Philly said:
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.
http://www.antec.com/us/productDetails.php?ProdID=26500
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."
http://www.nintek.com.au/x/scripts/nin_news_story.asp?NewsID=78
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
The DFI LANParty UT nForce4 SLI-DR Expert is here:
http://us.dfi.com.tw/Upload/Product_Picture/expert1.jpg
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).
http://us.dfi.com.tw/Upload/Manual/87900530.pdf
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
fans).
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
there.
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
