Vid card power Q

OldBuzzard · Apr 15, 2008, 07:22 PM

OK, my 3870 x2 should be here tomorrow, and I have a question about getting power to it.

It needs both a 6-pin and an 8-pin input.

My 620HX has 2 Pci-E power leads. BOTH have a 6-pin and an 8-pin.

Which would be better?

1. Use the 6-pin and 8-pin off of one cable?

2. Use both cables, and the 6-pin off of one, and the 8-pin off of the other?

I'd prefer option 1 as that will make cable management easier.

Anyone have any advice for this?

**ChaosMinionX** · Apr 15, 2008, 07:30 PM

Use the same lead... with the 6pin and 8pin... there is no need to run 2 separate lines into your card as the power its receiving will be identical.

Judas · Apr 16, 2008, 11:12 AM

really?

thought it would be much better and reliable to run 2 different leads if possible...

tcman · Apr 16, 2008, 12:26 PM

If I am right the Corsair 620HX got actually a single rail of 12V (50 amps), so you should not have a problem by using the 6-pin and 8-pin off of one cable. The psu is capable of powering up two HD2900XTs in Crossfire which require more power than one HD3870X2, while one HD2900XT require almost the same power as one HD3870X2. Maybe the HD2900XT uses 20-30 watts less than the HD3870X2 at load. So, ATI-AMD has significantly improved the power requirement by using a smaller die size for the HD3870X2.

swimtech · Apr 16, 2008, 12:56 PM

So, let's say the 3870x2 draws 156 watts at max load (made to be divisible by 12 and closely adhering to the figure the Extreme Power Calculator specifies for this card, stickied in this forum - thanks!)...

That's a draw of 13 amps on the 12Vdc line.

The wire gauge for those yellow wires is 18, capable of handling approximately 10 amps on each wire ( the reference I used and agree with, mostly... ) and there are three of them on the PCIe 6 pin connector. That gives a delivery capacity of 30 amps (360 watts, theoretically) on that one wire set. Electrically speaking, using both connectors on the one wire set to power a 3870x2 should be fine.

I would be a bit cautious about running crossfired 2900XTs off the one line though, unless the wire gauge with that Corsair supply to the PCIe connectors in use is lower than 18. Those two cards together draw about 260 watts! I'd want a little more amperage headroom on the wire set...

Interesting question!

Matth · Apr 16, 2008, 03:06 PM

Reading one review, it appears the power draw may be 170-180W (2x a normal 3870 at up to 80W, plus some additional overhead for the interconnect components).

The 8pin PCI-E 2.0 has a load rating of 150W.

Unless really awkward, I would use both power cables, to ensure that voltage drop is kept to a minimum, just as I woulkd try to ensure as good a balance as possible on a PSU with multiple 12V rails, even if not threatening to exceed rating on any rail.

OldBuzzard · Apr 17, 2008, 04:34 AM

Turned out I was wrong about those cables...each one has only 1 connection, so I had to use both

Sometimes I just ain't real bright

Anyway, got that rascal installed. GAWD is it HUGE! Makes my old 1950GT look like the 98 lb. weakling of comic book fame! Damned sure glad that I upgraded to the CM690, cause that puppy would have never fit inside the Centurian 5 that it replaced.

Installing it was pretty easy, but the drivers took some time, as I hadOperating Systems to change. Gonna wait till tomorrow or the nest day to actually stress it, or maybe even after the weekend, as I'm picking up 8 Gigs of RAM on Sat. Should make the Cinematic Mod for HalfLife2 quite playable