How to supply redundant power to a Raspberry Pi from two PC usb ports?

Question

I would like to add a Raspberry Pi to an existing two-node server setup to get an utility / playing / monitoring linux system independent from the two PCs, but I can not actually consume another mains plug.

My idea would be to power the Raspberry Pi from USB ports of both PCs so if one goes down or gets shut down the Pi will always be powered, but I know / presume I should not directly connect the power lines of the two USB ports together.

This is possibly related to this other question but I have to interface to two actual PC usb ports and not two mains power supplies: I guess I don't have the luxury to afford voltage drops from diodes.

Getting someone to do some soldering work is not a problem, as far as I tell him exactly what I need :)

Is there any ready-made product or some schematic I could use to achieve this "redundant R-Pi power supply from two USB ports" ?

Answer 1

Use two schottky diodes, something like this:

Answer 2

https://www.8086.net/ sell dual feed-in usb power devices. Dual Ideal Diode devices which accept 2x USB Power in and then can power a raspberry Pi. If 1 of the power-in fails the other takes the full load.

They sell 3 versions:

• Bare USB-C out version with dual USB-C in: https://www.8086.net/products#80860019
• Basic USB-A version with dual micro-usb in:https://www.8086.net/products#80860012
• Raspberry PI hat with dual USB-C in: https://www.tindie.com/products/8086net/usb-c-dual-supply-splitter-5v/

Answer 3

I believe that there are in fact several products that do this. You can use the Startech Dual USB - micro USB Cable, or this OWC cable. It should be able to work, but I have not tested it personally.

If you have any issues, please contact me through the comments.

Answer 4

Maybe it's too straightforward, but can you just use a relay, for example a SPDT (Single Pole Double Throw) one? You may attach those two USB 5V sources to the two inputs of the SPDT relay and use the relay output to power the Pi. Also use one of the USB 5V to control the relay coil. Depending on the switching speed, you need to choose a certain size capacitor to keep the voltage from dropping too low during the switching.