Hardwiring LED's

Calculation for resistor:

Car battery voltage: 12V

Resistor = (12V - 3V) / 0.03A = 300 Ohms

Power dissipated in the resistor:

So, it should be a 1/2Watt, around 300 Ohms resistor (doesn't matte if you don't find exactly 300 Ohms, can be higher BUT NOT LOWER).

Get that resistor from a local electronics supplier (or Radio Shack if you're too lazy to look for one and have extra $$$).

Hope it helps,

OK, let's say each LED is rated at 3 volts. So, you can only put 4 LEDs in series (3 times 4 is 12V), WITHOUT needing the resistor.

If you want to put more, than make series of 4 leds and put those series in parallel. EX: you want 8 LEDs, so make two groups of 4 LEDs and put those two groups in parallel.

Make sure you don't mess the polarity. In series, (+) of one LED goes to (-) of another LED. In Parallel, (+) goes with (+) and (-) with (-).

If you need to put 6 LEDs, then put 4 in series, then form a group of 2 LEDs and a resistor (value = [12-(3+3)]/0.02 = 300 Ohms), and put this group in parallel with the first one (**I assumed LEDs of 3 Volts at 20 mA).

If you're still confused, I can post a picture.

Alex

i understand what you are saying, but i am a visual learner and that would help out greatly

Whatever groupings you choose, try and make them even and the total count even, then you won't need different resistors for each group.

Ex: 9 LEDs is better in 3 groups of 3 than 2 groups of 4 and one single.

Hope it helps (and doesn't confuse you more, :D)

I don't agree with that picture very much, the first image would be ok if your LEDs matched ok.  The second one has the resistor on the negative side, you need the resistor on the positive side before the LED series.  The third picture has the LEDs in parallel with one resistor, this should be avoided in case LEDs don't have the exact same voltage, one will light and others not and then the one will burn out.

The second image is the most useful, but put the resistor on the other side of the series, on the positive side of the first LED.  The second most effective way is just one resistor and LED, then you don't have to connect the LED legs together if they are far apart.