6 pin vs 6 + 2 pin PCI-E connector

[DoubleHelix747]

I bought OCZ StealthXStream OCZ600SXS 600W ATX12V / EPS12V SLI Ready Active PFC PSU for $27.99 for my first build. As I try to educate myself on various issues involved, I noticed that this PSU comes only with 6-pin PCI-E connectors. There are no 6+2 pin PCI-E connectors.

Question: Does not having 6+2 Pin connector a major handicap in upgradability path? To put the question in perspective, let's assume 3 year time horizon and no extreme gaming.

I googled and found that the two extra pins are just grounding pins. If you have those, overclocking is enabled, else disabled. Is that all?

 

[jonnyGURU]

Overclocking enabled/disabled?

Wrong.

At least for Nvidia cards, you can't even post without the extra two pins.

 

[MarcVenice]

My HD4850's from gainward also require 8pin pci-e connectors. The box came with a 6pin to 8pin pci-e adapter though. Not sure how recommended it is to use those, but hey, it works. So I'd say, small handicap. Running a gtx280 should be no problem. Running sli-ed videocards that need 8pin pci-e connectors with that PSU isn't recommended anyways, so no need to worry about that.

 

[VirtualLarry]

I don't get how an 8-pin (6+2) is able to handle twice the current of a 6-pin, if they still have the same number of wires carrying power, and only have two extra ground wires. Can someone explain that to me? I though that you needed additional power wires to carry current.

 

[VirtualLarry]

No-one knows the answer?

 

[jonnyGURU]

First off, it's always better to have more, or at least heavier gage, ground wires than hot wires in a DC circuit. Not sure if you've ever dabbled in high end car audio, but we do it in car stereos all day long. Remember: Even though we use the term "positive" and "negative", DC electrons actually flow from an area of negative charge to that of a positive charge.

So does an extra ground wire or two allow the connector to support more current? Sure.

Now also remember what the PCI-SIG specification actually is for the 8-pin PCIe. It really only suggests ONE extra ground for increase current. The 8th pin is actually for a +12V sense. What's supposed to happen is as current increases, resistance increases and voltage drops (V = I*R). The +12V sense is supposed to feed voltage information back to an IC in the PSU and tell it when the +12V drops out of spec. The PSU is then supposed to compensate for that resistance with an increase in voltage at the source.

For whatever reason, the +12V sense as it's laid out in the PCI-SIG specification for 300W graphics cards hasn't been implemented by a single PSU manufacturer (added cost? Market is tough enough as it is to make any money). They just put in an extra ground to "trick" the graphics card into thinking the sense is there. No actual current is flowing through this eigth wire (fifth ground wire).

Can the 8-pin PCIe connector as it's implemented today really deliver TWICE the power of a 6-pin? No f'ing way... but that's ok. Because not a single card on the market meets or exceeds even the 75W per connector specification of the 6-pin and the additional ground does seem to help enough in delivering more current (if needed). And fortunately, graphics cards are getting more efficient despite becoming more powerful, so there may never be a need for a +12V sense on a PSU.

Hope this helps.

 

[VirtualLarry]

Thats very interesting, thanks for educating me.

If it were me, I wouldn't have screwed around with a 12V sense line, I would have just specced out an additional 12V line for power, and an additional ground. Much like the ATX20 connector went to ATX24, with a few more wires of various lines to carry more current.

 

[zerocool84]

Originally posted by: jonnyGURU
First off, it's always better to have more, or at least heavier gage, ground wires than hot wires in a DC circuit. Not sure if you've ever dabbled in high end car audio, but we do it in car stereos all day long. Remember: Even though we use the term "positive" and "negative", DC electrons actually flow from an area of negative charge to that of a positive charge.

So does an extra ground wire or two allow the connector to support more current? Sure.

Now also remember what the PCI-SIG specification actually is for the 8-pin PCIe. It really only suggests ONE extra ground for increase current. The 8th pin is actually for a +12V sense. What's supposed to happen is as current increases, resistance increases and voltage drops (V = I*R). The +12V sense is supposed to feed voltage information back to an IC in the PSU and tell it when the +12V drops out of spec. The PSU is then supposed to compensate for that resistance with an increase in voltage at the source.

For whatever reason, the +12V sense as it's laid out in the PCI-SIG specification for 300W graphics cards hasn't been implemented by a single PSU manufacturer (added cost? Market is tough enough as it is to make any money). They just put in an extra ground to "trick" the graphics card into thinking the sense is there. No actual current is flowing through this eigth wire (fifth ground wire).

Can the 8-pin PCIe connector as it's implemented today really deliver TWICE the power of a 6-pin? No f'ing way... but that's ok. Because not a single card on the market meets or exceeds even the 75W per connector specification of the 6-pin and the additional ground does seem to help enough in delivering more current (if needed). And fortunately, graphics cards are getting more efficient despite becoming more powerful, so there may never be a need for a +12V sense on a PSU.

Hope this helps.

Very good read.

 

[jonnyGURU]

Originally posted by: VirtualLarry
Thats very interesting, thanks for educating me.

If it were me, I wouldn't have screwed around with a 12V sense line, I would have just specced out an additional 12V line for power, and an additional ground. Much like the ATX20 connector went to ATX24, with a few more wires of various lines to carry more current.

Sure, but rememeber this a plethora of ground wires on an ATX connector. Sure, they added an additional +12V wire, but they also added an additional ground and the load on the other rails on a motherboard that uses a 24-pin is considerably less than an older PC with a 20-pin ATX connector so even more grounds really wasn't necessary.

 

[smcinnis]

Added ground wires increase the load capability of a circuit. This is because the ground is the source of electrons for current flow. The positive is the source of the electromotive force, not the source of electrons (which is what current is based upon: the rate of electron movement across a fixed point over a period of time). So if you think of the positive side of the circuit as something like a sump, where it is drawing water (electrons) from a wide pool, larger diameter pipes (or more of them) will result in more volume capable of being drawn.

Yes, an oversimplification. But the illustration above is the best way I have thought of to explain this concept using layman's terms.