Correctly powering NeoPixel projects — especially larger ones as the pixel count gets into the hundreds or even thousands — sometimes seems like a mystical dark art. The next few pages will help make some sense of this.

The confusion arises in that folks often want hard numbers. In the code domain, memory and bits are finite and digital; it’s simply a hard fact whether X number of pixels can fit in Y amount of RAM.

Power isn’t like that; it’s analog. We know some possible per-pixel minimums and maximums, and some guiding rules of thumb, but it never works out into firm X-into-Y numbers. Doing this well requires some conceptualizing and some testing and measuring, perhaps on a limited smaller scale to start.

These other guides can provide some insights:

• Adafruit NeoPixel Überguide — especially the Powering NeoPixels page
• Sipping Power with NeoPixels
• 1,500 NeoPixel LED Curtain with Raspberry Pi and Fadecandy — especially the Power Topology page

Some essential concepts can be distilled as:

• Every NeoPixel that’s powered, even if “off” (set to color 0,0,0), draws a minimum amount of current to run the internal logic. The exact amount varies a bit among different WS2812-compatible LEDs, but a reasonable rule of thumb is “about 1 milliamp per NeoPixel.” That is, 100 “off” NeoPixels might use around 100 mA of current. It’s usually a bit less, but 1 mA provides a safety margin and keeps the back-of-envelope math simple.
• The maximum current per pixel (lit white at full brightness) also varies among devices, but a common rule of thumb here is 60 mA per RGB pixel, 80 mA for RGBW. Again, reality will often be somewhat below these values, but they’re easy and provide a comfortable margin.
• The actual current will be somewhere between these two values, and it just isn’t possible to get an accurate prediction, especially with lots of animation. The “Sipping Power” guide mentioned above explains how to choose colors and program animation to skew more toward the minimum power estimates.
• The current rating of any conductor or power source — a length of wire, a battery, a copper PCB trace, a USB socket — is a comfortable estimate based on continuous current draw in typical setting (e.g. in open air). Most can deliver more current for brief periods, as long as it balances out over time. In a sense, any conductor is like a fuse, and the key here is to keep it in the safe zone. It’s about thermal equilibrium.

There are instruments that can help in determining power draw; most multimeters have a current measuring mode, a decent workbench power supply will show actual current drawn, and so forth.

Caution with multimeters: it’s common for these to have a fuse that trips at some number of milliamps or a couple amps at most. Check the manual. Large projects will surely exceed this rating, so it’s often prudent to first build a small section of your design, measure and iterate on that, then scale up to the full project.

If you don’t yet have these tools, a simple test is to feel if the board or any wires start getting uncomfortably warm to the touch. If so, the pixels are pulling more current than the conductors can safely supply. Stop immediately and plan more robust power distribution.