Achieving more than 300 watts through a 6 pin and a 8 pin?

[cbn]

http://www.guru3d.com/article/overclock-radeon-5970-guide/3

According to this Guru of 3d HD5970 overclocking review they were able to squeeze 380 watts through a 6pin/8 pin power connector combination.

On the first page of the review it mentions needing enough amps on the 12v rail.

Is there a formula for determining how many amps are needed to exceed the 300watt limitations of a 6pin/8pin?

A 1200 watt PSU was used in the test but I would hope something much smaller could be used to obtain the same result.

 

[HOOfan 1]

Unless they used some kind of shunts to sense the current, I am not sure how they figured they are drawing 380W from the card. The 300W limit encompasses the 6pin 8pin and the PCI-E socket itself. Xbit labs does just that and found a normal HD5970 tops out around 205W.

75W for the 6 pin, 150W for the 8 pin and 75W from the slot for PCI-E 1.0...although I believe the 2.0 specs allow 150W from the slot.

Of course Power(watts)=Potential(Volts i.e. 12V) * current(amps)

So the supposed 380W is about 31A.

But that will be divided between 3 sources...and possibly 3 separate rails. The bias will be to pull more power from the PCI-E connectors instead of the PCI-E slot.

 

[cbn]

Unless they used some kind of shunts to sense the current, I am not sure how they figured they are drawing 380W from the card. The 300W limit encompasses the 6pin 8pin and the PCI-E socket itself. Xbit labs does just that and found a normal HD5970 tops out around 205W.

75W for the 6 pin, 150W for the 8 pin and 75W from the slot for PCI-E 1.0...although I believe the 2.0 specs allow 150W from the slot.

Of course Power(watts)=Potential(Volts i.e. 12V) * current(amps)

So the supposed 380W is about 31A.

But that will be divided between 3 sources...and possibly 3 separate rails. The bias will be to pull more power from the PCI-E connectors instead of the PCI-E slot.

I think PCI-E 2.0 slot still only pulls 75 watts max.

Seriously drawing 380 watts through lines that are only meant to handle 300 watts....Is that really safe?

 

[HOOfan 1]

I think PCI-E 2.0 slot still only pulls 75 watts max.

Seriously drawing 380 watts through lines that are only meant to handle 300 watts....Is that really safe?

Combined they can handle more than 300W

 

[cbn]

Combined they can handle more than 300W

What sort of penalty occurs when this happens?

75 watts for PCI-E slot + 75 watts for 6 pin + 150 watts for the 8 pin equals 300 watts total. (This according to your previous post)

 

[HOOfan 1]

What sort of penalty occurs when this happens?

75 watts for PCI-E slot + 75 watts for 6 pin + 150 watts for the 8 pin equals 300 watts total. (This according to your previous post)

As far as I know, none. I think the onus is on the graphics card makers to make sure the PCI-E connectors are within spec...not the power supply.

 

[Modelworks]

The main number with connectors is always amps. Watts is really a useless rating for this type of thing. The connectors on one video card I have are rated at 48VDC @ 20A which would make some think that means it can handle 960 watts, but that isn't how it works. Put 12VDC@80A on that connector and it will fail. The current rating of the connectors are based on how thick the metal is that is doing the connecting, while the voltage rating is based on how well the plastic insulates the voltage.

One thing I have noticed is people assuming that because the supply says 60A that they can run 60A off a connector, that is false. The wiring coming out of the supply is not sized to allow all the current on one wire which is why you have so many wires running to the video card rather than just a + and - . Having one thick wire cost more and is harder to work with than multiple small wires. That is the reason it was increased from 6pins to 8pins , it allows another pair of wires to carry the current.

 

[jvroig]

75W for the 6 pin, 150W for the 8 pin and 75W from the slot for PCI-E 1.0..

Combined they can handle more than 300W

I don't doubt you at all, but can you explain how this adds up? The individual power that the connectors can supply only add up to 300W (75 + 150 + 75) but when combined they can handle more than 300W? How does this happen? Is it because the slot can actually draw more than just 75W?

 

[HOOfan 1]

Those are the limits set by PCI-E SIG. When combined the 18 AWG wires for the PCI-E connectors can handle more current though. The cards are designed not to pull more than that. Apparently these reviews are saying if you increase the volatge the cards will pull beyond the PCI-E SIG specification.

 

[Ayah]

TDP for the 5850 is something like 151W.
And since a 5970 is essentially 2 5870s taped together and downclocked to 5850 speeds..