ASUS A8N32-SLI Deluxe ATX - power supply question.

Discussion in 'Asus' started by Philly, Nov 12, 2005.

  1. Philly

    Philly Guest

    Is the ASUS A8N32-SLI Deluxe ATX compatible with a non-EPS12V power
    supply? Specifically, I have a brand new Antec SmartPower 2.0 500W PSU
    that I would like to use in any new system I might build.

    I was considering getting the new DFI LANParty UT nForce4 SLI-DR
    Expert motherboard until I read this:

    "EPS Power Supply Units are Required for DFI LANPARTY NF4 SLI-DR
    Expert and DFI LANPARTY UT RDX200 CF-DR motherboards."

    I'm concerned that the new ASUS A8N32-SLI Deluxe and the new Abit AN8
    32X (due out November 30) might have similar restrictions on PSU.

    Philly, Nov 12, 2005
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  2. Philly

    Paul Guest

    The DFI LANParty UT nForce4 SLI-DR Expert is here:

    It has a 2x4 12V connector and a 24 pin main power connector.
    The 2x4 is black in color and is next to the 24 pin.

    They must be expecting a pretty hefty AMD processor, to need
    four wires to carry +12V. AFAIK, the fastest X2 draws 110 watts,
    and at 90% efficiency for the Vcore converter, that amounts
    to 10 amps, which should have been easily handled by a 2x2 12V
    connector (the two 12V pins on that connector are good for at
    least 6 amps a piece, and 2*6 is greater than 10).

    Pg.68 - "If available, it is preferable to use the 8-pin power;
    otherwise connect the 4-pin power connector..."

    The DFI uses a floppy disk drive (FDD) connector, to perform the
    same function as the Asus EZPlug (molex) connector. That connector
    is supposed to add room for extra amps to flow to the two video
    cards +12V. I doubt a floppy connector pin has that high a current
    rating, but I suppose every bit helps.

    A video card slot has five 12V pins nearest the faceplate. At
    one amp a pin, a max of five amps should flow in there. Based on
    the measurements that Xbitlabs has done in the past, the most
    current drawn through those pins is in the vicinity of 4 amps.
    (If more current was required, the video card maker would use
    a separate power cable instead, and all the 12V would be coming
    through that. In that case, they could have 8 amps if they wanted,
    if not more.)

    With two video cards, that is 2x4 = 8 amps. The only other load on
    the motherboard is the three fan headers, and if we toss in 1 amp
    for that, the total motherboard load is 9 amps.

    If you use a 20 pin ATX power connector, that gives room for 6 amps
    of current. With one video card and your fans, a 20 pin connector
    will handle the load by itself.

    If you use a 24 pin connector, that gives you two 12V wires, for
    a total ampacity of 12 amps for the 9 amp load.

    If you further use the Asus EZPlug, the ampacity would increase by
    another 8 amps.

    On the Asus board, you could use a 20 pin power connector, and
    the EZPlug molex connector, to have an ampacity of 6+8=14 amps,
    which is again greater than the 9 amps of two SLI cards (or
    the theoretical max of 11 amps, with two 5 amp video cards plus

    To summarize the 12V motherboard loading situation (ignoring the
    separate processor power connector, as it was already described
    at the beginning of the posting):

    Load - 1 video card plus fans = 1 x 4 + 1 = 5 amps from 12V
    2 video cards plus fans = 2 x 4 + 1 = 9 amps from 12V
    Theoretical max 2 x 5 + 1 = 11 amps from 12V
    (separate video power cable used if more is needed)

    Ampacity - ability of wires to carry current and not get so hot
    as to melt the wires or oxidize the connector pins

    20 pin connector 6 amps (via the one pin)
    20 pin connector + EZPlug molex 6 + 8 = 14
    20 pin connector + DFI FDD 6 + ??? (maybe total 10 amps?)
    24 pin connector 12 amps (via two pins)
    24 pin connector + EZPlug molex 12 + 8 = 20
    24 pin connector + DFI FDD 12 + ??? (maybe total 16 amps?)

