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I am trying to power about 20 Raspberry Pis at once using the GPIO pins. Each Pi has about 15W power requirement (3A @ 5V). So 20 Pis would have about a 300W power requirement. There are a few ways to go about this and I'd just like an opinion on which one is best.

One way would be to just get a 300W 5V power supply like this one and just connect them all directly. This would cost the least however I'm worried without a VRM the voltage might not be clean enough for the Pis, especially at max load. Is this a real concern?

Another way would be to get a 12V PSU and connect each PI with a cheap VRM like these (least cost-efficient), or a single large 300W VRM that every Pi connects to (more cost-efficient). I don't have much experience working with VRMs and only understand what they do at a high level. Would a single large VRM have the same issue as a 5V PSU in regards to the clean voltage required by the PIs?

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    \$\begingroup\$ This sounds like a shopping question, which would be off-topic. \$\endgroup\$ Commented Sep 2, 2021 at 14:36
  • \$\begingroup\$ Hi Gabe, if you try editing your question and rephrasing it to be more conceptual (How do I do X with Y limitations) instead of requesting shopping recommendations, you'll receive a better response. \$\endgroup\$
    – Bort
    Commented Sep 2, 2021 at 14:59
  • \$\begingroup\$ "I am trying to power about 20 Raspberry Pis at once using the GPIO pins." The Pi is not powered through the GPIO pins. What are you trying to do here? \$\endgroup\$
    – Transistor
    Commented Sep 3, 2021 at 9:58

3 Answers 3

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Central power is by far the lowest cost, and best performance, not counting distribution wire which is best done with twisted pairs of suitable gauge like CAT wire pairs ganged to 1 pair.

Add 3A PTC polyfuses for protection.

If they are not interconnected, then ground loops and additional Buck regulator noise are non-issues.

Noise immunity from antenna effects can be improved with large ferrite beads on V+ and low ESR or plastic caps at ends. But that depends on lightning and cable length if shielding is needed.

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You don't specify which model of Pi you will use, so I can't do it for you, but here's what you should do:

Look at the schematics, or the board itself if schematics are not available. Most likely what you will see from the power input is a a C-ferrite-C filter, then a PMIC chip or other type of switching converter to generate the voltages the various chips need (3V3 IO, cpu core, RAM, etc).

Most likely none of these chips use any 5V at all, which means the highest voltage on the board will be 3V3. Next, check the specs of the onboard PMIC chips to see what input voltage it likes. If its highest output is 3V3, it will probably run fine down to at least 4V. Allow some margin for wire and ferrite bead resistance.

So, the onboard switching PMIC chip is your VRM, you don't need another one. All you have to do is do a little bit of math to make sure voltage drop in wires won't be a problem.

You especially do not need the counterfeit "LM2596" module you listed. It, will not work for long, and when the output capacitor pops because it is a trash quality general purpose cap used way above its ripple rating, then output ripple will become so high that output voltage peaks rise about 5.5V, and your Pi's will all die from overvoltage.

Apart from that, the usual advice: a 5V 300W power supply will have enough output current to melt wires and connectors, so make sure you use one polyswitch or fuse per output, don't daisy chain, etc.

Since the boards most likely use standard USB connectors, you could simply make a power distribution board with 5V and GND planes, USB sockets, and one polyswitch per socket. Make sure you don't neck down the power/ground planes, since they pass a lot of current, use short USB cables with enough copper in them, etc.

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Buy a good quality power supply and don't overload it. If it has multiple output terminals for each voltage rail, use them; don't connect everything to one terminal.

"Star" wire the Raspberry Pis. Ideally run power leads straight back from each Pi to the power supply. If that isn't practical, use over-sized wires from the power supply to a set of positive and negative power rails, and connect each Pi back to those.

Definitely don't "daisy chain" the connections, looping the power lines from one Pi to the next.

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