Power Issues

The new Radeon HD 2900 XT requires two extra power connectors – as its chip is still manufactured under 80 nm process, it has a typical power consumption of 215 W and AMD recommends at least a 500 W power supply for this baby (750 W if in CrossFire configuration) – however AMD certified some 400 W units to be used with this new video card. A list of certified power supplies can be found here.

The problem is that the second power connector is an 8-pin PCI Express auxiliary power connector specified by the new PCI Express 2.0 standard, and almost all power supplies don’t have this power connector yet. That is why AMD is releasing together with this video card a list of “approved” power supplies, with some manufacturers releasing “special” units for this video card today.

ATI Radeon HD 2900 XTFigure 4: Power connectors on Radeon HD 2900 XT.

To make things worse, this new 8-pin connector resembles a lot the 8-pin power connector used by motherboards, called EPS12V. The problem is that the wires on the 8-pin PCI Express auxiliary power connector is reversed in comparison with the EPS12V connector: where on the first is the ground wires, on the second is the +12 V wires and vice-versa. In other words: if you manage to install the EPS12V connector on you video card you may burn the card, the power and other components (we hope the short-circuit protection from your power supply will prevent this disaster).

In Figure 5 you see an EPS12V compared to a 6-pin PCI Express auxiliary power connector. See how the positions of the black and yellow wires are reversed. Also see how on our EPS12V connector there was a sticker saying “CPU only” (this cable was taken from a Galaxy 1,000 W power supply from Enermax). Not all power supplies come with this sticker or any other warning label.

ATI Radeon HD 2900 XTFigure 5: EPS12V vs. PCI Express auxiliary power connector.

Of course in theory the EPS12V connector doesn’t fit the 8-pin socket on the video card, however we found out that depending on how your EPS12V connector is built this installation is in fact possible. In Figure 6, you can see that we were able to force an EPS12V into the 8-pin auxiliary power connector on our Radeon HD 2900 XT. This was possible because our EPS12V connector was divided into two 4-pin connectors. The power supply used here was a Zalman ZM600-HP.

ATI Radeon HD 2900 XTFigure 6: EPS12V connector installed on the video card. DON’T DO THIS.

If your power supply doesn’t provide this new connector, you may improvise by using two 6-pin PCI Express auxiliary power connectors, as shown in Figure 7.

ATI Radeon HD 2900 XTFigure 7: Improvising by using two 6-pin PCI Express auxiliary power connectors.

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.