Connecting LED's to 12 Volts
by: Andrew Krause
Lots of people are using LED's for custom applications. LED's, because of their Solid State nature, last several hundred thousand hours longer than light bulbs, and are much brighter while consuming less power. The problem is, most LED's come in voltages lower than 12 volts. Using an LED in a car is simple, and has many applications. All you need is a simple resistor.
Which resistor is the problem. There are several different voltages. This means a little bit of math is in order. When you buy the LED that you want to use, look on the back of the package. There is a little list of numbers called the "Electro-optical Characteristics". The two numbers we're interested is is the "Forward Voltage" (This is the amount of voltage the LED works best at), and the operating current (the amount of current the LED will draw).
There are two ways you can wire your LED's up.
First, you can divide the supply voltage (12 volts) by the LED's operating voltage. The number you have is the number of LED's you can wire in series and connect to 12 volts.
The better method is to calculate the resistor you will need. To do this, you first subtract the LED's forward voltage from 12 volts. Then, you take the result, and divide that by the LED's operating current. The number you have left is the number of ohms of resistance you will need in order to safely connect your LED. If you get a number for which you don't have a resistor, you can use slightly higher resistor. If you don't even have one close, you can use resistors in combination to get the proper value.
When wiring your LED, it is important to observe polarity. Often, the positive and negative legs are different length. The package will show you the polarity. Wire your resistor in series with the LED, on the positive leg.