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I bought it on Amazon, so it's pretty much a no-brand, no-specs, product, but the product page says 0.24W per LEDs and it has 300 LEDs, 72W (woa!). At 5V that would be 14.4A (double woa!).

It uses the WS2812B which I can see can consume up to 60mW per LED, so that would be 18A for the 300 LEDs. Ok, way more current than I expected.

I know I probably shouldn't be driving it at 100% and rarely all LEDs would be on at the same time, but if I look at what wire gauge I should use for 15A and 18A, it's AWG14 and AWG12 respectively. But when I look at what came already soldered on the strip, that looks like AWG24 (with a max current of 2.1A). Is this wire absolutely undersized for what the strip requires? Or did I mess up my calculations?

I don't mind re-doing the wiring, I just want to make sure I'm not getting it completely wrong.

enter image description here

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    \$\begingroup\$ The wiring along the strip is likely even smaller. It's just copper track on flex PCB. It may be impossible to use that with full current or the string will melt itself. \$\endgroup\$
    – Justme
    Apr 1 at 12:07
  • \$\begingroup\$ @Justme: so, all LED strips would catch on fire if you run them at 100%? something doesn't add up for me here. \$\endgroup\$ Apr 1 at 12:40
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    \$\begingroup\$ We don't know what you bought and how much lies you were told on sales page. Also if the wire is short, and you allow more voltage drop and higher temperature, you can define the max current for some wire. We don't know how you ended up thinking the wires are able to carry only up to 2.1A. \$\endgroup\$
    – Justme
    Apr 1 at 12:50
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    \$\begingroup\$ AWG24 wire typically has a maximum current rating of around 2.1A. It is far below the 14.4A your LEDs might draw at full brightness. \$\endgroup\$
    – liaifat85
    Apr 1 at 16:01
  • \$\begingroup\$ Are you sure that's copper wire not aluminum? \$\endgroup\$
    – user71659
    Apr 1 at 21:51

3 Answers 3

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The 60 mA per LED is the max rating, not a typical current draw. The strings that I have measure about 32 mA per LED. You should measure yours. PWM at a lower percentage and extrapolate.

For a long string, you are expected to apply power to both ends.

300 * .032 = 9.6 A. If you power both ends, then each end will need 4.8 A. The wires on my strips are 22 AWG. The table that I use says that this is good for 7 A.

If you have long wires, the voltage drop will be the limiting factor. Run some calculations. The chips have constant current drivers that work down to 4.3 V or so, but don't get close to this, allow some margin.

Conclusion: The short leader should be fine. You may need to use larger wire on the connecting cable.

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24AWG wire has a cross section of 0.2050 mm square.

If we generously assume your LED strips have a 4 mm wide positive and 4 mm wide return trace using 1 oz copper, their cross sectional area is 0.140 mm, which is equivalent to 26 AWG.

Since your feed wires are have a larger cross section than the strip itself, the resistance of the strip itself will dominate and (at least for the couple inches you show) they're thick enough. You also won't get anywhere near 18A though with a single feed line due to the resistance of the strip (probably more than 0.134 ohms per meter). You'll need to inject voltage at both ends and possibly the middle of the strip to get that much current.

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Minimum current consumption with one color on is approximately 1mA. Not only connected wires but PCB conductors cannot carry big current. Also drop voltage on PCB conductors could be taken in account. If you need more, just add power wires in the middle. Or choose proper pattern.

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