24 pin ATX power vs 20 pin

Discussion in 'Asus' started by Jim, Mar 16, 2005.

  1. Jim

    Jim Guest

    I just ordered an Asus A8N-E motherboard that has a 24 pin power connector.

    I would like to use an Antec Truepower 550 power supply but it has a 20 pin
    power connector.

    Does anyone know if this board work with this power supply? Or do I need a
    20 to 24 pin adapter?

    (I don't want to spend the money on a new 24 pin power supply)


    Jim, Mar 16, 2005
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  2. Jim

    KC Computers Guest

    The 20-pin connector will work fine with that board
    without an adapter. It's not recommended if you
    will be using a high powered performance video
    card, however.
    KC Computers, Mar 16, 2005
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  3. Jim

    Jim Guest

    Kevin, thanks for the prompt answer to my question. When you say "high
    powered performance video," would this include the Abit Radeon X600 XT 128MB
    DDR PCI Express video card? My Antec 550 PS specification states that the
    12V supply is capable of 24 amps. Do you think this would be adequate for
    this card?

    Thanks again,

    Jim, Mar 16, 2005
  4. Jim

    Paul Guest

    And that is due to the 20 pin connector having only one +12V
    pin, while the 24 pin connector has two +12V pins. A single
    pin is rated for 6 amps, before it gets hot and potentially
    melts the plastic around the pin. A high end video card could
    draw 4.5A, and your fan headers draws a bit too. And depending on
    whatever else Asus loads onto the +12V, there could be a slight
    contribution as well. (Xbitlabs has articles, where they measure
    video card current consumption, so you can sometimes find
    numbers there.)

    If you use some kind of adapter product, that converts a
    20 pin to 24 pin, that really wouldn't help, as where the
    20 pin connector plugs into the 20 to 24 pin adapter, the
    same 6 amp limit would exist. (That means, there is still
    a potential to melt the plastic, but on the power supply end of
    the power chain.) If, on the other hand, the adapter consisted
    of a disk drive connector plus a 20 pin ATX connector on the
    source side, and a 24 pin connector on the destinaton side, then
    both ends of the adapter have two +12V pins, and then nothing
    can get damaged. (But I haven't seen any adapters designed
    that way.)

    old 20 pin cable 24 pin mobo
    x (pin not fed)
    PSU ----------------------------------x this pin fed
    Potential hot spot will be here ---+
    if more than 6 amps flows into mobo

    20 pin to 24 pin adapter
    +------------------x 24 pin mobo
    PSU --- 20 pin ------------+------------------x two 12V pins
    +--- Potential hot spot will be here as
    all current flows through one pin

    If I was designing an adapter, I'd want to combine a 4 pin
    disk drive connector plus a 20 pin power on the left, to
    feed a 24 pin power connector on the mobo on the right. I
    haven't seen one for sale like this.

    PSU --- 4 pin DD conn --+
    +---+------------------x 24 pin mobo
    PSU --- 20 pin -------------+------------------x two 12V pins


    Pin Signal Pin Signal
    1 +3.3 VDC Orange 13 +3.3 VDC Orange
    2 +3.3 VDC Orange 14 -12 VDC Blue
    3 COM Black 15 COM Black
    4 +5 VDC Red 16 PS_ON Green
    5 COM Black 17 COM Black
    6 +5 VDC Red 18 COM Black
    7 COM Black 19 COM Black
    8 PWR OK Gray 20 -5 V
    9 5 VSB Purple 21 +5 VDC Red
    10 +12V2 Yellow 22 +5 VDC Red
    11 +12V2 Yellow 23 +5 VDC Red
    12 +3.3 VDC Orange 24 COM Black

    Pins 11,12,23,24 are the extra pins added to the 24 pin
    connector, over and above the 20 pin connector. Pin 1 on
    both connectors lines up. To make an adapter, a source
    of a single +12V, a +5V pin, a +3.3V pin and a ground
    return pin are needed. A disk drive connector can give
    +12V, +5V, GND. The old style 1x6 Aux power connector
    could be used to donate +3.3V. Only the +12V is immediately
    critical, followed by the ground pin on pin 24. The +3.3 and
    +5V likely have enough current already.

    You could craft a good adapter, by taking a 20 pin to 24 pin
    adapter, and a disk drive Y connector. That should give enough
    materials to make an adapter that has two +12V pins on
    the left, to feed the two +12V pins on the 24 pin connector.

