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Author Topic: PSU needed for 3 x HD 7970  (Read 1354 times)
surphactone
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May 31, 2013, 05:11:30 PM
 #1

Hi
which PSU should i buy to run 3 x 7970 , how many watt ?

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fflewddur
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May 31, 2013, 06:10:10 PM
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I'm running four with a Corsair 1200AX, but you could get away with less. I'd recommend the Corsair AX860i; it's 860 watts and super efficient. Mine is powering two 7950s and never draws more than 415 watts... should be plenty of headroom for three 7970s, especially if you undervolt them a bit.
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May 31, 2013, 06:22:46 PM
 #3

Hi
which PSU should i buy to run 3 x 7970 , how many watt ?

850 watts minimum, if you do go with an 850 watt it better be a quality one with some nice beefy rails.
diskodasa
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May 31, 2013, 06:26:03 PM
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At least 1500W because of this http://www.amd.com/us/products/desktop/graphics/7000/7970/Pages/radeon-7970.aspx#2
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May 31, 2013, 07:01:12 PM
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Whoa there buddy 1500w is excessive even a 1000w power supply is more than enough.
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May 31, 2013, 07:35:06 PM
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There's absolutely no need for a 1500 watt PSU to run three 7970s. Around 850 will work, but power supplies are a great example of getting what (watt?) you pay for. Just because a PSU draws 850 watts from the wall doesn't mean it converts all of that into usable DC electricity. A cheap one may only only work at 70% efficiency, which leaves you with ~595 watts; a better (read: more expensive) 850 watt PSU should work around 90% efficiency, and give you a clean 760 watts, which is plenty to power three 7970s.
surphactone
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May 31, 2013, 09:44:20 PM
 #7

thanks all  Grin
i will go for a good 850 watts one  Tongue

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June 06, 2013, 12:46:51 PM
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thanks all  Grin
i will go for a good 850 watts one  Tongue

Any news on 850W PSU with 3 gpu-s? Is it working? Stable...?
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June 06, 2013, 02:29:21 PM
 #9

I'm running four with a Corsair 1200AX, but you could get away with less. I'd recommend the Corsair AX860i; it's 860 watts and super efficient. Mine is powering two 7950s and never draws more than 415 watts... should be plenty of headroom for three 7970s, especially if you undervolt them a bit.

Hi, about these 415 watts how did you achieve that? It seems very good, considering each 7950 as 200W. Is this from wall - do you use some kill-a-watt? Or is this number from Corsair software provided with AX860i?
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June 06, 2013, 02:33:31 PM
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800-900 watts is perfect.
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June 06, 2013, 02:37:35 PM
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PSUs are most efficient at the 80-90% range. So you'll want a 800-850W PSU.

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Alexander The Great
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June 06, 2013, 02:40:27 PM
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PSUs are most efficient at the 80-90% range. So you'll want a 800-850W PSU.

Yes I agree
JohanS
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June 06, 2013, 03:04:42 PM
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thanks all  Grin
i will go for a good 850 watts one  Tongue

Nice!

GL
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June 06, 2013, 03:26:52 PM
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any one of them will do the trick
Eva Braun
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June 06, 2013, 03:49:45 PM
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yes anyone of those will do the trick
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June 06, 2013, 04:01:18 PM
 #16

800W of 12v min for sha, and ~900+ of 12v for scrypt
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June 06, 2013, 04:07:47 PM
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800W of 12v min for sha, and ~900+ of 12v for scrypt

I own a 800W, works like a charm
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June 06, 2013, 05:06:02 PM
 #18


AMD publishes PSU requirements like this because if they said PSU must be able to deliver ~20A on +12V rail nobody would understand what they mean ; )
Also because PSU manufacturers often lie about their PSU specs.

I'm running 3x7950 + 2x6950 mining LTC with Enermax 1250W works fine. One of 7950 was even using ~320W until I've noticed it and lowered voltage.

PSU = Power Supply Unit ; )

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June 06, 2013, 05:15:07 PM
 #19

sorry but what does PSU stand for?

Power supply unit
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June 06, 2013, 05:21:16 PM
 #20

why does scrypt requires more power than sha-256?  because we need more ram for scrypt?  thank you.   Huh

800W of 12v min for sha, and ~900+ of 12v for scrypt
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