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Thread: dual 12v rails on new psu's.. info please..

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    dual 12v rails on new psu's.. info please..

    Hi guys..

    Was wondering, I've noticed that all v.2 ATX psu's and above sport dual 12v rails. My questions on this are:

    1: How is a psu with a single 28A 12v rail different from a psu with dual 14A 12v rails?
    2: Does "dual rails" mean that there are two leads instead of one? Is that standard compatible with any SocketA motherboard? Does it mean that I can only use one of the 2 rails if my motherboard is not brand-spanking new (and supports that feature) ? I currently have the Abit AN7.

    Cheers!

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    My Tagan 2Force 530Watt operates as either a split rail or combined rail PSU.

    What you have, basically, is 12V power delivery to the motherboard (usually the CPU power circuitry, I think) on a separate rail from within the PSU to that which you hook all your other device up to. So you have two 12V rails, independant of each other. Load on one shouldn't affect the other. The reason they do this and don't just whack loads of output on one rail is because of the ATX PSU specification which says you need to add a second rail if current demand will exceed 18 amps.
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    Thanks for the reply Steve!

    Now, to recap, you're basically saying that -from the outside- the psu looks the same, it's just the inside that's different?
    Meaning, there's still *one* connector for the motherboard, but that's fed from a different source (rail 1) than the molex's, sata's and fdd's (rail 2)?

    If that's the case, it means that, as far as the consumer is concerned, nothing has changed... We still connect the psu the same way as before, same cables, same everything. The dual rail thing is just something that has changed to make the PSU's more reliable under heavy load, right?

    Thanks in advance!

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    You'll see the +12V (the four pin) power connector that goes to the motherboard will have a slightly patterned yellow cabling on it (providing the PSU maker bothered to use the right cable) to signify that it's coming from a different rail.

    In theory, with a split PSU you could be a bit lacking for 12V to your devices, regardless of how much juice the CPU/mobo is using, but that doesn't seem to ring true, in reality.

    But yes, the PSUs essentially look the same, but electrically they're different to meet new standards and the requirements of new components, particularly motherboards.
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    Same connectivity, better reliability.
    I'll go for a v2.00 then.

    Cheers Steve!

    I'm torn between almost the whole line of Tagan (quite a few @ 420-430W available at Scan), Akasa PaxPower2-3 (at Savastore), Antec SmartPower 450 + NeoPower 480 (at Ebuyer). Tough choice! Any suggestions?

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    Well my Tagan hasn't missed a beat.

    What spec is your system?
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    Steve, I got an Athlon XP-Mobile 2500 @ 3200, Abit AN7 mobo, 2*512 PC3200 ram, 2 IDE drives using raid0 (via a PCI ide raid card), 1 SATA drive, 1 dvd recorder, 1 dvd rom, 6 case fans, 1 floppy, 1 Thermaltake volcano hsf, 2 uv tubes, 1 Soundblaster Audigy, 1 fan controller (no lcd, just knobs) and I use 1 usb gamepad and 1 usb webcam. Keyboard and mouse are PS/2. I don't think I'll upgrade my system any further, maybe a new gfx card in a year or so (I got a Radeon 9550 at the moment) but that's it.

    What do you think? Will 420-430 Watt cut it? I reckon so, but your opinion will be appreciated I originally had a budget of £40 (GBP), but I suppose I can stretch it to £50-55.
    Last edited by mounaki; 16-09-2005 at 06:01 PM. Reason: forgot some information

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    If your motherboard is a bit old, check to see if you require a 20-pin or a 24-pin ATX power connector. I think most (if not all) new ATX v2.0 PSUs come with 24-pin connectors. I'm not sure if these will work on your board without a 24->20 pin adapter, so check before you buy.


    BTW, the Tagan 380W should suit you: http://www.scan.co.uk/Products/Produ...oductID=138557

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    Quote Originally Posted by Rohan
    If your motherboard is a bit old, check to see if you require a 20-pin or a 24-pin ATX power connector. I think most (if not all) new ATX v2.0 PSUs come with 24-pin connectors. I'm not sure if these will work on your board without a 24->20 pin adapter, so check before you buy.
    You can usually fit them with the extra four pins just hanging off and not connected as the rest of the pinout is the same. Tagans have a detachable 20/24pin ATX connector anyway, or at least some of them do.
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    Ah OK, I didn't know that. He's probably best off going for a good ATX v2.0 PSU then, because it'll be more future proof and he can use it in his next system.

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    Thanks for all the replies guys, much appreciated. Buying my new PSU first thing on monday. Cheers!

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