kristaholle36 wrote: ↑
Fri Mar 29, 2019 6:27 am
The external output port has a self-recovery fuse to prevent the raspberry pi from being burnt due to an external short circuit.
Two output modes, except for the regular output via USB port.
At high currents, such as for high loads above 2.5A, the voltage drop across the USB cable is a problem that cannot be ignored.
Therefore, we provide a 2.54mm header, which is welded at the Raspberry Pi GPIO 5V interface for direct power supply, to minimize the cable damaged and pressure drop.
This is only partly correct, and is generally bad advice.
The polyfuse actually only protects the Pi if power is supplied through the microUSB connector. It will then protect against 5V rail problems on the GPIO connections, through on-board shorts, and on the USB port of A models. The USB ports of B models are prtected separately, IIRC. Note that there is no polyfuse on Pi0 models. The most important protection is to reduce the possibility of fire should a fault occur, the protection of the board itself is somewhat limited since most electronic devices will blow far faster than the polyfuse. There are additional protection elements, notably a TVS, to help with incorrect supply problems (but see the note below about power applied via the GPIO header).
The polyfuse sets a limit of 2A5 for the current drawn ( actually peaks can be higher, since the trip characteristic is quite "soft"). This is for the board and all peripherals. This requires the use of thick and short supply cables -- for example, the "official" PSU uses 18AWG wires. Lower numbers are thicker. USB signal cables are often only rated for 500mA.
Applying the power to the GPIO power pins will do nothing in itself to reduce voltage drop, and will bypass the on-board polyfuse. If you must supply power this way, you should provide your own polyfuse or equivalent protection.