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This is your standard EPS/ATX12V connector used for feeding the main processor VRM on a computer motherboard. The two 4pin connectors can be attached together to create an 8pin connector. The top four pins are +12V and the bottom four pins are ground.

EPS12V

I was recently taking a look inside one of my old power supplies and noticed how two of the +12V pins go to one 12V rail and the other two go to the second 12V rail. Then I see this webpage says the name of pins 7 & 8 are 12V2 (if the PSU has a second 12V rail.)

  • I thought it was a no-no to combine the two separate 12V rails together?
  • Does the EPS12V connector and main VRM keep them separate or is it no different than taking two wires from separate 12V rails and just tying them together for increased current capability?
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  • \$\begingroup\$ playtool.com/pages/psumultirail/multirails.html \$\endgroup\$ – Bruce Abbott Dec 5 '19 at 9:18
  • \$\begingroup\$ Thank you that was a good read. From what I know now, it must be that the main VRM on a computer motherboard keeps the two rails separated. \$\endgroup\$ – he65 Dec 8 '19 at 1:56
  • \$\begingroup\$ Should be easy to tell by measuring resistance between the sockets. I don't own a motherboard that needs such a ludicrous amount of power, so I can't verify. \$\endgroup\$ – Bruce Abbott Dec 8 '19 at 2:11
  • \$\begingroup\$ Easy enough to do real quick so I just went and poked an ohm meter into a motherboard I have laying around and the reading was near zero between all four of the +12V pins on the 4/8pin EPS socket. I made sure I was measuring the +12V side by first checking which side was ground by holding one probe of my DMM to a known grounding point on the motherboard (such as the shielding around the back I/O ports.) So, if I'm not mistaken, this tells us that the two +12V rails are being bonded together on the main VRM input. \$\endgroup\$ – he65 Dec 8 '19 at 2:19
  • \$\begingroup\$ That matches the observation my link, that standard ATX power supplies have their 12V outputs bonded together inside the PSU. \$\endgroup\$ – Bruce Abbott Dec 8 '19 at 2:26

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