In article ,
Henri Derksen  wrote:

>Me is told to never draw more power from your Pi than 2 Amps at a Pi 2B,
>or not more then 2.5 Amps on a Pi 3B.
>If you connect a 5 Vdc= 6 Amp power supply to your Pi's input power socket,
>and you took more dan 2.5 Amps from it by GPIO or USB devices,
>you will blow the power input fuse from your Pi 3B's input power socket.
>So if you need more power then that the Pi can handle, buy an external powered
>USB2 hub, or power the GPIO externally with buffers (resistors),
>as others told here.
>So giving your Pi a higher Amperage feeding than it can handle is potentially
>dangeroues. I.e. feeding a Pi 2B with a 2.5 Amps Pi 3B power supply, or
feeding
>a Pi 3B with a 4, 5 or 6 Amps power supply.
>So keep it at max or below 2.5 Amps for the Pi 3B and max or below 2 Amps for
>all the other Pi's.
>You know each USB port may only take 0.5 Amps as a max.,
>but donot exceed the max. Amperage the Pi can handle, or your Pi will go down,
>i.e. stops running. That can crash the software on the SDcard.

Hm.

The Pi (or any electronic device) will only draw what it needs. You
could use a 5v, 1000 amp PSU on a Pi and it'll be fine.

The Pi v2 and v3 both have a 2.5 amp polyfuse (self resetting) on the
5v input.

Additionally the USB system has an overall current limit of 1.2 amps -
this is limited by a little bit of electronics (switchable from 0.6 amps
to 1.2 amps on the v2, but not switchable on the v3). You can pull 1.2
amps out of one USB socket or spread over all 4.

The 5v power output on the GPIO pin has no separate limiter (other than
the input polyfuse) and there it is possible to 'crowbar' the Pi and
cause it to powerdown/reboot if you short the 5v to 0v. The input fuse
is there to stop the PCB melting.

What you don't have much protection from is connecting the 5v signal
directly to a GPIO pin - then you have 5v going into a 3.3v system. If
the 3.3v pin is set to output then you can destroy the output driver
(and possibly other things too). You mostly get away with it if the pin
is set to input mode.

Gordon

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