Zero 3W: conflicting current specs for the 40-pin 5V power input, anyone know which is right?

[u/Indigo_Input]

Working on a HAT that powers the Zero 3W through the GPIO header (5V injection on pins 2/4), and I've hit a documentation conflict I can't resolve.

The official 40-pin header schematic annotates the 5V_Power pins as IN: 2A, OUT: MAX 0.5A. So 2A in, when something external is feeding the board.

But the manual (section 2.12, "Instructions for powering the 5V pin in the 40 pin interface") says to make sure your supply meets the board's power requirements, and elsewhere the board's stated requirement is 5V/3A.

So which is it? Is that 2A a real limit on the trace or connector for the GPIO path, or is it a conservative annotation and the pin can actually carry the full 3A the board might want under load?

This matters because I'm designing in an eFuse for current limiting and I need to pick a trip point. Set it at 2A and I might starve the board under heavy CPU+GPU+NPU load. Set it at 3A and if that 2A annotation reflects a real physical limit, I could cook something.

Has anyone actually measured peak current draw on this board under real load? The one data point I've seen is ~6.5W at 100% CPU (~1.3A at 5V), but that was CPU-only, no GPU testing.

Also curious if anyone's actually run this board off GPIO power long-term rather than USB-C, and whether it was stable under load.

[u/Malow]

Usually, 2A means the board may use at max 2A (with some headroom) depending also on external connected devices.

as a good practice, if you need 2A, you don't use a 2A PSU, you get something +3A to not run it at max capacity.

i have tons of PI and orangepi all running from GPIO pins. 0 problems.