Neopixel Power Supply

[DrGonzo]

I'm a bit new to the whole arduino/LED programming scene. I am wanting to make a table for my buddy and we need 6 meters of neopixel lights to go around the perimeter of the table. In the product description it says only one meter is 5v, 3.5 amps when at full white brightness. Am I correct to assume that if I have 6 meters of lights I will need a 5v, 25 amp power supply to run the whole strip correctly? So I would have my power supply to my LED's in addition to a power supply to my arduino.

[adafruit_support_mike]

That's a correct maximum-case estimate.

In practice you can usually get away with using less current.

The human eye responds to light logarithmically, meaning we see ratios better than absolute light levels. "Twice as many photons" produce the same visible change, whether you're going from 10 photons to 20 or 1 million to 2 million (the visible difference in "twice as much light" is barely noticable BTW). Perceived brightness also depends on the ambient light levels, which is why car headlights are almost invisible during the day but can be blinding at night.

Color mixing also reduces the amount of time current flows through a given LED, so that has an effect on your working current level too.

I'd suggest starting with a single strip and playing around with it to get a feel for how it behaves. Work out the display patterns you like and measure the power consumption for the way you'll actually use the strip.

WRT choosing a power supply, there are a couple of options. You can use a single high-power supply and make connections every meter or so along the strip (we do recommend making at least one connection per meter to avoid line losses), or you can use separate power supplies for each strip. As long as the GND rails are all connected, the control signals will flow properly, and the VCC rails can be independent of each other.

[DrGonzo]

Thank you so much. I have ordered one meter and am currently waiting for it to come in. What exactly do you mean by making connections every meter? Soldering/extending the wires to the main power supply for each meter? and if I had to get a power supply for each meter would that mean I would need 6 different power outlets as well?

[adafruit_support_mike]

You can use a single power supply that's strong enough to run all the NeoPixels in your system, or you can use a set of smaller power supplies that are strong enough to run a particular segment. There are arguments for and against either option, and the best answer depends on things like layout, complexity, length of wiring, etc.

With a single power supply, you'd want to connect VCC and GND wires to the strip about every meter, then run all those wires back to the supply. The effective resistance of the wiring will be much lower than the effective resistance of the LED strip, so pixels near the second VCC-GND pair will find it much easier to get power from those wires than from the wires a meter away.

The connections for multiple power supplies would be the same, but you'd connect each pair of VCC-GND wires to its own power supply.

[hrheingold]

How can I buy 2 and 3 meter neopixel strips? On the shopping cart and your catalog I see only how to buy multiple one-meter strips.

[Franklin97355]

How can I buy 2 and 3 meter neopixel strips? On the shopping cart and your catalog I see only how to buy multiple one-meter strips.

You can buy 1 meter strips or an entire reel (5 meters)

[hrheingold]

Thank you for the swift reply. However, I do not see 5 meter reels in your catalog: https://www.adafruit.com/category/168

[adafruit_support_bill]

It you put more than one in the quantity field, you will get a continuous strip - up to the length of a full reel. Our current supply comes in 4 meter reels.

https://www.adafruit.com/products/1138
"They come in 4 meter reels with a 2 or 3-pin JST SM connector on each end and separated power/ground wires. These strips are sold by the meter! If you buy 4 meters at a time, you'll get full reels with two connectors. If you buy less than 4m, you'll get a single strip, but it will be a cut piece from a reel which may or may not have a connector on it.

[hrheingold]

As always, I appreciate the swift support. I suggest that you add language to disambiguate the ordering -- it isn't entirely clear that you can order multiple meter strips and not just multiple one meter strips.