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I am trying to create an in-car (headrest) entertainment system using the Pi 3B with 7" screen using OSMC, when OSMC is shutdown it does not fully power off the screen, I can detect the shutdown using one of the GPIO pins, so far so good, the problem arises when I boot using a 5A 5V supply (this is a 12v to 5v DC to DC converter) via the micro USB port, it acts like the micro USB cable I have is throttling the current although it is supposed to be a 2A cable, when I plug in the official RPi power supply it boots up as expected. I have tried multiple different DC to DC converters because I thought it may have been those causing the restriction but that's not the case.

From what I have read the options for powering the Pi and 7" screen

  1. Micro USB (best option with protection)
  2. Std USB port (not ideal and has its own problems and a 0.5A restriction)
  3. GPIO pins (again not ideal due to circumventing protection and current limit)

My question is how do I get the required current into the micro USB if all the cables i am finding throttle the required current? I suppose I can always cut the cable off an official power supply as that has a large current capacity but that seems a bit destructive, has anyone else come across this problem? Soldering directly to the pins is a bit tricky?

Any feedback appreciated Regards Simon

1 Answer 1

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Two options:

  • buy a cable. Look into cables for phones which support fast charge at 5V. Check the AWG rating printed on the cable: try getting something with AWG 22 or less. Pick one which is as short as required, not longer.

  • build a cable. Get a DIY USB cable connector and pick a couple of wires for 5V and GND. I've made such a cable for a Pi 4 using AWG 18 (that's 0.82 mm2 of copper, scavenged from a printer power cord) which is a bit stiff and tricky to solder, but works fine with a 4A power supply. Buying AWG 18 USB cables is almost impossible, but getting AWG 18 wires is no problem, and if you have old power supplies from printers / laptops, you may already have what you need.

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