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I want to use the +5 VSB of a Seasonic PSU for powering a Raspberry PI 3. The PSU can deliver up to 3 A. I plan to grab it from the PSU side by crimping a split adapter for the 10-pin plug.

The PSU is the PRIME FANLESS PX-450, wired as follows:enter image description here

In my case, +5 VSB will be pin 9 (10P-9). However, I don't know which ground would be the best to use. There are three grounds available (pin 1, 2, 3) but I want to use the ground which is already used for +5 VSB to not overload something.

Is there anything other important for me to be aware of?

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  • \$\begingroup\$ Seasonic makes many kinds of power supplies. We don't know what power supply you have and which ground pin is best for +5VSB return. At least give a model number or link to data sheet. Is that a PC power supply? \$\endgroup\$
    – Justme
    Feb 4 at 12:53
  • \$\begingroup\$ Thanks a lot! Yes, it is a PC power supply. I edited my post and added the layout. \$\endgroup\$
    – Tintenfisch
    Feb 4 at 15:00
  • \$\begingroup\$ Check the current rating of the 5Vsb rail. The RP3 requires 2A, not all ATX PSUs can supply that on the 5Vsb \$\endgroup\$
    – Lior Bilia
    Feb 4 at 17:54
  • \$\begingroup\$ Definitely. This Seasonic PSU happily supports up to 3 A on +5 VSB. \$\endgroup\$
    – Tintenfisch
    Feb 4 at 17:57

1 Answer 1

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All ground wires on the power supply are connected together inside the PSU and other PC components. So, you are free to choose which ground connection to use. It might be better to connect all grounds together on your (receiving) end as well, but it won't make much difference either way.

The reason for having multiple ground wires is to increase the current capability. Each connection (+3.3V, +5V, +5VSB, +12V, -12V) needs a return path to ground.

Please also note that all ground wires are connected to the metal case of your PC and PSU, as well as to the earth ground on the wall plug.

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  • \$\begingroup\$ a) But let's say +12V already draws much current from ground no. 1. Isn't there a risk to overload the ground cable/the terminal if I then add +5VSB to it? Or is it so that already the +3.3V, +5V, +5VSB, +12V, -12V are connected to all grounds anyway from mainboard side? b) Makes it sense to ground the RPI to the case or is this considered as bad practise? I wonder if there exists a use case where someone would do that. \$\endgroup\$
    – Tintenfisch
    Feb 4 at 17:23
  • \$\begingroup\$ Yes, all grounds are connected together on the motherboard side. This goes for hard drives and other PC components too. If the 10-pin connector is shared with some other device or you have some other connectors on the same cable (example: bitprostore.com/wp-content/uploads/2020/05/…), then the best solution would be to connect all grounds together and connect your Pi to that connection. The case is grounded for EMI and safety reasons, so connecting to it is not common practice. \$\endgroup\$
    – Anton
    Feb 4 at 18:12

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