Radeon 4870 CrossFireX

[DAVco]

My brother has recently upgraded his graphics card, so now I am the proud owner of (another) AMD Radeon 4870. My machine is already running exactly the same card, so I was wondering if it would be worth setting up a CrossFireX configuration?

The one concern that I have is whether or not my power supply would be able to handle such a setup; I have a Corsair TX650w Specs here. According to the AMD website, they recommend at least 600w for a dual 4870 configuration so I think I'm OK on that front, however I am also running a Core i7 920 and three 3.5" hard disks (I could probably get by with two if needed) - would this be pushing my PSU a bit too far?

Cheers

 

[beltzy]

You'd probably be fine. Note that your PSU only has 2 6-pin PCI-e power connectors and each 4870 requires 2. However, you can work around it by using the MOLEX to PCI-e converters that often come with the cards (they take 2 MOLEX inputs and switch it to a PCI-e slot). Normally I'd recommend to people that they not use these converters, but since you already have all the hardware I'd try it out and test it out (using them IS a manufacturer supported way to power the cards provided your PSU can handle it). That's a solid PSU; let us know how it goes!

 

[DAVco]

I've just dug out the molex-to-6-pin connectors that came with the PSU and they both have just a single molex connector, whereas most other adapters I've seen have two (apparently connecting each to a different rail provides more stable voltage?). I'm sure they'll be fine since they are the adapters which came with the PSU, but you can never be too cautious - I've fried a few (cheap, crap) PSU's in my time

I guess I should benchmark before and after too - just out of curiosity. What is the standard graphics benchmarking tool these days?

 

[dechy]

Depends on if you OC everything you have or not. My old Oc'ed E8400 @ only 3.6GHz + 2 Raptors + XXX 4870 (Oc'ed version from XFX) + 8GB RAM hit ~420W peak. I checked wattage use through APC Powerchute.

i7 920 even stock clocks needs more power, and a second 4870... ish.

That PSU sounds a bit on the underpowered side

 

[need4speeds]

I was running a corsair CX600, two 4870's, A6-3650@3.5ghz and it ran fine. Passed prime-95 and furmark testing.
I swapped for a ocz fata1ly 550 because it has two 25 amp rails instead of the corsair's single 40 amp rail.
Both power supplies work fine with that system.

You will need two molex to pcie adaptors.

Your corsair has a single 52amp 12volt rail, it should be fine.

 

[need4speeds]

Try and plug the adapter to the first molex plug closest to the power supply. The shorter the wire the lower the voltage drop in the wire.

 

[DAVco]

Well, I'm very pleased with the results - Near as makes no difference double the framerate in the Unigine benchmark!
Everything running at stock clocks, by the way.

Single Radeon 4870
Dual Radeon 4870 CrossfireX

System seems stable and running at normal temperatures, bar a slight increase on one of the cards which now has slightly reduced ventilation. I have no way of measuring power consumption, but nothing bad happened during stress tests, so everything is full speed ahead!

 

[need4speeds]

http://www.geeks3d.com/20090618/graphics-cards-thermal-design-power-tdp-database/

The 4870 is about 157 watts or 13 amps. The system with the cpu/board/drives about 180 watts but some of that power is 5volt and 3.3volt power so you can subtract about 50 watts. 130 watts for the system or about 11 amps.
13+13+11 amps = 37 amps. Yes that is cutting it close on my smaller corsair CX600, but you have a extra 12 amps on your larger corsair.
Your corsair should run three 4870's at stock clocks just fine.

You are better off overclocking the cpu and leaving the 4870's at stock clocks.

Well anyways, i'm glad it is working fine.

 

[need4speeds]

P(watts)=I(amps) x E(voltage)

I=P/E

E=P/I