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I'm trying to build a Raspberry Pi cluster (at least 32 Pi's) and I need a convenient way to power them all. So I'd like to design a power distribution board. The distribution board will have USB power ports for each Pi and it will be controlled by an Atmel microcontroller.

I currently have a 350W 5V supply, which can safely supply a hefty 60A. Assuming that each Pi will draw between 800mA and 1A, I should have more than enough power.

With that said, as a new engineer (who specializes in digital electronics), I've only designed one PCB before. I've never done anything with high power before. What design considerations should I take into account when designing the PCB?

I've done a little bit of research and everything seems to point to using a PCB bus bar to carry the high current. I would then branch off the bus to each individual Pi. The other option is to use a high power connector like this one. I'm kind of leaning towards the latter.

With that said I should also probably provide some level protection circuitry for the Pi's in case of a power surge (although my supply, a Cotek AK-350-05, should be able to provide a fair amount of protection itself). I was thinking of placing a 1.5A PTC in series with each USB port.

Are there any other things I should consider? Thanks

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  • \$\begingroup\$ Depending on which type of Raspberry Pi you are going to use, you might need to account for higher maximum A's per Pi. I'm easily able to power "normal" B and B+ Pi's from a 1.5A rated power supply, but had to switch to a 2.2A rated powersupply for my rPi 2 B+'s. So your 800mA-1A range might not be sufficient, and you might need to count on 1.5A-2A per Pi (at least during startup and processing peaks). \$\endgroup\$ – Phil B. Apr 23 '15 at 11:20
  • \$\begingroup\$ Hmm, that could be an issue. I'm using R Pi 2's \$\endgroup\$ – audiFanatic Apr 24 '15 at 16:16
  • \$\begingroup\$ Note that my findings are WITH a usb keyboard/mouse combo and an Edimax WiFi dongle plugged in, as well as a monitor. If you plan to run this setup as an ethernet-only, no USB devices computing cluster the max Amps might be much different. I'd do some measurements on a single Pi just to figure out what you're dealing with. \$\endgroup\$ – Phil B. Apr 24 '15 at 16:19
  • \$\begingroup\$ Yea, I'm only gonna be using ethernet and ssh. The USB ports will not be used \$\endgroup\$ – audiFanatic Apr 24 '15 at 16:25
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Consider also a distributed approach with point-of-load (POL) converters. The idea is that you distribute power across the board at lower current and higher voltage. Presently, you are thinking about having one AD/DC converter which outputs 5V 32A which goes directly to RPis. You could have an AC/DC which outputs 48V 3.5A. Each RPi has a dedicated DC-DC buck converter (the POL converter), which generates 5V 1A from 48V. This way, you are only dealing with more manageable 3.5A and 1A currents on your board.

enter image description here
(Source of the diagram.)

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I've worked on PCB-based bus bars before (over 1kW total power) and we were able to get by with just a PCB, no external bus bars.

Here are some of the things to consider:

  • Copper thickness: use 2oz / 70um (or greater) copper for your PCB.
  • Add solder islands to further increase current carrying capability. [1] [2]
  • Calculate the temperature rise and add forced cooling if necessary.

Here's a quick example calculation using the Saturn PCB Toolkit:

Conductor Properties

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