In article , "Dragoncarer"
wrote:

Uhm...so I've connected my A8N-SLI up and everything, but the board has a
24-pin power connecter, my PSU has a 20-Pin connecter. I didn't realise all
this until I installed the Mobo because, well...I'd never hear it discussed
before. Is this going to be a problem? Currently it's running fine and I
haven't had any Mobo problems that could be attributed to the PSU.

Many thanks.

The 24 pin power connector is the same as the 20 pin connector,
except there are a few extra power signals on it. The reason
for this, is the PCI Express card slots can carry more power,
so the power connector was beefed up a bit.

The most crucial difference is the +12V situation. On the
20 pin power connector, there is only one wire carrying +12V. It
powers anything on the motherboard that needs +12V (except the
processor, and it uses the separate 2x2 power connector). If you
were using more than one PCI Express plugin card, and they
drew a lot of current, you could overload the single pin.
A pin on the 20 pin ATX power connector can safely carry 6 amps
without serious overheating, so that is the limit for one pin.

On the 24 pin connector, they added a second +12V pin, which means
the connector can carry up to 12 amps total current.

If the only PCI Express card being used is a single video card,
chances are the loading on the single pin is within the
6 amp limit, so there should be no harm. The A8N-SLI has
the EZ-Plug connector as well, and if you use that connector
in addition to the 20 pin power connector, that virtually guarantees
there won't be a problem. The EZ-Plug (disk drive) connectors
are rated at 8 amps carrying capacity, so using EZ-Plug plus
the 20 pin power connector makes room for 6+8=14 amps, which
is enough for two video cards.

There are two concepts at work here. One concept is the amount
of current the power supply has to offer (that limit is printed
on the label on the side of the power supply). The current has to
flow through some number of connector pins, and both the pins
and wires have current limits (if exceeded, the metal gets hot
and the plastic can melt). The numbers I've mentioned above,
are the safe operating limits for the pins on the 20 pin ATX
power connector, and for the disk drive connector plugged into
EZ-Plug. Using the EZ-Plug is a good form of insurance, and
can be used with one or two video cards (it is not restricted
to running two video cards).

Now, this topic is a bit more obscure, but I'll mention it
for the sake of completeness. This article mentions the
splitting of the +12V rails on some of the high end power
supplies.

http://www.madshrimps.be/?action=get...&articID=3 32

Older ATX power supplies have exactly one +12V circuit. Some
of the 500W+ power supplies can have +12V@34A or more as outputs.
There are no issues with using a supply like this, because all
+12V power comes from the same circuit. There is no wasted
capacity, as the 34A can be used by any load. (Splitting
the output means, if one output doesn't use all its juice,
the other output cannot gain access to it.)

On the newer 24 pin power supplies, there are two outputs -
12V1 (processor 2x2 connector) and 12V2 (everything else).
A supply like this is OK to use with EZ-Plug on your board,
because the 24 pin ATX power connector, and its two 12V wires,
run from 12V2, as do the disk drive connectors. Plugging in
the EZ-Plug won't harm anything in this case.

There are supplies that have three or four +12V regulator circuits
in the power supply. According to the madshrimps.be review above,
the power rails split like:

(Common Plane System) (Split Plane System)
12V1 Processors 12V1 Processor 1
12V2 Processor 2
12V2 Motherboard 12V3 Motherboard
12V3 Disk drive plugs 12V4 Disk drive plugs

I would be careful with supplies like this. If you plug in the
24 pin power plug, the two 12V wires run on a different 12V output
than the disk drive plugs. Plugging in the EZ-Plug in this case,
connects say, 12V2 to 12V3. If the power supply is not designed
for this, current will flow from one 12V circuit to the other,
which is not desirable. Note that the A8N-SLI is not listed
on the web page below, and I'm not sure if the reason is because
of this 12V issue or not. At the very least, if buying a supply
with three or more +12V output circuits, I would want to ask the
power supply maker whether using it on the A8N-SLI is a wise idea.
You cannot connect outputs on a supply together, unless there is
provision in the power supply design for current sharing.

http://www.pcpowercooling.com/produc...r/?show=T85SSI

The safest course of action, when shopping for a 24 pin power
supply, is to stick with the common 12V1/12V2 type supplies.
At the bottom of this web page, is a short list of "certified"
SLI power supplies, and I would find a supply with one or two
12V output circuits. The Turbocool 510 SLI has one 12V output,
and would be a reasonable solution. The Enermax EG701AX has two
12V outputs, and would also look to be safe as a choice. So
far, it looks like the Turbocool 850 is the only one I would
not want to use with an Asus EZ-Plug type motherboard. (And
at the price they are charging for the 850, I doubt anyone
will be buying it anyway. The design is still impressive, having
all that power, and only using a single cooling fan.) While
the EZ-Plug concept can improve the quality of power delivered
to the video cards, the same objective can be met by locating
the 24 pin power connector close to the video cards, and a
motherboard design without EZ-Plug won't have this issue with
shorting 12V2 to 12V3 etc.

http://www.slizone.com/object/slizone_build.html

HTH,
Paul