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Single rail vs multi rail - want to make sure I understand this.

Hello,
I have looked over forums and read some information on the power supply single vs multi rail and I believe I understand it, but just want to make sure I am correct. I know I don’t have all the terms right – just making sure I have the overall idea.

You have two 850W power supplies. One has a single +12v rail with 70A. The PCI Express connector is 6 x 6+2 pin.

Second Power supply is multi rail. +12V is 2@22 and 2@25. PCI Express connector is 2 X 6 pin and 2 X 6+2 pin.

GPU requires min 42 Amps and has one 8 pin connector and one 6 pin connector.
Both power supplies will work, correct?

As I understand, the multi rail is basically a single rail but spread out for “safety”. Because it has the correct PCI Express connectors, there is no issue. As I understand, the issue would come in if you had to use an adapter to get the correct PCI express connector, which could over end up overloading the rail. Is this correct?

I also understand you don’t just add up all the rails to determine the amount of amps.

Thanks,
3 answers Last reply Best Answer
More about single rail multi rail make understand
  1. Best answer
    It seems like you got it.

    This power supply review might make you understand a bit more (the reviewer puts it in terms we can all understand, without oversimplifying things):
    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=216
    The first page of the review is most pertinent. :)
  2. Labtec600 said:
    Hello,
    I have looked over forums and read some information on the power supply single vs multi rail and I believe I understand it, but just want to make sure I am correct. I know I don’t have all the terms right – just making sure I have the overall idea.

    You have two 850W power supplies. One has a single +12v rail with 70A. The PCI Express connector is 6 x 6+2 pin.

    Second Power supply is multi rail. +12V is 2@22 and 2@25. PCI Express connector is 2 X 6 pin and 2 X 6+2 pin.

    GPU requires min 42 Amps and has one 8 pin connector and one 6 pin connector.
    Both power supplies will work, correct?

    As I understand, the multi rail is basically a single rail but spread out for “safety”. Because it has the correct PCI Express connectors, there is no issue. As I understand, the issue would come in if you had to use an adapter to get the correct PCI express connector, which could over end up overloading the rail. Is this correct?

    I also understand you don’t just add up all the rails to determine the amount of amps.

    Thanks,


    Hi - actually you answered all the questions yourself. All the things you
    understand are correct. However, some of the best PSU's out there use
    single rail (if the PSU is well built & designed), and are very safe at the
    same time.

    Yes, for PSU's with multi +12v rails you need to refer to the PSU's documentation
    for the tot +12v amps avail. Or if it's a mainstream brand, you can find that info
    here:
    http://www.realhardtechx.com/index_archivos/Page541.htm

    Yes, both the PSU's you referenced above would work with the
    +12v - 42a required GPU, with lots of headroom. Meaning in this example
    an 850w unit is overkill (unless planning on SLI or CF)

    Also, in a multi +12v rail setup, as long as your CPU & GPU are different
    rails, then if you had to use an adapter, you'd be OK on either rail.
  3. Alright - thank you - just picked best based on first response.
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