8 pin ATX 12V plug

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Hi all, Just picked up a new motherboard (Gigabyte MA785GM-US2H) for a
low power system. I'm coupling it up with the Athlon 64 2000+ 8 Watt cpu,
so obviously only single core. I hadn't intended on upgrading the PSU
just yet but my current supply only has the 4 pin 12V connector (in
addition to the 24pin obviously). Now i've read that the 8 pin is
required for multiple cores so seeing as I'll be using a single core cpu
is itb fine just to use the 4pins or do I risk damage in some way? Thanks

Re: 8 pin ATX 12V plug

Keiron wrote:
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Motherboards with a 2x4 power connector, may come with a 2x2 cap,
covering four of the holes. That is intended to show you, where to plug
a 2x2 connector, if that is the kind of supply you've got.

In terms of ampacity, I recommend to people as a rule, that
each yellow wire can support 6 amps. 6 amps is the figure for
a MiniFit Jr. pin and wire, on the main power supply connector.
When a MiniFit connector has a smaller number of pins, there is a
bit more cooling available around it, and less heat buildup. The
pins in that case, can be rated for slightly more current. If
a heavier wire gauge is used, that bumps up the current one
level as well.

Rather than waste a lot of time, dwelling on details, it's simpler
to just tell you to stick with a 6 amp limit. That is a conservative

OK, so now we can do power analysis for the 2x2 connector.

The 2x2 connector has two yellow wires. It can carry at most, 2x6 amps
or 12 amps. 12 amps times 12 volts is 144 watts input power to the
Vcore regulator circuit on the motherboard. The Vcore switching
regulator, converts that power to a lower voltage. The converter
might be 90% efficient. Therefore, I multiply by 0.90 and get
144 * 0.9 = 129.6 watts, or rounding, about 130W of power available
at the actual processor power pins.

And that means, it is safe to connect a 130W processor, using
only a 2x2 power connector.

You should also check the CPU support chart, before sticking a 140W
processor in the motherboard. Some VCore circuits don't support 140W
processors. A motherboard could come with a 2x4 connector and a 95W
Vcore circuit, for example. That would be lunacy, but for marketing
reasons, the 2x4 connector may be used to fool people into thinking
it is a "powerful" motherboard.

OK, using this chart as an example, you can't even stick a 140W
processor in that motherboard. The highest power processor is a 125W.
The only way those extra pins on the connector would come in handy, is
if you were doing an overclock of that 125W processor. At stock
speeds, the 125W processor would be adequately handled by a 2x2 connector.


I have heard of some cases recently, where there were malfunctions unless
a 2x4 connector was used on certain motherboards. I haven't heard of an
explanation yet, as to why that was necessary. Presumably, there is an
issue with the motherboard design, but we can't go running around
claiming "the sky is falling", when it clearly isn't. If you're using
less than 130W of power, a 2x2 should be sufficient.

My motherboard has a 2x4 connector and I'm using a 2x2 connector. So
I'm not exactly in a state of panic :-)

Another thing to note about 2x4 connectors, is there is more than
one wiring pattern for them. So don't grab just any supply, and attempt
to use the 2x4 connector on it, without verifying it is the right type.

For example, this article describes pinout of ATX GES type, which
is quite different. And likely, a hard to find power supply.


This article has more information about "regular" ATX wiring. If
the ATX12V 2x4 connector has four identical yellow wires and
four identical black wires, sitting in separate rows, chances are
it is intended for your motherboard.



Re: 8 pin ATX 12V plug

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The 4 pin should continue to work just fine. Although I haven't come up
personally with an 8 pin cpu power power connector I've read many reviews of
purchasers on newegg.com using their old PS 4 pin connector on a new mb with
an 8 pin connector and it working. The only thing I've read though is the
additional 4 pins are supposed to support a more robust graphics display
card rather than the additional cpu cores as you mentioned.
   You may want to check the manual of the mb to see what it says.
Additionally, scroll down and read what 'NA' had to say in reference to the
question you are asking about your mb...

Jan Alter

Re: 8 pin ATX 12V plug

On 10/08/2010 11:25 AM, Jan Alter wrote:
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The last machine I put together worked fine with the four pin PSU (in
the 8 pin mobo)

One word of caution: It's actually possible to mix up the additional 4
pin connector with the *other* 4 pin connector typically used on P-IV
mobos. They are not interchangeable...but the manufacturers stupidly
made the keying all the same. I'm sure someone , somewhere has blown
something up!

Re: 8 pin ATX 12V plug

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In the end, they sell more motherboards and PSUs.  It's only
stupidity from the point of view of defective customers, who
obviously can't tell the difference between identical looking 4
pin connectors.  This sounds like something Dogbert would say.

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