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Author Topic: 4 x 6870's Which Psu?  (Read 1429 times)
Bitcoin Swami
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August 28, 2011, 06:45:10 PM
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I'm building a rig with 4 6870's which psu would be the best without going overboard? Also will it come with enough cords to connect to them or will I have to buy something extra? Thanks

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August 28, 2011, 09:26:50 PM
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I have yet to see a quality psu that comes with enough PCIE connectots, its annnoying.

Unfortunately I can't get you hard numbers on a 6870 as my current set up with one won't allow me to underclock the mem, however 150 - 175W from the wall is probably a reasonable estimate, unless you go really crazy with overclocking, so 175*4 = 700W probable max draw from the wall. A 750Watt PSU would be a very safe buy for a normal system (dont go supwe oc'ong a high end cpu though), you could probably get away with a 650Watt PSU, but most people seem very skittish of taxing their PSUs for some reason, go figure.

The COrsair AX750 is probably the best PSU out there, but also probably overkill for your needs, but if you want the best, that's something to look at. The FSP Aurum gold 700W is a decent PSU and should be able to handle your needs while giving you Gold Efficiency at a decent sticker value. LEPA G700-MA is also in the decent category, and it's cheap with a MIR right now from the egg. Thermaltake Toughpower Grand GOld 750 also good and going for cheap.

Those are just some of what's out there, but they're all quality units with good warranties in case you get the rare defective unit and they're not bank breaking (I recommend gold rated PSUs for anyone running a 24/7 high load rig, as it will actually pay off the price difference in a reasonable period of time).
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August 28, 2011, 09:31:08 PM
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I have a 5850 and a 5870 on a 1250W PSU  Shocked
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August 29, 2011, 07:28:52 AM
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I have yet to see a quality psu that comes with enough PCIE connectots, its annnoying.

The Corsair AX750 is probably the best PSU out there, but also probably overkill for your needs, but if you want the best, that's something to look at. [..] Thermaltake Toughpower Grand GOld 750 also good and going for cheap.

Those are just some of what's out there, but they're all quality units with good warranties in case you get the rare defective unit and they're not bank breaking (I recommend gold rated PSUs for anyone running a 24/7 high load rig, as it will actually pay off the price difference in a reasonable period of time).


whenever you have PSU questions, etc or are considering a new build, http://www.extreme.outervision.com/psucalculator.jsp
I also use http://whirlpool.net.au/wiki/psu_recommendations, but, yes, 1250w should cover most sins

750w will probably not be enough to cover GPU + CPU at peak, as the general peak load looks like 769w, and 1100VA on AMD 940, 741w/1060VA on i7 2600k

but the big issue is the 12v capacity, will need to be over 58-60A to handle the PCIE load on those cards. that's what to check for.

you should aim for 850w silver/gold or 1200w bronze/silver if you want more reliability or need specific cabling.

in some places, 1200w is cheaper than 850w silver rated PSUs, but, ultimately, brand names charge more. i.e. seasonic X series = Corsair AX series, same seasonic hardware, $50 difference.

as for the bronze/silver/gold, the 80+ gold rating applies to PSU conversion efficiency, soo, if you run the PSU at half-load capacity, i.e. 300w peak load on the big sticker 750w PSU , it will use less power and cost $50-100 more than the equivalent 750w. you're pulling ~740-780w, 60-63% of 1250w, so aim for the 1200w series on a cheaper PSU, or get a modular 850w-900w PSU, both should cover the same power load and the 12v rail

that said, silver rated at 50% load, will be roughly as good as a gold rated at 85% load. that gold standard is pretty damn good. i've run a 6970 x 2 on 750w gold for 3 days, no issues, and that was somewhere around 88-90% load.
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August 29, 2011, 03:32:24 PM
 #5

I have yet to see a quality psu that comes with enough PCIE connectots, its annnoying.

The Corsair AX750 is probably the best PSU out there, but also probably overkill for your needs, but if you want the best, that's something to look at. [..] Thermaltake Toughpower Grand GOld 750 also good and going for cheap.

Those are just some of what's out there, but they're all quality units with good warranties in case you get the rare defective unit and they're not bank breaking (I recommend gold rated PSUs for anyone running a 24/7 high load rig, as it will actually pay off the price difference in a reasonable period of time).


whenever you have PSU questions, etc or are considering a new build, http://www.extreme.outervision.com/psucalculator.jsp
I also use http://whirlpool.net.au/wiki/psu_recommendations, but, yes, 1250w should cover most sins

750w will probably not be enough to cover GPU + CPU at peak, as the general peak load looks like 769w, and 1100VA on AMD 940, 741w/1060VA on i7 2600k

but the big issue is the 12v capacity, will need to be over 58-60A to handle the PCIE load on those cards. that's what to check for.

you should aim for 850w silver/gold or 1200w bronze/silver if you want more reliability or need specific cabling.

in some places, 1200w is cheaper than 850w silver rated PSUs, but, ultimately, brand names charge more. i.e. seasonic X series = Corsair AX series, same seasonic hardware, $50 difference.

as for the bronze/silver/gold, the 80+ gold rating applies to PSU conversion efficiency, soo, if you run the PSU at half-load capacity, i.e. 300w peak load on the big sticker 750w PSU , it will use less power and cost $50-100 more than the equivalent 750w. you're pulling ~740-780w, 60-63% of 1250w, so aim for the 1200w series on a cheaper PSU, or get a modular 850w-900w PSU, both should cover the same power load and the 12v rail

that said, silver rated at 50% load, will be roughly as good as a gold rated at 85% load. that gold standard is pretty damn good. i've run a 6970 x 2 on 750w gold for 3 days, no issues, and that was somewhere around 88-90% load.

Whenever you have PSU questions, the last thing you should ever do is consult an online PSU calculator. outervision is good, but not that good.

What you should do is find what a card actually draws as I did and plan accordingly. 750Watts is beyond enough, arching on to overkill territory. Wall power draw is not the same as system power delivery, that's what efficiency relates to. These are 6870s not 6970s

If you can find a *quality* 1200W for cheaper than a *quality* 750W, and come up with the same efficiency then by all means go ahead, but I've not seen that math work out very often. I don't know of any 1200W PSU that retails under $200, while you can find plenty of gold rated 750W PSUs for nearer $100 than $200. But feel free to shop around.
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August 29, 2011, 04:36:36 PM
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I have a 5850 and a 5870 on a 1250W PSU  Shocked

Talk about MASSIVE overkill. You could stick another 5850 and another 5870 without problems.
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August 30, 2011, 02:14:28 PM
 #7

I have 2x 6870's on a 650w PSU with no issue. I imagine you could probably get away running them on a 900w or better PSU without issue since each card is ~150w TDP
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August 30, 2011, 03:22:23 PM
 #8

Get a Corsair TX850V2, 840W on 12V rail and 70A, you'll have space to overclock too if you'll go with a cpu that doesnt that much power (or you won't stress it too much).
It's got 4 6+2 Pin power connectors, so you can connect either 4 hd6850s or 2 6870s and and remaining 2 from a molex-pcie connector.

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August 30, 2011, 07:20:05 PM
 #9

I have a 1200 watt PSU running 4 6870s right now, I think at most they use 760 watt and that is including the CPU and motherboard. I have an 800 watt PSU I might end up using for them at some point but my biggest problem is finding a PSU with enough molex, really.

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August 30, 2011, 09:10:40 PM
 #10

I'm running 2 rigs with 4 6870's each overclocked using an Antec 900W 80plus bronze I got from newegg for 90.00US after rebate.
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