Trying to calculate current draw for RGBW LED strip



  • Got a great deal on a spool of adafruit's analog 12v RGBW LED strip (https://www.adafruit.com/product/2439?length=1), so figured it would be great to connect to the duet wifi's duex5 expansion board, but trying to figure out how long of a strip i can safely run as there's no watt/meter spec available (i've found the 24v version of the LED strip here: https://www.shiji-led.com/Product/view/id/1004.html which appears identical except longer sections of 6 LEDs, vs the 12V having shorther 3 LEDs per section). the resistor codes appear to be 301 (marked as Red) and 151 for the other 3 (Green, Blue, White), was wondering if that would be enough to calculate watts/meter to not overload the 1.5amps available on the duex5 fan connector



  • @mikebridge Adafruit's documentation is here:
    https://learn.adafruit.com/rgb-led-strips/current-draw
    You could also disable an unused heater output to drive the LEDs if the 1.5 amp fan connector limit is an issue.



  • these are RGBW, not RGB, so I'm using that page as a benchmark, but just wanted to confirm the values if possible as there's no spec sheet for this specific item form them.



  • @mikebridge Have you contacted Adafruit? Their support is pretty good.



  • @mikebridge Interesting. I should have looked at their video before responding. I am curious how you will connect this to get all four colors? I assumed that all LEDs would have to be lit to get white, but maybe only the white LED comes on for white?



  • @ayudtee said in Trying to calculate current draw for RGBW LED strip:

    @mikebridge Interesting. I should have looked at their video before responding. I am curious how you will connect this to get all four colors? I assumed that all LEDs would have to be lit to get white, but maybe only the white LED comes on for white?

    there's 4 led's in each 'package' (and 3 of those per 5cm section, so a total of 20 sections per meter), R G B and a dedicated W led (in this case, a 'soft white').

    If I'm using Ohm's law correctly, each segment with all LEDs (12) lit would be using 280mA which seems REALLY high
    12v/300=.04, 12v/150=.08, for .04+3*(.08)= .28


  • administrators

    It sound to me that if you light all 4 colours together, the current draw will be about 80mA per 5cm for the 12V version, and 80mA per 10cm for the 24V version.



  • 280mA does seem too high for a (3) 4 color LED segment. If adafruit's RGB strip's LEDs have the same values as their RGBW strip and each color LED uses 20mA per segment, then each 4 color - 3 LED segment would use 80mA.



  • it does appear to be the case that its ~80mA per RGBW section (20mA*4), with 20 sections per meter for this product.
    Would the amps drawn be linear w/ the PWM range i.e. full 20mA per section at S255, but 2mA at S25.5?


 

Looks like your connection to Duet3D was lost, please wait while we try to reconnect.