Archived from groups: alt.comp.periphs.mainboard.asus (
More info?)
In article <41c4a0a4_3@mk-nntp-2.news.uk.tiscali.com>, "Jordan Petkov"
<jordan.petkov1@tiscali.co.uk> wrote:
> Can anyone tell me what is the better option:
> buying a new PSU that has 24 pin ATX power output or finding a 20 to 24 pin
> power converter?
>
> Price-wise the answer is clear, but how much could the converter affect the
> performance of the motherboard? Would this be a sensible solution? The PSU
> under consideration is an Antec True Power 430W. I have read good reviews
> about its reliability and I would like to stick with this one.
>
> Thank you in advance for your help!
>
> Cheers,
> Jordan
Have you downloaded the manual ?
Page 2-25 (=pg.51) has a section on power and what is an adequate PSU.
ftp://ftp.asus.com/pub/ASUS/mb/socket939/A8N-SLI%20Deluxe/e1889_a8n_sli_deluxe.zip
There is mention of EZPlug, and it is possible that if you use
EZPlug (a disk drive power plug), the 2x2 ATX12V connector, and
the 20 pin ATX connector, you'll be all right.
An FX-55 has a TDP of 104W.
http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/30430.pdf
That is 8.7amps. Assuming a Vcore converter efficiency of 90%,
the current drawn from the PSU becomes 9.6amps on the +12V. That
power comes through the ATX12V 2x2 power connector. The connector
pins have a rating of 2x8amps = 16 amps, which is enough for the 9.6.
To get representative graphics card current numbers, I use these:
http://www.xbitlabs.com/articles/video/display/ati-powercons.html
http://www.xbitlabs.com/articles/video/display/ati-vs-nv-power.html
This data is for the 6800 Ultra (AGP version), and the PCI-E card
would have the addition of the bridge chip.
http://www.xbitlabs.com/misc/picture/?src=/images/video/ati-vs-nv-power/6800u_table-b.gif&1=1
+5aux=3.89A +12aux=4.52A +3.3AGP=0.18A +5AGP=0.59A +12AGP=0.10A
Assuming the PCI-E version of the card doesn't have an Aux power
connector on it, all the above current would come through the
motherboard. That is 4.62amps per video card, time two for
SLI. That is 9.24amps. Add 1 amp for fan headers on the motherboard,
and you are at 10.24 amps.
If you use a 20pin ATX power connector, there is only one +12V
power pin. The 24pin ATX power connector would have two +12V
power pins. These pins are rated for 6 amps each. Let us assume you
use the ATX20 pin connector - so far we have 6 amps to work with.
Now, plug in the EZPlug. A disk drive connector pin is rated
for 8 amps. Now we have a total of 14 amps, to supply 10.24
amps of current (for an overclocked 6800U SLI pair). I think
that would still work. Without the EZPlug and using the
24pin ATX power connector, it looks like it would still work,
but with slightly less margin.
Now, let us look at the PSU. This hypothetical gaming system
draws a total of 9.6+10.24 for processor+2*video+fans. Call
that 20 amps, and that is without a couple amps for some
disk drives. The Antec 430W has 20 amps exactly on its
+12V output. To run the hypothetical system, you would be
advised to use the Truepower 550W, which has 24 amps on
+12V. (Note: When buying supplies this big, be aware that
some of them chop up the +12V output, into separate output
windings, and if you are not careful, one of the windings
can have too much load on it. Examine the datasheet for the
power supply carefully, to catch products with this bad
"feature". If you see +12V1=xx amps, +12V2=xx amps, that
means the supply has separate windings, and to use the
supply, you have to know which winding goes to which
connector.)
You should be able to adjust the above calculation for
your intended configuration. I doubt the +3.3 or the +5V
will present a problem.
This page gives some measured wall power for some SLI
configurations. The max is 330W, and that will require
some serious air volume through the computer case. Since
the power supply is typically 70 percent efficient, a
fair portion of that heat comes from the PSU itself.
330*0.30=99 watts inside the PSU worst case. Expect the
PSU to get hot (unless you can find a more efficient
high power supply).
http://www.anandtech.com/video/showdoc.aspx?i=2284&p=5
This web page has a formula for working out the number
of CFMs of air needed to cool your computer. See
"Chassis Temperature Rise From Installed Cards":
http://www.chassis-plans.com/cooling_and_noise.html
As to the performance question:
The Antec Truepower series uses feedback on all three
major outputs. If you look at the 20 pin ATX power
connector, you'll see two wires stuffed into a pin, on
three of the pins. The thinner of the two wires is a
sense wire. The voltage will be exactly 3.3, 5, and
12V, where the sense wire touches the pin. If you
use an extender cable, the power supply cannot compensate
for any voltage drop in the extender cable, so the voltage
on the motherboard might be a tiny bit lower. I would
not expect this to be a problem.
If you are planning on doing a high end SLI config,
buy a "510 Express" from here ($229). With 34 amps on
+12V, no worries about stability...
http://www.pcpowerandcooling.com/products/power_supplies/maxperformance/turbocools/index_hp_atx.htm
Have fun,
Paul
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