Confused Regarding EPS 12V Power Supplies

[Gilbo]

What I think I know:
1. A lot of higher end non-server motherboards these days require a 24-pin ATX connector. EPS 12V power supplies have these connectors.

2. These motherboards also require a 4-pin 12V connector. EPS 12V power supplies have an 8-pin, not a 4-pin 12V power connector, which server motherboards use.

So what exactly am I supposed to plug in to these new 24-pin ATX motherboards? Do EPS12V power supplies have a 4-pin 12V connector and an 8-pin connector? Are there non-EPS motherboards with 24-pin ATX connectors and 4-pin 12V connectors, and no 8-pin 12V connectors. Je suis confus...

 

[Gilbo]

Oh, I also think I know that you can plug a 20-pin ATX power supply into a 24-pin ATX connector motherboard and nothing will explode, but the opposite is not a good idea.

However, I figure, if I'm buying a new power supply, I may as well buy the right kind.

 

[Gilbo]

Okay, I think I might be able to answer my own question. I keep seeing ATX 2.0 around, and I looked up the specification and it specifies a 24-pin ATX connector.

Strangely, it seems the specification does away with the 4-pin AUX connector, which I still see on many new motherboards with 24-pin ATX connectors. So I'm still partly confused. New question:
1. Does this mean if you plug in a 24-pin ATX2.0 power supply that you aren't supposed to also use the 4-pin connector? IE, the 4-pin connector on the motherboard is a compatibility thing, so the it is only connected to the PSU if you're running an older 20-pin power supply?

If you can't tell, I'm apparently a little out of date on power supply technology.

 

[Fushigi]

I have absolutely no idea for sure but it sounds like they just integrated the 4 pin connector into the 20, making it 24.

 

[Gilbo]

I just looked at the manual for the board, a DFI NF4 Ultra-D, that should be arriving in the next couple days and it definitely says that the 24-pin and 4-pin connectors should both be used. Oddly enough, however, it specifies that power supplies that feature such connectors are "ATX12V Power Supply Design Guide Version 1.1."

As far as I know, it's ATX 2.0 power supplies that have 24-pin connectors.

I'm going to do some more research.

 

[Gilbo]

According to page 27 this document the ATX12V 1.1 standard specifies a 20-pin connector. So I assume the manual contains a typo.

Looking up the ATX 2.0 Power supply spec on the same site indicates that ATX 2.0 Power supplies do indeed retain the 4-pin connector, despite what I read in an article google turned up at Tomshardware that declared the connector had been removed in the new spec. I know Tomshardware turns out crap, but come on. They didn't even bother to look up the spec for their article...

Sorry for all the posts . I should have researched longer before posting. It was pretty easy to find out. I'd even been to formfactor.org before...

 

[sechs]

If I recall correctly, through version 2.03, the ATX standard specified a 20-pin mainboard connector. Intel created a new standard, called ATX12V which added the 4-pin connector to power the processor.

The SSI standard people appear to have been specifying a 24-pin mainboard connector for some time. As much as I can tell, the 24-pin connector is exactly like the old 20-pin plus Intel's 4-pin connector.

At some later point, the SSI folks realised that they were going to need a lot more 12V to run Intel's increasingly power-hungry processors in dual and quad systems. So they specified an 8-pin connector that appears to only carry 12V and ground. They also began specifying multiple 12V rails. This is what we now call EPS.

Meanwhile, the ATX people were not standing still. The latest version of the standard (2.3?) specifies that 24-pin connector which the SSI people have had for some time. I guess that it also includes support for the 8-pin connector and PCI-E graphics connectors. I believe that it drops support for 4-pin connectors and -3.3V.

As I understand it, Intel is attempting to morph the ATX power supply standard into the BTX standard.

 

[Gilbo]

ATX12V 2.01 looks like what I need according to page 34 of this document.

Sechs, you brought out some useful distinctions. For example I hadn't realized that ATX12V x.y was different than ATX x.y. I am beginning to understand what is going on now thanks to your post. Thank you for making the effort to clarify things.

So, ATX12V 2.01 has the 4-pin connector which I need from its ATX12V heritage, which is dropped in the latest revision of ATX (no 12V), as well it has added the 24-pin connector, which I also need, and which has been part of the SSI standard for some time and has just been added to the ATX 2.3(?) spec, but was not part of the original ATX12V standard. LOL...

 

[mangyDOG]

Strangely, it seems the specification does away with the 4-pin AUX connector

I believe the connector you are referring to is not the new 4 pin square connector used on virtually all new motherboards but the one that looks like one half of an AT motherboard pair. This is great, I cannot remember ever using this connector and it has always been a pain to cable tie neatly out of the way.

The new 24pin motherboard sockets can be used with old 20 pin ATX power supplies with out any issues. Just ensure that the power supply you use is able to supply the required power on the +12v rail. The new high end motherboards (SLI etc) the require a lot of power (recommendations run from 17 to 25amp depending on number of PCI-e cards and other items) I have several 400watt power-supplies which only have 15 or 16amp on the +12volt rail, and I have seen customers with (blown-up) cheapo "400 watt " power-supplies which only have 12amp on the +12v rail!!

cheers,
mangyDOG

 

[Bung]

So, ATX12V 2.01 has the 4-pin connector which I need from its ATX12V heritage, which is dropped in the latest revision of ATX (no 12V), as well it has added the 24-pin connector

ATX12V 2.2 has both 24 pin and 12V connector.

If you have a MB that uses the 12V to feed the CPU regulator and the main power connector for the rest of the 12V load, the 20 pin version only has 1x12V pin good for 6-8Amps??? The 24 pin connector adds 1 each of 12,3.3,5 and common.