Re: A8N-SLI Premium PSU and EZ_PLUG Questions

In article <44B7C9C2.2040302@xxxxxxxxxx>, Barry Watzman
<WatzmanNOSPAM@xxxxxxxxxx> wrote:

The adapter (20 to 24 pin) will probably work, but getting a new power
supply would be a better approach. There's a large variability here in
terms of both power supplies and the actual current requirements of
different CPUs, so it's hard to be too specific.

The EZ plug is an alternative to the 4-pin square ATX12V connector for
getting power to the switching power supply on the motherboard that
supplies the CPU Vcore voltage. I've seen advice not to use both of
them, only use one or the other (use the ATX12V if you have it). With
single rail power supplies, it shouldn't matter, but if you have a
split-rail power supply, then using both the ATX12V and the EZ-Plug
might cause a problem by tieing the two rails together (the intent of a
split rail supply is that one rail is for the CPU Vcore and the other
rail is for drives and fans, and that they should remain independent).


You are thinking historically :-) There was a time when an EZPLug
was provided, when P4 processors first came out, and it was
for the CPU. The purpose of the EZPlug has cnanged since then.
It now bolsters the motherboard power distribution, for add-in slots.

EZPlug works in parallel with the main ATX connector. The processor
will not run, without its 2x2 connector.

ATX12V 2x2 square -------------------> CPU_Vcore_Circuit
power connector

ATX_main_power -----------+----------> Video card slot power
20 or 24 pin | Fan header power
|
EZPlug -------------------+

Not shown in the above diagram, is the difference between what
happens when using a 20 pin or 24 pin connector. The 24 pin
connector adds a few extra pins to allow more amperes to be
carried on the main DC rails. In particular, there is an
extra 12V pin. The 20 pin connector has one 12V pin. The
24 pin connector has two 12V pins. The 24 pin connector
in a way, does the same type of job, that the EZplug is
doing - making more room in terms of copper wires, for current
to flow.

For the current, there are several issues. There is the ability of
the power supply, to provide current. That is stated on the label
on the side of the supply. It might say 12V @ 20A. But to safely
carry all that current to the motherboard, requires enough pins
and wires to carry the current. And finally, something on the
motherboard has to draw the current, so all these precautions
are only needed for a high end hardware configuration.

In terms of "room" for current to flow, here are some possible
combinations of connectors.

20 pin ATX = 6 amps via one 12V pin
24 pin ATX = 12 amps via two 12V pins
20 pin ATX + EZPlug = 14 amps via 6A pin on main, 8A pin on EZPlug
24 pin ATX + EZPlug = 20 amps via 2x6A on main, 8A on EZPlug

An example of a slightly demanding video card combo, is two
6600GT video cards in SLI. They each draw four amps from their
video card slot, for a total of 8 amps. To run them safely,
you can use any connector combo offering more than 8A capacity.
(The 6600GT is the worst, because all the current comes from
the video card slot. There is not aux power on the end of the
card.)

If you installed two 7800GTX cards, they draw 6 amps each. But
the difference on these cards, is that the current is draw via
two places. Some current comes from the video card slot. Some
current comes from the power connector on the end of the card.
A breakdown of how much current flows in each, is not usually
available. And since the PCI Express connector standard has a
5A limit on the video card slot, my belief is that most SLI
pairs of cards will not be drawing more than 10A total via
the motherboard connectors in the table above.

The split between the two current draws on a video card with
aux connector, is explained in this article. See in particular
the explanation on page 6, which includes a chart.

http://www.xbitlabs.com/articles/other/display/fsp-vga-power_2.html

For best stability, I recommend plugging the main ATX and the
EZPlug, if you are using two video cards. With one video card,
I don't see a reason to use more than just the 20 pin, but
if you have an extra disk drive power cable, might as well
connect it.

As for the concept of the 20 pin to 24 pin adapter, that is
self-defeating. On the end of the adapter that plugs to the
power supply (the 20 pin end), all the current being drawn
flows through the single 12V pin on the connector. While the
24 pin end of the adapter is now running cool and comfortable,
the 20 pin end of the adapter gets just as hot. More hot in
fact, since the motherboard PCB and copper is not present, to
dissipate some of the heat. The only advantage of using such
an adapter, is transferring the point of failure, to the power
supply connector and the end of the adapter. At least the
motherboard doesn't end up with a burned connector.

And there is no need to burn any connectors, as long as you
are using the EZPlug to assist with the load.

HTH,
Paul
.

Relevant Pages

  • Re: psu requirements-think i found it
    ... :: jump from 20 pin to 24 pin? ... Ian, you can use a 20 pin power supply, on a 24 pin connector motherboard. ... and even less of an issue for the 12V rail. ...
    (alt.comp.periphs.mainboard.asus)
  • Re: Time to upgrade
    ... Intel Pentium III 501 MHz processor and 512 MB of RAM. ... You'll need a new power supply. ... The main power connector has 24 pins (and is compatible with ... For a video card, the new standard is PCI Express. ...
    (alt.comp.periphs.mainboard.asus)
  • Re: A8N-SLI & EATX
    ... > The 24 pin power connector is the same as the 20 pin connector, ... > except there are a few extra power signals on it. ... The EZ-Plug connectors ...
    (alt.comp.periphs.mainboard.asus)
  • Re: PSU versions
    ... Recently I replace with new power supply, ... notice the -5V pin is no more there. ... > 3) Changed connector to 24 pins, ... That basically means one video card plus ...
    (alt.comp.periphs.mainboard.asus)
  • Re: Possible Power Issue on Asus P5N-E SLI
    ... on the power draw of the P5N-E SLI. ... no more than 4.5 amps would be drawn from a video card ... A 20 pin connector can safely carry 12V1 ... which rail used is unknown - includes RAM ...
    (alt.comp.periphs.mainboard.asus)
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