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Do my 6850's need to be on separate power cables?

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  • Power Supplies
  • Cable
  • Power
  • Components
Last response: in Components
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June 20, 2011 9:06:47 PM

Warning: This is a rather anal-retentive post, so only super psu nerds need bother reading.

I have an Antec Earthwatts 750W that I will use to power two 6850's. The unit has four 12v rails, each at 25 amps. The cables for the unit are connected to the rails as follows:

12V1 has 3 cables with:
- ATX connector 20+4 pin
- 5.25" Drive 3
- 3.5" Drive connectors 1 (shared with the 5.25)
- SATA 3

12V2 has one cable with:
- 8 pin EPS12V 1
- 4 pin ATX12V 1

12V3 has one cable with:
- 6+2 pin PCIe 1
- 6 pin PCIe 1

12V4 is one modular cable with:
- 6+2 pin PCIe 1
- 6 pin PCIe 1

The first three sets of cables are hardwired, while the last one is modular. I left out the non-12v cables for brevity.

My question is: If I want each of my cards to get a minimum of 25 amps (ignoring the question of whether or not they need that much), can I run my 6850's off the 12v3 cable (they only need one 6 pin each), or do I need to make use of the modular cable?

Here's where the anal-retentiveness part comes in. I could obviously play it safe and use the modular cable anyway, but I'd prefer to leave it out in order to keep the case less cluttered.

Apolgies in advance if this answer is already stickied somewhere. I looked at quite a few posts and didn't see anything about this.

More about : 6850 separate power cables

a c 716 ) Power supply
June 20, 2011 9:17:46 PM

I would run them on separate cables since you get a better load distribution on the PSU + why take a chance of starving the cards of power.
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June 20, 2011 9:48:23 PM

I agree with rolli59. I would have ran them on seperate rails. If you run them both on the same rail, they have to share that rail's 25amps. To give them each 25amps available, they need to be on seperate rails. Search for 6870 amperage and you should be able to see how many amps they use under load. Actually, I just googled myself and apparently reference 6850's max out at about 11A. So crossfired they'd max out at about 22A. Technically you'll be just fine with both of them on the same rail.
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June 20, 2011 9:51:36 PM

Ok, I was just making sure that the rails were actually physically separated, so the cable that I used mattered. I didn't know if maybe all of the 12v rails just dumped into the same place and shared amps. Thanks guys.
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June 20, 2011 9:52:15 PM

Best answer selected by grody.
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