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Author Topic: Will 3x 5850 work on a 750 watt  (Read 5748 times)
Reckman
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July 27, 2011, 07:52:57 PM
 #1

Anyone done this
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KKAtan
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July 27, 2011, 07:58:18 PM
 #2

I'm fairly certain they will. And if the PSU doesn't have enough pci-e power plugs, the graphics cards always have power plug converters.

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amazingrando
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July 27, 2011, 08:00:25 PM
 #3

I don't know about the power draw with 5850's, but with three 6950's and a sempron 140 i draw about 750W.  If the power draw is similar, you could do it, but as you get closer to the max output of the PSU the power might not be as clean and you lose efficiency, not to mention that it might cause too much heat/wear out the PSU over extended use. I would use at least 850W in your config unless the 5850's use a lot less power than the 6950's.

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cicada
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July 27, 2011, 08:01:33 PM
 #4

5850's should have a TDP around 150W

150W * 3 = 450W

Unless the rest of your PC is somehow slurping down 300W you'll be fine.  Accounting for the rest of an 'average miner' system - low wattage CPU, mainboard, 1 or 2 sticks of RAM and maybe an HDD, it shouldn't be pulling more than 100W without the cards.

This should put you right in the sweet spot of that 750W PSU's efficiency.

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Meatball
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July 27, 2011, 08:12:23 PM
 #5

The key is how many rails your power supply has.  If it's a single rail unit, then, yeah, most likely.  If it's 2 or more, then maybe not since power gets split up differently along the rails and there may not be enough on the rails powering the PCI express/peripheral plugs.
TerraformProjectAlpha
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July 27, 2011, 08:14:21 PM
 #6

I had 6 card rigs and they pulled just over 1000 watts so you should be good.
cicada
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July 27, 2011, 08:21:22 PM
 #7

The key is how many rails your power supply has.  If it's a single rail unit, then, yeah, most likely.  If it's 2 or more, than maybe not since power gets split up differently along the rails and there may not be enough on the rails powering the PCI express/peripheral plugs.

True true.

Does OP want to tell us which 750W PSU so we can give a more specific answer?

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Dargo
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July 28, 2011, 02:22:34 PM
 #8

You do want a single rail, but I've got a 2x5850 rig pulling 400watts from the wall, so it would be no problem to add a third with 750w.
neo1999
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July 28, 2011, 04:24:57 PM
 #9

If the PSU has multiple rails, it's best to split up the PCIE power connectors between the rails, to even out the power draw.

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Reckman
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July 28, 2011, 04:54:30 PM
 #10

http://www.newegg.com/Product/Product.aspx?Item=N82E16817709021&nm_mc=TEMC-RMA-Approvel&cm_mmc=TEMC-RMA-Approvel-_-Content-_-text-_-

Bought this one, ended up getting my whole base system with a nice 3x full pcie for only 240 dollars =)
Meatball
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July 28, 2011, 07:39:10 PM
 #11

That one has two power rails.  You might want to reach out to their support and see if they can tell you what plugs are powered by what rail.  I've seen dual PSU's where they split the power between the rails, but one rail has just the motherboard plugs and the other rail has all the peripheral plugs.  If that's the case, you're looking at about 375W per rail on that PSU and that could be your problem.  Those 3 5850's will need more then 375W
Syke
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July 29, 2011, 10:21:10 PM
 #12

http://www.newegg.com/Product/Product.aspx?Item=N82E16817709021&nm_mc=TEMC-RMA-Approvel&cm_mmc=TEMC-RMA-Approvel-_-Content-_-text-_-

Bought this one, ended up getting my whole base system with a nice 3x full pcie for only 240 dollars =)
With only 4 pci-e connectors, how do you think you'll power 3 cards?

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drgr33n
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July 29, 2011, 10:30:20 PM
 #13

Your pushing it Cheesy 80+ power supply is only guaranteed to give you 80% that's 600w. Going back to what cicada said 150W * 3 = 450W thats only leaving you 150w for your system. Dooable yes but it might not be stable. Running a headless linuxcoin node with 4 x 5850 its pulling 675w so you might be ok.
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July 29, 2011, 10:38:24 PM
 #14

I will bought:
Corsair HX850w. It seems to have 6x 6+2pin
Asus 5850 top x3
Gigabyte GA-990FXA-UD3

it's ok?

http://www.hardwarecanucks.com/forum/hardware-canucks-reviews/21613-corsair-professional-hx850-850w-power-supply-review-2.html

cicada
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July 29, 2011, 11:12:09 PM
 #15

Your pushing it Cheesy 80+ power supply is only guaranteed to give you 80% that's 600w.

This is a common misconception - the 80% rating is an efficiency measurement only.

If you have a power supply rated for 750W, it should deliver 750W.  

The rating means it will supply that 750W with 80% efficiency.  This does not mean it can only deliver 600W to your PC.  This means it will be pulling up to 940W at the wall.  

80% of 940W is ~750W delivered.

At 100% efficiency, 750W at the wall would be 750W delivered.

At 60% efficiency, 1200W !! at the wall would deliver 750W.

With an 80+ Gold (87% minimum), ~860W at the wall would deliver 750W.

Make sense?


These numbers are all absolute minimums, real world efficiencies will trend higher usually.

All of that said, it's better to err on your side of the equation.  Loading a 750W PSU with only 600W means you won't blow the PSU or burn your house down Wink


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cicada
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July 29, 2011, 11:24:19 PM
 #16

I will bought:
Corsair HX850w. It seems to have 6x 6+2pin
...

it's ok?

The Corsair HX and TX series power supplies are awesome, I'd get them any time.

I have an HX750 (750W) powering two 6950s and two 5830s right now - it's right up at the max-fill line (740W at the wall), and it's definitely warm, but it's handling it with shining colors.

Note that this is bad to do long term, I'm adding Corsair CX430s to supplement soon.  At max, any PSU is going to produce a lot of heat and waste power, and likely shorten it's lifespan.

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