Which gauge wire should i be using?


New elf
Dec 4, 2019
This thread is extremely helpful but I'd like to kindly ask for a bit of hand-holding because I've never done this calculation before.

Let's say I have a 2.5m strip of of 60/m SK9822 LEDs (so 150 LEDs, aprox 9A max draw altogether)
My controller is Advatak MKII Long Range, but I don't think that's relevant.
I am going to inject power every 50 pixels, hopefully from a single 5v60a Meanwell power supply. So I *think* that means there will be 3A load on each cable.
I'd like to use 18awg copper speaker cable from the power supply to the strip, through 2.1x5.5MM barrel jack connectors.
How do I calculate the maximum length that speaker wire can be?
I've read elsewhere that anything over 5% voltage drop will cause problems. So I need to stay under 0.25V drop.

Let's try 1 meter:
18awg = 0.021 ohms/m = 0.021 x 3a = 0.063 voltage drop = ACCEPTABLE

Let's try 2 meters:
18awg = 0.021 ohms/m * 2 meters = 0.042ohms x 3a = 0.126 volts dropped = FINE, RIGHT?

But this isn't factoring in the resistance in the LED strip itself. How do I calculate that? Do I treat it like XXawg wire?

Is this accurate? Anything I'm misssing here? Or any glaring mistakes in my proposed setup?

thanks in advance.
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