Power up from USB Cable or GPIO?

Question

I have made a battery pack to power up my Raspberry Pi 3 for a project. The pack uses 2 Samsung ICR 18650 Li-Ion batteries (connected in series) and a 5V 3A UBEC and gives 5.05V output.

Now I'm a bit nervous trying to connect this to my RPi, the UBEC has a GPIO connector on the output end. Initially I just wanted to cut that off and replace it with a micro USB plug and just power up the Pi the conventional way, but then I thought that using GPIO to power up might not be a bad idea as well.

Honestly saying i don't want to fry my Pi just by powering it inappropriately. So which way do I choose, GPIO or microUSB?

Answer 1

Pet peeve - you can't power via GPIO, you power via power rail pins on the expansion header.

Feeding via the microUSB power socket is the safest option.

1. you get the protection of the polyfuse
2. you won't be able to plug it in the wrong way around

That said I have connected my UBEC output to a two pin female plug which I plug into pins 4 (5V) and 6 (ground) making sure it's the right way around before I switch on.

Answer 2

To repeat joan's point these are NOT GPIO connectors or GPIO plugs.

There is absolutely nothing wrong with powering the Pi via the power pins on the expansion header, provided you are sure the supply is safe i.e. 5±0.25V.

Strictly to follow the Foundation guidelines you should include protection similar to that on the Pi, which is to protect the Pi from overvoltage and transients. This should not be necessary for a UBEC.

A number of commercial products do power the Pi this way.

A UBEC should be perfectly safe, however you connect it.

My problem with the µUSB is the unavailability of µUSB connectors (at least in small quantities). The use of old cables has its own problems - not least being the inadequate size of the wire, which in many cases is difficult to solder.