Led strip current consumption

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I asked a similar question in one of my previous posts but I did not get a reply so I am trying again.
I have made lamp with WS2812B led strip. There are 120 LEDs in the lamp. It works fine currently with a 10A 5V regulated power supply.
I have measured the current that it uses at full brightness and noticed that it only draws 3.8A. I wonder why this is so different from the theoretical calculation, assuming a 60mA consumption per LED. Even assuming that the max consumption is 50mA per LED (this would give 6A for 120 LEDs) 3.8 is still much less than that. Now I want to make sure I am not missing something before changing the PSU to a 5A one (I have one available, which is smaller and more convenient in this case).
Thanks!

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All LEDs at full-brightness white? All 3 colors at maximum?

And you've got the voltage "injected" about every meter so so your not getting voltage drop through the length of the strip?

There are always part tolerances and I assume 60mA is the maximum ("worst case" so you are always safe if you base your power supply on that). But I wouldn't expect to be almost half!

...The power supply should have some tolerance too, but in the other direction. A 10A power supply will usually be OK at 10.1A, etc. But it's only guaranteed to 10A and it's "good practice" to "derate" it for some safety margin.

On the other hand, with addressable/dimmable LEDs you are usually only occasionally running them all at full brightness and you can usually get-away with "cheating" a bit. But it's not recommended...

It should be OK. You've still got plenty of safety margin.

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See this comment at
" Pololu - Addressable RGB 60-LED Strip, 5V, 2m (WS2812B).

We tested the current draw and voltage drop of some LED strips by setting all the LEDs to full brightness, and these were the results:

  • The 30 LED 1 m strip drew 1.5 A and had a voltage drop of 0.2 V.
  • The 60 LED 2 m strip drew 2.9 A and had a voltage drop of 0.8 V.
  • The 150 LED 5 m strip drew 4.1 A and had a voltage drop of 2.0 V.
  • The 60 LED 1 m strip drew 3.0 A and had a voltage drop of 0.6 V.
  • The 120 LED 2 m strip drew 4.7 A and had a voltage drop of 1.4 V.

As the voltage reduces with each LED, the current will also reduce.

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4

Would this data support Neopixels require less current? Not 7.2A per 120 pixels for 20mA per Neopixel-LED, rather 4.7A per 120 pixels for 15mA per Neopixel-LED?

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yes, or at least, I believe so. I can post my code if needed but I did not limit the brightness in my code. I am using potentiometers to set hue saturation and value and with everything at max I got 3.8A. I will check again.

yes I have injected voltage at the end of the strip.

Apparently I do, but as you said it is a bit strange to have half ot the Amperage expected

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Thanks I will have a look. will also retest everything with a basic code, just in case something in my code is limiting the brighness without me realizing

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I tested it again with this simple code:

#include <FastLED.h>


#define NUM_LEDS 120
#define LED_PIN 11

CRGB leds [NUM_LEDS];
void setup() {

  FastLED.addLeds<WS2812B, LED_PIN, GRB> (leds, NUM_LEDS);
  FastLED.clear();  
  FastLED.show();

  delay(1000);
  
  FastLED.setBrightness(255);  
  for (int i = 0; i < NUM_LEDS; i++){
    leds[i] = CRGB( 255, 255, 255);
  } 
  FastLED.show();
}
void loop() {}

the current drawn is actually 3.50A
this is with 120 LEDs (WS2812B) and 10A 5 V PSU....
I think I can safely use a 5A PSUgiven this result...

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There are probably quite a few people who manufactures the WS2812B but according to this data sheet from Worldsemi, it's only 12mA per LED, 36mA for all three.
So I guess 3.5A is in the ballpark.
2006151006_Worldsemi-WS2812B-B-W_C114586.pdf (609.9 KB)

1 Like
9

Thank you!!

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You are welcome.