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I had a question that I was hoping someone could help with. I am building a cluster of raspberry pis to do research on and I decided the best way to power all the nodes was through micro usbs. (I figured if I did it through the 5v pins, then I would have to add fuse protection and design/implement a PCB board for 40 nodes - which will take quit a lot of time) I was in my lab and I found two left over power supply boxes from other projects. They are Thermaltake TR2 W0070 430W ATX12V v2.3 Power Supplies (here is a link to view the specs: http://www.newegg.com/Product/Product.aspx?Item=N82E16817153023). Is it possible to use this power supply to power the pis (using the micro usbs) or should I look for another option such as a 10 port AC adapter (e.g. like this one: http://www.meritline.com/10-ports-usb-20-hub-power-adapter-included-with-ac-adapter-white-with-silver---p-56107.aspx)? If it was possible, how would I do it?

Thank you very much for your help in advance, I really appreciate it!

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  • \$\begingroup\$ Why do you have to add fuse protection if powering it via the 5V pin? \$\endgroup\$ – Ignacio Vazquez-Abrams Sep 12 '14 at 2:38
  • \$\begingroup\$ With the raspberry pi B+ when using the 5V pin, it routes a protection that the micro usb enables. Technically it's not necessary per say, but highly recommended in case there was a power surge, failure, etc. that might cause a problem with power to one of the pis (and possible bust it). \$\endgroup\$ – Billy Thorton Sep 12 '14 at 2:53
  • \$\begingroup\$ The fuse is only really going to protect you from a Rpi that goes short circuit. Surges within the power supply will not blow the fuse until it damages ICs enough to cause a short circuit condition (after which you've probably broken all 40 RPi's). If one or more RPi draws too much current, the power supply will shutdown safely by a fuse which limits the overall current out. When squeezing out 28Amps, bear in mind you need some chunky cable to take that kind of load. \$\endgroup\$ – Oliver Sep 12 '14 at 9:17
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In short, yes. If you go to the Specifications tab you can get the output specs:

+3.3V@22A, +5V@30A, +12V1@18A, +12V2@17A, -12V@0.3A, +5VSB@3A

A single Raspberry Pi will theoretically draw 700mA at most, but generally peaks at around 500mA. (source) So, if you have 700mA (we may as well design for worst-case) drawn by 40 Raspberry Pis, you'll have a net current draw of 28 amps. This means you could use the 5V@30A rail from just one of the power supplies to power the entire cluster! However, you'll still need a way to split that power 40 ways, and if you want to add the fuses go ahead; if you can't find 750mA ones, 500mA slow-blow types should work (assuming you want one fuse per node). If you simply want a mains-side fuse (I wasn't sure based on your post-may as well cover all the bases), I think 1A (at 115V) would be sufficient.

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    \$\begingroup\$ When connecting so many devices to a single power supply, it would be smart to get USB cables with ferrite beads. They can be stripped and connected to a power supply via long terminal block \$\endgroup\$ – Volodymyr Smotesko Sep 12 '14 at 8:51
  • \$\begingroup\$ Very smart indeed, although board mounted (through-hole or SMD) beads are also available and might make the design a bit simpler, or self-contained. \$\endgroup\$ – RICK Sep 12 '14 at 16:13

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