Wiring question

[manofthehour]

I am wiring two LEDs in a serial connection (25mA 3.3V) and know I need a resistor but I have no idea how big and what kind of resistor lol. Any help?

Like this? (except it is only one resistor)

[Boon]

If it's going in a car you'll want to allow for 14.4v input for when the car is on.

With the LEDs in series you're dropping 6.6v so you need to kill another 7.8v

Current is 25mA or 0.025A

V=IR

7.8=0.025 * R

R = 312 ohms - so you're probably good with a 330 ohm or 2 150 ohms in series.

7.8v dropped at 25mA = 0.195w so you'll probably be fine with a 1/4w resistor, though use a 0.5w to be safe if you can get them easily.

[manofthehour]

If it's going in a car you'll want to allow for 14.4v input for when the car is on.

With the LEDs in series you're dropping 6.6v so you need to kill another 7.8v

Current is 25mA or 0.025A

V=IR

7.8=0.025 * R

R = 312 ohms - so you're probably good with a 330 ohm or 2 150 ohms in series.

7.8v dropped at 25mA = 0.195w so you'll probably be fine with a 1/4w resistor, though use a 0.5w to be safe if you can get them easily.

I used a 270 ohm 1/2 watt resistor with a 5% tolerance... got 5 of em from radio shack for $.99 but discovered the LEDs I got were 5mm and they were slightly too big so I got the 3mm which are 20 mA (which yes is milli so .02 A) and 3.0V and its a 12V input. Radio shack surprisingly has a butt load of this type of stuff... thanks for the help tho I actually remembered to use some of the physics I learned this year to help me out lol. Thanks though! However I did wire two of the 5mm ones in series to a small 12V battery I have and used one of the resistors mentioned above and it worked fine they are really bright lol.