When running a lot of LEDs, it’s important to keep track of power usage. Individual LEDs don't get very hot or use tons of power, but they add up fast!
Each single 36mm RGB LED pixel can draw up to 120mA from a 12V supply. That means a strand of 20 can use up to 2.4 Amps. That’s a peak rate, which assumes that all the LEDs are on at full brightness. If most of the LEDs are kept dim or off (as when animating patterns), the average power usage can be 1/3 this or less.
We suggest a nice switching supply for driving LED pixels, such as our 12 Volt 5 Amp supply . For larger projects, a slightly modified ATX computer power supply can provide 10 Amps to power upwards of 80 pixels!
Since the 36mm pixels are powered by 12V but use 3-5V signaling, make sure you don't accidentally connect the 12V to your microcontroller — this will destroy it! For that reason, the power lines are separated out. Use something like a 2.1mm DC terminal block adapter so that you can directly plug in our 12V adapter.
The wires on the 3-JST SM connector are then connected to your microcontroller: black is ground, yellow is data and green is clock.