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I need to power a cluster of 8 Raspberry Pis 4 and I have a 480W PC PSU with a maximum load of 28A on 5V+. My question is really simple and dumb (sorry for that) but I did not found a precise answer, but when I attach them to the 24pin motherboard connector should I use all the five 5V+ cables and 5 ground respectively? PSU cables are 20awg, and I estimated 3A for the Raspberry Pis so a total of 24A.

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  • \$\begingroup\$ Can you provide more detail. Are the RPis plugged into a single motherboard (if so what is the model/manufacturer, do they have any recommendations for connecting power? Is there a power bus on the motherboard or is each RPi plugged into power independently? Clearly you can't run 28A through a power cable rated for 3A for an individual RPi. What do you mean by 5V+? \$\endgroup\$ – mhaselup Sep 15 '20 at 3:01
  • \$\begingroup\$ There's no a motherboard, I have a PC PSU with the following maximum loads i.imgur.com/2rYMDrE.jpg and I want to power 8 Raspberry Pi 4 without having 8 adapters and to put everything in a PC case. So I am picking five 5V+ wires from the 24pin atx cable i.imgur.com/kF52Bv1.jpg and two from the two molex lines of the PSU, and also 8 GND wires from the 24pin atx cable and other two GND wires from the two molex lines. That's the maximum number of cables that I can pick from the PSU, so they should be able to carry 28A. \$\endgroup\$ – gabrielepmattia Sep 16 '20 at 5:58
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Yes, you should use all the 5V conductors and at least as many GND to reduce voltage drop over the cable; using extra grounds would only help. With 5 supply and 5 return wires, each conductor will be carrying almost 5A. Even this starts to push the limit of what you would want going over 20AWG.

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  • \$\begingroup\$ @gabrielepmattia If you will use this PSU only for RPi's cluster, you could open the PSU, disconnect (cut or unsolder) all the other cables, and even replace the bunch of 5V conductors with a single thick conductor. Or connect the RPi's USB-C cables directly to the PSUs PCB. \$\endgroup\$ – mguima Sep 11 '20 at 19:24
  • \$\begingroup\$ Yes, thank you for your remark you are clearly right but I wanted the PSU to be replaceable without any further soldering, so I am using a 24pin ATX extension cable i.imgur.com/Vs3WDwx.jpg to pick the five 5V+ wires, and 8 GND wires. The female can be easily attached to the PSU and the male to a simple switch like this i.imgur.com/CCEKI4B.jpg I also pick other two 5V+ and GND wires from the two MOLEX lines of the PSU, for a total of 7 5V+ wires and 10 GND wires \$\endgroup\$ – gabrielepmattia Sep 16 '20 at 5:49

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