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Goal: I wish to power 3 Raspi. I am currently running 3 USB C wires powering the device, but I wish to build or find ways to power them all using GPIO header power pins.

Background: Mechanical engineering student who is learning electrical engineering via online circuits and books

Constraints: 3 Raspis 5V/~2.5A

Current Readings: Since all uses 5V power, I understand that I require a 5V regulator and RPI max currents sum up to 7.5 amps, or let's say 8 amps. And since I am trying to use GPIO pins, which don't have overcurrent protection, I should design one as well(?)

Qs

  1. Would It be ok to power all of them using 5V 8A switch mode regulator in parallel?
  2. Would I require over-current protection? What would be a workable circuit? Do I need them in all three?
  3. What would be the initial source? AC-> DC -> DC5V ? or DC24V -> 5V? Would it be better to buy 5V 8A power jack adapter? and plug directly to the Raspis?
  4. If the Pis are in an Idle state, what happens to the currents?
  5. What more protection would I require?

Outro I read through many electronic engineering books, but I could not find a good solution to this situation. I would really appreciate it if you could even shine any light on this matter. Thank you.

Edits +a I was under weather after the cold. Sorry for not responding sooner. I understand that you can power RPi through one of the Power lines in GPIOs, which bypasses the internal voltage regulator. This method is similar to those PoE hats, or any other powering hats. (@SamGibson is right.) The main goal was to save some money on the type C plug and try to power through a self-built board.

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    \$\begingroup\$ I don't understand the question. Do you want to use GPIOs from a Pi or other microcontroller to control the power supply of the Pis and turn them on and off? \$\endgroup\$
    – bobflux
    Jan 7, 2022 at 8:50
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    \$\begingroup\$ Your question title sounds as though you hope to supply the 2.5 A for each Pi from a GPIO pin. GPIO pins can only supply 10 to 40 mA typically. Can you edit to clarify? I think you want to control the Pi's from GPIO. This doesn't sound like a good idea to me as you could shutdown during write to SD card, etc., and corrupt the file system. A better way would be to do an orderly shutdown by remote command over Ethernet. \$\endgroup\$
    – Transistor
    Jan 7, 2022 at 8:52
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    \$\begingroup\$ @Transistor - Hi, Agreed that the OP could clarify. Just FYI an unfortunate, but common, "shorthand" term with RPi users saying to "power it using GPIO" actually means to power their RPi using the 5 V (and Gnd) pins on the GPIO expansion header connector. So people referring to "powering their Rpi using GPIO" don't really mean they use the actual GPIO pins, but they actually use the adjacent power supply pins on the same connector as the GPIO pins. Here's a random article using (and explaining) that unfortunate shorthand. HTH. \$\endgroup\$
    – SamGibson ♦
    Jan 7, 2022 at 12:00
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    \$\begingroup\$ @SamGibson, thanks for the clarification. As to what should be done: use the term GPIO header. If an ambiguous term has sprung up in a spin-off community of electronics, here Raspberry Pi, then mainstream electronics should not mindlessly follow and adopt a term that throws away essential detail. Instead, the correct term should be used to introduce and educate that community on something they weren't aware of. Searches will work fine. Have modified question title accordingly. \$\endgroup\$
    – TonyM
    Jan 7, 2022 at 12:33
  • \$\begingroup\$ Please draw a schematic of what you are proposing. \$\endgroup\$
    – winny
    Jan 7, 2022 at 12:39

2 Answers 2

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The 5V pins on the GPIO header are connected directly to the USB C power connector. There's a voltage regulator on board that provides lower voltages for the Pi circuitry. As far as I know, the device doesn't use 5V directly however it is sent to the USB ports, so don't forget to include anything plugged into those ports in your total power calculation.

Unfortunately, the Raspberry Pi Foundation does not specify tolerances for the 5V supply; the spec sheet just says "5V." However, I have used these to power multiple Pi's without issue. You can use inline fuses between the power brick and the devices if you want, but they likely will not protect the Raspberry Pi's if, for example, you accidentally draw too much current from the GPIO pins.

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A device will draw the power it wants. Just because it has current availability, doesn't mean it will want it.

Use a 8 amp buck converter with CC and CV control. These have protection. But fuse the pin to your amp limit.

XL4016

Now if you buy a 5v shelf product, you may find you can get voltage sag, or brown out, so it's worth checking the loads and voltage. You can add a small cap to each to compensate for V sag. But it should be fine.

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