    Before spending the time on a project like that, it is best to
    chase down the power consumption numbers for your video card
    and for the fans fed off the same +12V supply. If the video card
    happened to have a separate power connector, so much the better,
    as that would really reduce the risk to the mobo power connector.

    Is this likely to be a problem ? My guess would be not
    too likely, unless the video card is really sensitive to
    the quality of the +12V. (So, maybe it won't burn, but maybe
    the voltage on the video card could be on the low side.) Asus
    put an Ezplug on the A8N-SLI and I really like that concept,
    as it would remove the risk entirely when using a 20 pin power

    Something else I noticed, when reading the manual (and this
    is for you dudes who buy stuff without reading the manual
    first) - while the A8N-E mobo has a PCI-E x4 connector on
    it, the tech writers use weasel words when they say
    "1GB/sec _total bandwidth_". How I interpret that, is
    512MB/sec up and 512MB/sec down, which means the slot only
    has x2 wiring placed on an x4 connector.(Note that the weasels
    couldn't just says "its a x2 slot - get over it".) Just in case
    you have a x4 disk controller board that expects a full x4
    rate, or that you care about such things.

    I wondered about that connector when I first saw the board
    specs, because it seemed like too much bandwidth for the
    typical bus bridges used on desktop chipsets.

    A sweet alternative, would be to use an SLI board, stick a
    video card in one slot, in x8 mode, plus a disk controller
    card in the second video slot (x8 mode, but only uses
    x4 mode bandwidth). But I still haven't read whether there
    are any restrictions on video slots being usable for
    generic PCI-E plugin cards, so i don't know if this is a
    viable option or not. It should work, but Nvidia controls
    the chipset drivers...

    Paul, Mar 16, 2005
  5. Jim

    Weaver Guest

    On Wed, 16 Mar 2005 08:09:00 -0500, (Paul) wrote:

    <snipped absolutely excellent info>

    Thanks Paul!

    Maybe you can clear up a mystery for mein that case :)

    I was using an Antec Truepower 550W p/s to power an Asus AN8 SLI mobo
    with a couple of 6800 cards

    After plugging everything in I still had need for one more Molex
    connection on the mobo, to be sure that enough power was getting to
    the SLI cards

    I was using supplied converters from Molex to 6-pin PCIX (videocard
    power sockets)

    I had no plug left after hard drives connected and so on so I plugged
    one of the hard drive power plugs that was part of a couple lashed
    together to power two hard drives - bit of a stretch. When I plugged
    it in there was the smell of doom :) and I replaced both the p/s
    (Noisetaker ATA2.0 600W) and mobo. No converters :)

    All the power plugs were inserted correctly so I'm left speculating
    that the EZ-Power (or similar name) socket on the mobo caused a short
    somewhere - but maybe you can explain it?

    Just wondering mate, everything's running fine and dandy now
    Weaver, Mar 17, 2005
  6. Jim

    Paul Guest

    Is it possible the converter was wired wrong ?

    It could either be a power supply failure, or a wiring error has
    resulted in an output being shorted. To figure out what happened,
    would require a multimeter. You would need to switch on the
    power supply (by connecting PS_ON# to an adjacent COM pin), and
    then verifying the voltages on all the connectors. Next, you would
    examine the converter wiring, to make sure the pins are in the
    right holes. You could even plug the converter into the PSU, and
    then measure the voltages at the end of the converter.

    If you have ever worked making wire assemblies, you would realize
    how error prone the work is. As a young engineer, I was annoyed to
    find one day, that our local shop had assembled some cables wrong.
    So, I decided to sit down and make sixteen of them myself. I was
    being very careful (because being a smartass, I was out to prove
    that they weren't that hard to make), and I managed to get one
    of them wrong. From that day onward, I had a fresh respect for the
    people who did the work, and all the correct ones they managed to
    make :)

    Paul, Mar 18, 2005
  7. Jim

    Weaver Guest

    Horses for courses yep. Like those guys who make the fishing flies :)

    Thanks again mate

    I should have realised when the power converter plugs only fitted
    loosely that something was going to happen - old engineer here and if
    something bad can happen it usually does doesn't it :)
    Weaver, Mar 21, 2005
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