# How to get the DC power I need

I'm building a bookcase, to which I'd like to add lighting controlled by an Arduino or Raspberry Pi. I've gotten most of the software bits figured out, but I'm not sure I've gotten the power part figured out as well as I need to. I'm using Adafruit's NeoPixel LED strip for the lighting.

Each shelf is be 31 inches wide, there will be 8 shelves total in the bookshelf. I can't connect all the shelves in series, because the product documentation tells me each "strip" of LEDs can be no more than 5m long, so I'm planning on having each pair of shelves as one "strip", for a total of four strips in parallel. By my rough calculations, I'll end up with ~ 96 LEDs per series (48 per shelf times two shelves per series), requiring almost 6A of maximum current draw per series.

First, am I at least in the right ballpark with these power requirements, or am I so far off as to need professional electrical help?

Second, if these numbers are correct, should I try to find a single 24A 20VDC power supply, or should I instead use four (4) 6A 5VDC supplies? What are the main drivers for choosing one over another?

• I hope you won't have any valuable books on your bookshelf - I can imagine the pages/covers yellowing/browning a fair bit with 4 30 watt power supplies driving all that power into a gazillion LEDs. Commented Dec 12, 2016 at 14:59
• A single 24A 5VDC supply might make sense, but 24A 20VDC? You'll need a voltage divider (or center taps) to get the 5V you need to drive the strips. And then if one strip goes out, the divider will only approximately even things out for the others, at which point they'll all be overvoltage. Was "20VDC? a typo?
– John
Commented Dec 12, 2016 at 15:01
• @John - That's why I need the help - I figured I'd need 20VDC since I'd be running 5VDC per series * 4 series in parallel. I've got high-school-student level experience (at best) with this type of thing, though I can write the software to drive the Arduino easily.
– John
Commented Dec 12, 2016 at 15:04
• @Andy - I don't plan to have the LEDs at full power. I might drop back to adafruit.com/products/1460 (30 LEDs/m vs 60) if the 60LED/m strip proves too bright.
– John
Commented Dec 12, 2016 at 15:06
• When you plug in two lamps to a standard outlet...they're in parallel. Do you need 230 V instead of the usual 115V? (Assuming US here...) No. You need more current, but not more voltage.
– John
Commented Dec 12, 2016 at 17:12