For any LED powering setup, it’s important to know how much current the LEDs are going to actually draw. If you do full brightness rainbow, only 1/3 of the max energy is used compared to full white color (in RGB strips, RGBW is another story).
A lot of patterns will typically not have 100% brightness for every LED, so power may be even less than that. OTOH, if you do go full white with all RGB lit up, it will draw quite a bit.
For example, 22 AWG wire can handle 7 amps for “chassis wiring” which is a conservative recommendation for non-bundled wires open to the air. 18AWG wiring would seem sufficient for 15A.
Another way to look at it is to calculate how much heat it is going to generate by power losses. 22 AWG is 16.14 ohms per 1000 ft, or 16.14mOhms for 1 foot. P = R * I^2. At 7A, its going to generate about 0.8W of heat (for each) across 1ft of area.
I was about to write a new post and I saw this one so i’m going to add a few details, and I have a question at the end, as i’m currently trying to calculate the minimum possible cable size for 1.40M of 144 LED/M SK6822 RGBW (5V) due to size constraints.
In my opinion there are major things to take into account that noobs like me don’t understand immediately:
Adressable LED use much less power than the maximum in general because it’s rare we maintain full white at 100% luminosity, and anything else than this uses MUCH LESS power
Actual power draw of a LED strip is always lower than the “rated” max power from manufacturer, unless you do power injection at 5V pretty much every LED.
Power injection does not really pull much more power than 6-7A for an extremity and 9-10A in the middle, because at this current, the voltage drop in the PCB of the strip is so massive that voltage on LEDs as you get further from the injection point drop, resulting in less power draw, therefore less Amps. I did a few measurements on my own i’m happy to share below.
AWG gauge is bullshit. Don’t get me wrong on this, i am NOT an electrician and i will not be responsible for any fire started, but it seems to be veeery conservative.
I did a few measurements on my own to try to see better:
Here are the conclusions I get:
obviously at these Amp I have massive voltage drop between power supply and the LED, so my strip is not even powered at 5V (therefore reducing its power draw)
1 injection point for 380 LED is not enough, as you can see it’s unable to draw enough power (6.3A max) and my white becomes yellow then orange after 2M (about 200 LED).
2 injections points are great and since they pull only 5A per point, it’s better for cables, strip and voltage drop
1 middle injection is a decent solution but then Amp are going up, pushing the cables to their limits it seems (can barely keep my hand on it)
however we can see i can run almost 9A in the factory wires that are the same as the ones on the JST connector, which is rated for 3A and the cables are AWG 22, rated for 0.92A for power transmission and 7A for chassis wiring. Obviously it’s not sustainable to run a long cable of this size at this intensity, but it shows than chassis wiring recommendation is probably enough to avoid cable fuse or isulation melting if you can control voltage drop of course. And keep in mind i used a PVC insulation cable, if you use silicone you can go even higher in temperature.
For my current project at the moment i’m planning to run:
1.40M @144 LED/m RGBW 5V SK6822
I have to run the power cable to the strip in a very narrow metal tube (4.5mm/ diameter). My maximum cable size would be AWG 18, or AWG 20. I have to run it through about 70cm.
This is for a floor lamp, so designed to be white at some times, full power = 43 W * 1.4 = 60 W ==> 12 A !!!
Considering AWG table, I should use AWG10 or AWG 11, which is insane. But if I consider voltage drop and chassis wiring, i’m pretty sure AWG 18 would work, it would just get quite hot.
This is true, and we mention this. As always, “it depends” is the true answer, but that is less helpful for newbies. When generalizing, we make safe recommendations that are less likely to lead a newbie to melting things or catching anything on fire on accident.
Addressable LEDs have constant-current circuits in them, so the same color should draw roughly the same current over the LEDs operating voltage range. That is, it should consume the same current at 4.5V as 5.2V. 20mA at 5.2V is more power (which is volts * amps) than 20mA at 4.5V, and this extra power is lost as heat. If you are observing lower current consumption, then the voltage is dropping below where the constant current regulation is the limiting factor and your LEDs are going to emit less light than neighboring LEDs with a higher voltage that can stay within regulation. The loss in light output may not be immediately observable, but once the voltage drops below the operating voltage of the blue/green LEDs you will notice color shift towards red, which has a lower operating voltage that blue/green. Some LEDs are better at handling this than others.
It isn’t entirely unreasonable – there are reasons behind these ratings, but it is conservative.
I think you may have missed this part in the original post:
10 AWG would be something around 55 amps for chassis wiring, not 12A. 18 AWG should handle your 12A. Just take into account that you will be generating heat on those wires inside your tube. If the metal allows heat to escape, you would probably be OK. The current capacity of those wires is going to depend on the heat transfer capability and ambient temperature, and heat tolerance of the wire and everything it’s comming in contact with.
How much heat and voltage drop?
Wire length: 70cm x 2. Count it twice since electricity has to travel both wires in the circuit.
At 18 AWG that’s 20.9428 ohms/km.
That’s 0.0293 ohms.
At 12A that’s a voltage drop of 0.35V. With 5.2V in, you would see 4.85V at the start of the LEDs.
0.35V at 12A is 4.2W of heat generation / power loss.
With 20 AWG you’d be looking at a fair bit more resistance.
20 AWG is 33.292 ohms/km.
0.0466 ohms for 70cm x 2.
0.559 volts dropped. 4.44V at the start of LEDs.
6.71W of heat / power loss.
I will go with the AWG 18 and see if it works. I can’t pass AWG 17 or less anyways. If I have to reduce the maximum luminosity for the LED to be safe then so be it !
