damage done by using a 470 ohm either.
depends alot on the LED but i normally use 470. i use 1000 too but i also notice i can always use a 470 on the same resistor and its a little bit brighter.
Since both LED's have similar specs it makes it much easier. Use 2V as a reference for each LED.
Assuming a nominal voltage of 12V from the battery, the voltage drop across the resistor should be 10V. Using Ohm's law, R=E/I. R = 10/0.024 = 417 ohms. The closest standard resistor is 430 ohms.
With a nominal battery voltage of 14V, voltage drop across the resistor should be 12V, so R = 12/0.024 = 500 ohms and the closest standard resistor is 510 ohms.
Depending how safe you want to be, you can a resistor is small as 430 ohms. A higher resistance would result in less brightness.
If you decide to wire the LED's in parallel, you only need one resistor.