I have a question about multi rail +12V capacity on a Gigabyte Superb E720 PSU with 4x +12V rails each with an 18A capacity. The Gigabyte PSU has 2x 6+2 Pin PCI- E 2.0 connectors and 4x 4-pin Molex connectors. Each +12V rails is listed with a Cable Color: +12V1 is Yellow/Blue, +12V2 is Yellow/White, +12V3 is Yellow and +12V4 is Yellow/Black. How is the 18A per rail distributed across the connectors? Each 2x 6+2 Pin PCI- E 2.0 connector can supply 18A? How about the other 2x 18A rails? Do they supply power thru the 4 Molex connectors? how? Thanks.
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There's not that much difference between single rail and multi rail PSUs. The whole current carrying capacity of the multi rail PSU is available even w/o all the +12V cables being connected. It basically boils down to what it will take to shut down the PSU as it gets loaded up. On a multi rail PSU, if one rail's current exceeds the rating for that printed circuit board 'trace', it will shut down the PSU. On a single rail PSU, there is no Over Current Protection (OCP) per trace; the current would have to exceed the single rail rating to shut down the PSU. Both PSUs still provide the same amount of power as needed.
See this for a better explanation: http://www.overclock.net/t/761202/single-rail-vs-multi-...
Thank u for the prompt reply clutchc. I read the link for Single Rail vs. Multi Rail *Explained* and I understand the OCP limit which in the case of my Gigabyte Superb E720 PSU would be 18A on any one of the connectors. I am still confused about the individual connector Watt capacity, specifically the 6+2 Pin PCI- E 2.0 connectors and 4-pin Molex connectors. If I have a GPU that requires 2x 6+2 Pin (or 1x 6+2 Pin and 1x 6 Pin), does that mean that my Gigabyte Superb E720 PSU can only deliver 18Ax12Vx2=432Watts? Also, if I use a 2x Mollex to 1x 6+2 Pin adapter and I connect 2x Molexes (from 2 different cables coming out of the PSU), does that mean now that this new 2x Mollex to 1x 6+2 Pin can deliver 18Ax12Vx2=432Watts and one of the other existing 6+2 Pin can deliver 18Ax12V=216Watts for a total power delivery to the GPU of 432Watts + 216Watts = 648 Watts. Thanks.
The individual connector wattage capacity is usually somewhat less than (18A * 12V) * 4. The total +12V system wattage is usually listed on the nameplate listed somewhere. How the individual cables are wired as to the 4 rails is anybody's guess. You'd need a schematic of the PSU to find out.