2 LEDs don't draw 2x 1 LED mA?

[kastoria]

I have the 12 pixel Neopixel ring. I know the rule of thumb is max 20 mA per LED or max 60 mA per pixel. I know that brightness and power draw are not linear. I was trying to see how much power the ring would actually draw at different brightnesses. I'm using the Adafruit Neopixel library. I'm measuring amps between the strip's negative lead and common ground. This is all getting powered from the board itself off USB power. 240 mA would blow out my uC for sure so I think my measurement is accurate.

I found that running 1 pixel with 1 LED at a time full intesnity:
- r, g, b all showed ~15 mA each
- r + b showed ~ 25 mA
- r+g+b showed ~35 mA

I would have expected that r+g+b would be 45 mA. But this is still way under the estimated 60 mA max draw.

When I light up 2 pixels 1 LED at a time the values don't add up:
- r, g, b showed ~25 mA each, not 30 mA

As I turned on more LEDs on more pixels, the expected power draw reduced significantly.
- 4 pixels at max brightness (r+g+b) was only drawing ~100 mA, no where close to the expected 240 mA

Does the Adafruit library have some kind of power limiter built in?
Do the neopixels somehow have a power limiter?

Suggestions?

[adafruit_support_bill]

I suspect there is some resistance in your power path that is limiting the current. If you post some photos showing how you have everything hooked up we can take a look.

[kastoria]

There were actually several issues that I managed to root out. None of them were behaviors of the Adafruit neopixel library or the laws of physics in my hobby area.

I simplified my circuit down and there was an extra path for the current to down. It is also possible that power drawn by the uC was partly contributing to my current readings. Between the two that seems to have been the cause of the weird measurement errors.

[adafruit_support_bill]

Good to hear you figured it out. Thanks for the follow-up.