Need help sorting out wire gauge calculation for powering LED strip

Thread Starter

Aleksey Shurtygin

Joined Dec 21, 2018
62
Hi guys!

Can anyone help me sort out what I am doing wrong?

I am planning to setup Addressable RGB LED lighting and run it across ceiling in the living room with the perimeter length of about 20 meters (or ~60'). So with basic math figured out that I will need 4 of these strips (https://www.amazon.com/gp/product/B07QGD3YHH) and planning to run in parallel.

upload_2019-5-20_15-59-48.png


I used their specifications to calculate power needed to run it and ended up with ~25 Amps. According to specifications the strip is using 14.4 W/M. Single strip is 5 meters so total power usage for whole strip should be 72W. Assuming voltage is 12V I should expect that this strip will draw total of 72W/12V=6A. And now assuming I connect them in parallel it will draw total of 6A * 4 = 24 Amps.

So far everything seems to be ok until I started to calculate wire gauge required to power these. And for some reason numbers do not add up or they just feel weird and/or strange. So I really need your help to try to figure out. Here is how I do my calculations.

Assuming I want to power the farthest strip I would need 5m * 3 strips = 15 meters of wire to power the last one. According to this site https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html (and many others) and considering the Amps and length, I should really be using 4 AWG wire. According to several other sites 4 AWG wire should be about 5mm in diameter. Which is a bit bizarre to run it so thick. So, I thought, ok, maybe its just that I never had to deal with this and decided to accept it and go with it for time being.

But here is where things start to get confusing and interesting. If I look at the LED strip itself I see they use 20 AWG power wire. If I perform same calculations I end up with at least 12 AWG (not 20) - 6A @ 5 meters. When I did try to power it, it worked fine without a hint at heating up. And when I measured voltage and current I got ~11.9V and 3.12A - running all LEDs in white at full brightness. This tells me that either manufacturer is misrepresenting their numbers, or running under some assumptions that really never happen or I am calculating something incorrectly.

And now the question (drum roll)... what the hell am I missing?

Anyone got any hints, thoughts, ideas?

Thanks!
 

Zaishens

Joined May 20, 2019
28
I think the 72W/6A is if all individual leds on one chip would be on, the controller makes a mix of colours and only turns on the leds partially. So unless you trick the controller, you can't get much more than the measured 3.12A out of one strip. I hope this helps.
 

Thread Starter

Aleksey Shurtygin

Joined Dec 21, 2018
62
I think the 72W/6A is if all individual leds on one chip would be on, the controller makes a mix of colours and only turns on the leds partially. So unless you trick the controller, you can't get much more than the measured 3.12A out of one strip. I hope this helps.
That would be reasonable explanation. The only problem is that I used Arduino to turn on all 300 LEDs at full brightness white (or at least its what I would expect). I would also expect that this would turn on all 3 colors completely. The only thing is that I am not sure whether this is actually the case and there is something else that needs to be done to get it to full brightness.
 

Zaishens

Joined May 20, 2019
28
That would be reasonable explanation. The only problem is that I used Arduino to turn on all 300 LEDs at full brightness white (or at least its what I would expect). I would also expect that this would turn on all 3 colors completely. The only thing is that I am not sure whether this is actually the case and there is something else that needs to be done to get it to full brightness.
I think what you got is the full brightness for white, the controller (led chip/driver itself, not the micro) will not turn all three fully on if you request white. First of all, white is not 3 equal parts of RGB, and secondly, that would be too much power for the chip/driver. Each individual colour is proabaly maxed at an average of 2A (when it's the only led on) making the 6A "max".

Can you turn all colours on individually to the max instead of white?
 
Last edited:

Thread Starter

Aleksey Shurtygin

Joined Dec 21, 2018
62
I think what you got is the full brightness for white, the controller (led chip/driver itself, not the micro) will not turn all three fully on if you request white. First of all, white is not 3 equal parts of RGB, and secondly, that would be too much power for the chip/driver. Each individual colour is proabaly maxed at an average of 2A (when it's the only led on) making the 6A "max".

Can you turn all colours on individually to the max instead of white?
This is RGB model and not RGBW. It does not have separate white LED. So, it exactly will turn all three colors to get a while color and I do that in Arduino by calling leds = CRGB(255, 255, 255); which basically sets all three colors to its maximum value. However, maybe internal logic limits a current when all 3 colors are on, not sure. I will check it tomorrow when I get replacement power supply to try to turn on individual colors separately and see what the current would be.
 
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