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I have an Arduino Uno. I bought this LED strip: https://www.amazon.com/gp/product/B019DYZNO6/ref=oh_aui_detailpage_o08_s02?ie=UTF8&psc=1

Starting initially using FastLED library. When I tried to set the entire strip to white (255,255,255), it was coming out red. Any color close to white was coming out red.

I thought maybe there was an issue with the library, so I tried the neopixel library. Same thing until... If I just set one pixel to 255,255,255 and don't set any other, it comes out white! If I set about 10 pixels, they still look white. As I set more pixels, they start to loose their whiteness and become red.

I want to say that maybe this was a power issue... but I tested this both when it was running off my PC and running standalone with a power supply (supplying 5V).

Any suggestions?? I also thought that maybe it's a bum strip, but I also bought https://www.amazon.com/gp/product/B01AG923GI/ref=ask_ql_qh_dp_hza and did the same experiment, and am getting the same results...

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    How much current does your external power can supply? These LEDs can be very power hungry. For my strip each LED uses 30mA when completely white. This would result in 4.2A for a 140 LED strip like yours
    – chrisl
    Commented Mar 19, 2018 at 23:45
  • do you have the recommended capacitor and resistor between the strip and MCU?
    – dandavis
    Commented Mar 20, 2018 at 7:29
  • For future searchers, this same problem can also give a Green colour when trying to set the neopixel grid to white.
    – Jethro
    Commented Jun 22, 2018 at 10:14

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According to https://learn.adafruit.com/adafruit-neopixel-uberguide/powering-neopixels a Neopixel can consume 60 mA at full brightness white.

Each individual NeoPixel draws up to 60 milliamps at maximum brightness white (red + green + blue). In actual use though, it’s rare for all pixels to be turned on that way. When mixing colors and displaying animations, the current draw will be much less. It’s impossible to estimate a single number for all circumstances, but we’ve been using 1/3 this (20 mA per pixel) as a gross rule of thumb with no ill effects. But if you know for a fact that you need every pixel on at maximum brightness, use the full 60 mA figure.

So your 144 Neopixels would require 8.4 amps. You would need a pretty solid power supply to supply that much.

One way of confirming that would be to measure the voltage in to the Neopixel strip (at the strip end) when it is displaying all white. I'd be surprised if it measures 5V.

The Amazon page you linked says:

Voltage: DC 5V

Power: 0.3W ± 0.01% per LED

That agrees with the figure of 60 mA (0.060A * 5V = 0.3W)

To put it another way, your power supply would need to supply 43.2W (144 * 0.3W). None of the bench power supplies I have here can put out 43W (or 8A), nor any of the wall-warts. You may have a really massive one, but you haven't specified what sort of power supply you are using.

I run them with a power supply (one that is working as expected, but still have it connected to the PC/USB?

Yes, there is a technique for doing that (similar to powering motors etc.).

Powering Neopixels

  • You have one low-current supply to the Arduino (this could be your USB port even).
  • You have a high-current supply to the pixels/motor/whatever. This would require thicker cables.
  • You connect the grounds of both supplies so that they have a common ground reference.
  • The data line (the pixel information) is sent from the Arduino to the Neopixels

The one power supply can do both roles, just connect the wires together at the power supply end (this automatically connects the grounds, of course).

This way, the heavy-duty current does not go through the Arduino board.

If you are using the USB port for logic power you still connect the grounds like this:

Powering Neopixels with USB for logic

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  • I'm using the power supply recommended by the LED folks on the Amazon page which is a 5V, 10A. amazon.com/gp/product/B01M0KLECZ/… Now... I haven't taken out my multimeter and doublechecked that that's what I'm getting out of it... but problems with current make sense.
    – adeena
    Commented Mar 20, 2018 at 9:47
  • Sounds reasonable, but at that current you might be losing voltage over the wires. Measuring the input to the strips, at the LED end would confirm that.
    – Nick Gammon ♦
    Commented Mar 20, 2018 at 10:13
  • You might need to apply power to both ends of the strip (if that is practical) because there might be a voltage drop over the length of the strip itself. Especially if the white colour deteriorates progressively (ie. white at the start, not so white at the end).
    – Nick Gammon ♦
    Commented Mar 20, 2018 at 10:16
  • I just measured the output voltage of the supply... getting less than 3V. :( My multimeter doesn't seem to be working for Amps. So my next question... can I run this strip of light off the Uno when it's connected to my PC? I'm guessing not since there's only a 5V and 3.3V output. I did try with the 5V and am also getting the same issue... white for a few pix, no white for lots of pix.
    – adeena
    Commented Mar 20, 2018 at 10:17
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    The strip needs 5V to operate correctly. With 3V it won't work as intended. Also you cannot drive your strip from your PCs USB, since they only provide up to 500mA, so far not enough current for the strip when turned on. In doing so you can also damage your Arduino or USB port of the PC. When the LEDs are of it is possible. Try measuring the voltage output of your power supply without anything connected, to ensure that it really outputs 5V. If not the seller send you a wrong product.
    – chrisl
    Commented Mar 20, 2018 at 14:19

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