Why is a pin missing on 2x12 PSU cables?

I just noticed that finally entry model PSUs are now giving 2x12 power leads rather than needing to use a 2x10 in addition to a snap on 2x2.

For the first time I actually looked at one and I thought I had a broken one, or one with a weird/wrong connection... It looked like a pin was missing in the middle and two cables going in to a single socket on the left most (what would be part of the 2x2 extension).

Anyway... I tried to Google this, and couldn't find any information, but, when I did a picture search, I saw the same thing... so, I can only guess it is meant to be this way!

enter image description here

Anyone know why this is like this?

William Hilsum

Posted 2014-11-11T11:36:55.777

Reputation: 111 572

Two cables going into one pin is probably Vsense – that is, the power supply senses the 12V voltage at the connector, closer to the load, and regulates it according to that. – ntoskrnl – 2014-11-11T12:35:55.447

Answers

There are two versions of the ATX power supply connector.

Version 1, was a 20 pin connector (2x10), and Version 2 is a 24 pin connector (2x12): ATX Power connector pinouts .

The -5V pin is no longer present on the version 2 connector, but otherwise pins remain in the same relative location (although numbered differently for pins 11 upwards). For backward compatibility, some power supplies carried on with a V1 connector, with an additional jumper for V2 compatibility. It is probably a commercial decision to remove that backward compatibility, as demand will have waned.

Rowland Shaw

Posted 2014-11-11T11:36:55.777

Reputation: 3 607

These pictures are a lot better/clearer than the pinouts.ru ones. Source? – Journeyman Geek – 2014-11-11T11:47:51.780

I feel so out of the loop recently, can't keep up with tech! Cool, that answers that one! I have a version 2! I just assumed it was the same old connector with the 2x2 permanently attached, I had no idea it was actually different. – William Hilsum – 2014-11-11T11:48:31.170

@JourneymanGeek I got it from here but I can't be sure if they originated it

– Rowland Shaw – 2014-11-11T12:56:56.580

This answer is wrong. As @J... mentioned it has nothing to do with 24-pin versus 20-pin. The last paragraph is nonsense as well; a 24-pin power connector that is split is not a "V1 connector" and the other 4 pins aren't a "jumper". It also completely ignores the sole purpose of -5VDC--the ISA bus. – Jason – 2014-11-12T16:52:17.727

The -5V pin was actually removed from requirement even on the old 20-pin connectors in ATX12V version 1.2 way back in 2002, although it was not prohibited by the specification. Guidance for the pin was phased out over the next few revisions.

Per the ATX12V 1.3 Specification

Section 1.2.1 Key Changes for ATX12V Version 1.3 :

-5V removal: Guidance for –5V has been removed. This legacy voltage was in support of ISA add-in cards. ISA cards are no longer used for a majority of the industry, but custom applications my still exist, refer to Version 1.2 for –5V recommendations.

J...

Posted 2014-11-11T11:36:55.777

Reputation: 686

I am no ATX genius, but a Google search revealed the same thing being discussed in several forums. It is the Pin-20 that is missing, which earlier was used to provide -5 volt supply. It is not present in most recent PSUs, as it is no longer used! So, your new PSU is pretty much safe to use! :)

jjk_charles

Posted 2014-11-11T11:36:55.777

Reputation: 1 087

+1 Thanks, but giving the mark to the most detailed answer. – William Hilsum – 2014-11-11T11:54:01.493

I myself prefer @Rowland's answer! – jjk_charles – 2014-11-11T11:55:29.347