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PSU Multi Rail usage explanation needed?..

Discussion in 'Hardware' started by trueno!, 31 Aug 2015.

  1. trueno!

    trueno! That's TRUE-N-NO if ure not sure!..

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    Hi,

    I have a question regarding multi rail designed PSUs...

    I have an Antec TruePower New 650w PSU that utilises a multiple of 4 rails +12v1/+12v2 ( 22A each ) & +12v3/+12v4 ( 25A each ) which all combined to 54A total maximum output limit...

    As you can see from my sig below I have an R9 280X graphics card which is connected to the non-modular PCI-E cable that consists of an 8pin ( 6+2 ) PCI-E connector with 6pin PCI-E connector extended off it and from what I can see/gather off the PSU this cable is linked up the +12v2 rail which only has 22A...

    So, with this in mind am I wrong to assume that the graphics card only has 22A to play with or is this cable able utilise the maximum amperage ( 54A ) spread across the 4 rails for this non-modular PCI-E cable and providing that this is the only 12v ( with the exception of HDDs & SSDs ) cable being used and no other 12v cable ( in relation to PCI-E ) is connected via the modular ports?..

    Just trying to understand why it states on the PSU connections that the +12v1 is for drives +12v2 is the non-modular PCI-E cable and +12v3/4 is for the other PCI-E modular connections when each +12v rail are all interconnected and not electrically separate, this is all very confusing to me, you know!..

    Any ways thanks for your time and thanks to you all that reply... :thumb:
     
  2. trig

    trig god's little mistake

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    Back in the day, these questions were right up my wheelhouse. Thanks mostly to the Guru, lol. Multi rail was mostly a marketing gimmick, as very few power supplies actually had separate trails, they were mostly just programmable and any single rail could pull the max amperage and watts rated. A quick google and it looks like your unit truly is. Most graphics cards companies will overvalue how much power and amperage their card actually takes, so I doubt you'll have issues. But if you want to be careful, I would use one of the included modular pci-e cables and then the other from the hard wired cables. Looks like ocp is rated to 40 amps, so that tells you something
     
  3. trueno!

    trueno! That's TRUE-N-NO if ure not sure!..

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    Hey trig,

    Much oblige with your time to reply this rather insignificant question!.. ;)

    Last night I had a quick play around in the menu system on Hearthstone and upon loading the game up it reached around 45A max and then settled down to around 25-35A...

    I will have to check the amperage while I have more time to play a more intensive game and see what I max out and settle down on...

    However it does seem that although the graphics card connected to the 12v2 rail, that PCI-E cable draws over its rated amp limit, which leads me to thinking that these rails are not true separate rails...

    Just as I've read around, they're just traces on the PSU PCB and the wires are efficiently wired up to each cable for ocp compatibility and combined max amperage when needed!..

    Though it still confuses me to why they label each connection as separate 12v rails even though they are really interconnected rails?..

    Any ways, think I'll stop thinking about this and go onto other things I have planned to sort out throughout these few weeks...

    :thumb:

    Sent from my SM-G900F using Tapatalk
     
  4. Deders

    Deders Modder

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    I used to own one of these, and one of my first threads on this forum was about load distribution on this PSU. From what I remember it is 1 single rail with over-current protection on each rail to stop everything going bang if something really bad happened. Whether it is or isn't a true multirail design isn't important as you will soon realise....

    Firstly rail 2 is purely for the CPU. If you tried to plug the 8 pin connector into you GPU it wouldn't fit and if you were really persistent and somehow succeeded, something would blow up.

    What you have to remember is that the motherboard will supply up to 75W to the graphics card via the PCIe slot. This will come from the same rail that supplies the rest of the motherboard and drives (rail 1)

    The amount that gets supplied through the slot varies for each card but you should allow for 75W when considering multi card setups. This is one of the reasons for SLI/Xfire certification as a PSU with only 18A on that rail just wouldn't cut it.

    The rest of the card will be powered from either of the 25A rails. You may as well just use the one cable as the load from this rail won't be that much. Probably about 12A on a visually demanding game like Metro last light. I always wondered why they didn't make the first rail the biggest. No graphic card is going to be able to make full use of 25A.
     
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  5. trueno!

    trueno! That's TRUE-N-NO if ure not sure!..

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    Thanks Deders!..

    That kinda makes more sense to me... 12v1 is for the PCI-E slots, peripherals, drives & whatnot, 12v2 is for the 8pin EPS, & 12v3/4 is for the PCI-E cables including the one PCI-E cable that is permanently attached to the PSU, which means that most of the 12v goes towards the 2 25A rails for the graphics cards when connected... How about the 24pin, does that use a combination of the 4 rails to distribute that cables juice?..

    Am I getting close to how this PSU is configured?..

    Any ways great to get a better understanding this... Cheers!.. :thumb:
     
  6. Deders

    Deders Modder

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    I'm pretty sure the 24 pin is from the 1st rail. The extra 4 pins came in when PCIe was introduced so that's where the slot power comes from. Obviously the non 12v wires will come from their respective rails.
     

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