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I have a Raspberry SC15184 Pi 4 server and I'm looking to power 3 USB peripherals each with a 3-6W power requirement (which should be 0.6-1.2A given pi-4 operates at ~5V).

This is above the 1.2A restriction for pi-4 so I would need a powered USB hub. However, I stumbled upon this article -- about poorly made powered USB hub could have backfeed that could cause pi-4 to be stuck on reboot. I'm trying to make the pi-4 into a server so this is obviously a big issue.

Unfortunately, the recommended USB hub in the article above may not be able to handle the power requirements of my USB peripherals (3 x 3-6W each, ~18W max). Does anyone have a good recommendation of powered USB hub for my case? Or know where I can look? This backfeed issue seems to be never advertised and only discussed on raspberry pi forums.

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  • Is using multiple powered hubs an option?
    – Mast
    Apr 3, 2022 at 14:13

4 Answers 4

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This is strictly not backfeeding, as you need to first boot the Pi from another power source, but still annoying.

Backfeeding was a problem with the Pi Model B (which had a very basic power circuit).

I solved my backfeeding problem by making an adapter with a Shottky diode in the 5V line, allowing the Pi USB to power peripherals but preventing backfeeding. You could just cut the 5V line if you always use a powered hub.

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  • Thanks for the response. 2 follow up questions: 1) Could you explain what you meant by "strictly not backfeeding but still annoying"? I am planning on powering the pi-4 with a real power usbc power supply. But I'm not sure if a poorly chosen powered USB hub would cause server reliability issues once I leave it running. 2) I think I have the model B (amazon.com/dp/B07TC2BK1X/ref=dp_iou_view_item?ie=UTF8&th=1). What do you recommend that I should do? (I'm not sure what you meant by the 5V line, sorry I'm new at this).
    – Discombobulous
    Apr 3, 2022 at 0:39
  • You do NOT have a Pi Model B (which was released 29th Feb 2012 and is no longer made). USB has 4 wires, 2 data, Gnd & 5V. Other issues are opinion based - the above is not strictly a reply to your Question (which is off topic) but meant as a helpful suggestion to avoid the problem.
    – Milliways
    Apr 3, 2022 at 0:51
  • See raspberrypi.stackexchange.com/questions/11820/…
    – Milliways
    Apr 3, 2022 at 0:54
  • Ahh, I see what you mean now. Backfeeding is only an issue if the main power source of Pi comes from the USB hub itself. Whereas in my case, the main power source is elsewhere and I'm only using the powered usb hub to support additional peripherals. Thanks.
    – Discombobulous
    Apr 3, 2022 at 1:10
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This is a known problem on the Creality Ender3 printer, where a Pi will continue to power the control board via USB when mains power is switched off.

The solution is to modify a USB cable such that the 5V line has a short section removed. This wire is mostly coloured RED but YMMV.

  • Carefully cut a short section of outer jacket, using an I shaped incision.
  • Snip out the shielding such that you can see the red wire.
  • Nip out 5~10mm of red wire
  • Optionally insulate the ends so they can't short on the ground foil OR cut back the foil so it can't short.
  • Re-lay the outer plastic sheathe and wrap in tape or heatshrink.

Essentially this is a USB Vasectomy, in that all the other wires work but the power wire doesn't connect through to your USB hub. And that USB hub must receive power from a wall supply for this to function.

I'd suggest doing this on the cable to your USB hub (if it is separate) or use a short extension cord between Pi and Hub that has had this snip.

You can sometimes do a low-effort version by placing a small piece of electrical tape inside the USB connector, but this is fiddly and liable to fail after a while. Not recommended.

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  • Just to clarify -- If both of my pi-4 and my USB hub are powered separately. (I'm only using the powered USB hub for data, connecting my USB peripherals to my pi-4) I won't be running into backfeed issues right?
    – Discombobulous
    Apr 3, 2022 at 21:44
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I read many posts about it and tried several tips. The best way remains to interrupt the 5V wire (VBUS) leading to the Raspi. Since I don't want to cut the cable of the hub, I stripped the 5V contact on the USB connector. To do this, I either take insulating tape and glue off the contact or I use nail polish, which I apply to the contact with a brush. Now there are no more problems with booting! For the pin assignment of the plugs see: https://www.aggsoft.com/usb-pinout-cable/usb3.htm

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I Used RPLidar powered through USB hub on my PI4, and never had a problem with backfeeding. The brand was belkin, this one

Belkin F5U404CWBLK 4 ports USB 2.0 hub

Funny thing is i was powering the hub via USB OUTPUT port through USB A to USB micro B cable, while USB micro B was the power source, not the usual 5v DC jack on the USB hub itself.

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