    I don't know the rating of an FDD connector, so the above ???
    is just a guess on my part.

    The other aspect of supplying amps of current, is location. It
    is more worthwhile on at least one Asus board I looked at, to
    connect the EZPlug, as it is right next to the video cards.
    The close proximity reduces voltage drop to the load, which can
    be a stabilizing influence.

    While what DFI has done for the processor is generous (extra pins
    leave plenty of room for the current), the presence of a 2x4
    connector is bound to scare a few customers off. I think the
    A8N32-SLI uses a 2x2 connector for the processor, so no issue

    One other issue to mention, in terms of power supplies, is bigger
    is not always better. There are several monster ATX supplies,
    like the PCP&C Turbocool 850, that instead of having dual
    12V outputs (12V1 and 12V2), they have four outputs. The problem
    with this, is if a motherboard uses an "EZPlug" or an FDD drive
    connector to gain additional power for video cards, this
    actually connects two of the 12V outputs together - which is
    verboten. Unless specifically designed to handle that situation,
    loop currents can flow, destabilizing the supply. If you want
    to buy a "universal" supply, able to handle just about anything,
    I would recommend a supply with 12V1/12V2 output only, for max
    compatibility. If, on the other hand, you are a "PSU hacker",
    it is always possible to rewire the outputs, such that this
    problem won't happen. In any case, if buying a triple or
    quadruple 12V output power supply, make sure you get a detailed
    wiring diagram, so you know which rail is on which connector.
    I find lately, the companies making these monster supplies,
    are getting pretty sloppy in their documentation, so beware.

    Paul, Nov 12, 2005
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  3. Philly

    John Lewis Guest

    Hogwash.... they are just trying to push their new power-supplies.
    The A8N32-SLI has the usual square 4-pin 12V (ATX12V1 ?) connector
    for the CPU core power, plus a 24-pin ATX connector. You can use a
    20-24pin adapter for this latter connector, if necessary.

    John Lewis
    - Technology early-birds are flying guinea-pigs.
    John Lewis, Nov 12, 2005
  4. Philly

    John Lewis Guest

    Agreed, stay away from these monsters.

    For a desktop system using an AMD processor up to X2 4800+,
    such as the DFI Lanparty SLI or the A8N32-SLI, even with a pair of
    7800GTX, there is no need for one of these ridiculous power-supplies
    - what with the weight and the poor efficiency at light load. A bit
    like buying a Hummer H1 - an outlandishly expensive, inefficient
    status symbol. Something like the Enermax EG565AX-VEFMA 2.0
    or the EG701AX-VESFMA2.0 is just fine and dandy, plus they come
    with ALL required power-connectors including SATA, in ample quantity.

    John Lewis
    - Technology early-birds are flying guinea-pigs.
    John Lewis, Nov 12, 2005
  5. Philly

    Philly Guest

    Thanks John Lewis and Paul for the replies. It's good to learn that
    the Asus A8N32-SLI has 24 and 4 pin power connectors and not 24 and 8
    pin (EPS12V) like the DFI LANParty UT nForce4 SLI-DR Expert.

    Paul points out that the DFI Expert manual indicates that a non-EPS12V
    power supply can be used. That's good to know, but when I asked at
    DFI-Street (the DFI forum) I was told outright that I'd need an EPS12V
    power supply, that my Antec SmartPower 2.0 500W PSU isn't good enough.
    Maybe it's hogwash, but that plus some reported problems with the
    "Expert" means I'll probably steer away from it.

    The Asus A8N32-SLI, on the other hand, is flying out the doors at
    e-retailers. The biggest complaint seems to be that they keep running
    out of them, and it's extremely hard to get. That's good for Asus, bad
    for people like me who have a dead mobo and can't afford to wait for
    next year's Socket M2s.

    Philly, Nov 16, 2005
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