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I have two separate power feeds presented as either two IEC C13 or two UK 3 Pin sockets (the choice is mine).

I would like to connect my Pi to both power feeds so that if one power feed fails, the Pi remains up, how can I achieve this?

I guess there is a couple of things to consider here;

  1. As I have two separate power feeds I don't want to connect them together (I know that is kind of diving into electronics questioning tertiary).

  2. Is there any reason this wouldn't be supported by a Pi? I guess this depends on how I present the power feeds. Presumably if I used an ATS for example the Pi would be none-the-wiser. What about connecting both feeds to the Pi directly at the same time, is this possible?

  3. I think that connecting two power feeds to the Pi might not be feasible (in that is might kill the Pi or the Pi might allow both power feeds to become connected to each other damaging other equipment on those feeds). So, can I connect a feed and a backup battery to the Pi simultaneously? Perhaps in series with a rechargeable battery would work?

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If you connect the C13 / UK 3-pin sockets to two PSUs that each converts the 240 V AC into 5 V DC you can use suitable diodes to connect these 5V conductors to the RPi to ensure one power supply doesn't drive current into the other. Diodes have a voltage drop so you'd need to take that into account when selecting the PSUs. –  RedGrittyBrick Nov 29 '12 at 11:58
    
.. so they won't in fact be 5V PSU's. :) You can add a regulator after the diode, though, and you won't need adjustable or exactly right sized supplies. –  XTL Nov 30 '12 at 7:23
    
raspberrypi.stackexchange.com/questions/3697/… Related question and answer here. –  XTL Nov 30 '12 at 7:24

1 Answer 1

You should be OK if you use Schottky diodes. To quote the Wikipedia article on the same "A normal silicon diode has a voltage drop between 0.6–1.7 volts, while a Schottky diode voltage drop is between approximately 0.15–0.45 volts"

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