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Author Topic: Hardware question  (Read 596 times)
barwizi
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June 19, 2013, 12:57:01 PM
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What's the advisable power supply for 4 7970s?
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anderl
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June 19, 2013, 01:02:43 PM
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if you undervolt 1200 watts.  but 1500 is recommended.
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June 19, 2013, 01:07:52 PM
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^ Nonsense. I don't undervolt and they're running fine on a 1250W PSU. It draws max 1240W from the wall on 4 OC'd HD7970's, AMD X2 and 4 GB of ram. With 91% efficiency, that's 1130W on the 12V side of the PSU. That's 120W of headroom @ full load, which is plenty.

No need for a 1500W PSU on 4 7970's.

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June 19, 2013, 01:26:55 PM
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I manage to run 2 7970 on a 600W PSU, with some (not much) headroom, so 1200W or 1250W should be enough.

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June 19, 2013, 01:40:44 PM
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^ Nonsense. I don't undervolt and they're running fine on a 1250W PSU. It draws max 1240W from the wall on 4 OC'd HD7970's, AMD X2 and 4 GB of ram. With 91% efficiency, that's 1130W on the 12V side of the PSU. That's 120W of headroom @ full load, which is plenty.

No need for a 1500W PSU on 4 7970's.

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Might want to check your math. That's 10w of headroom.
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June 19, 2013, 01:57:55 PM
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So, too lazy or too stupid to find the correct sub forum I guess? I mean it IS sort of hard to find the HARDWARE sub forum.. Not like its listed in main forum...
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June 19, 2013, 01:58:05 PM
Last edit: August 01, 2014, 10:24:51 PM by aa
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.

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June 19, 2013, 02:00:25 PM
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^ Nonsense. I don't undervolt and they're running fine on a 1250W PSU. It draws max 1240W from the wall on 4 OC'd HD7970's, AMD X2 and 4 GB of ram. With 91% efficiency, that's 1130W on the 12V side of the PSU. That's 120W of headroom @ full load, which is plenty.

No need for a 1500W PSU on 4 7970's.

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PSU loses around 3% of its power/year because of aging capacitors. Also, you should be running PSU at around 85% of its max power. The closer you go to maximum, less efficient it becomes.


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June 19, 2013, 02:52:09 PM
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^ Nonsense. I don't undervolt and they're running fine on a 1250W PSU. It draws max 1240W from the wall on 4 OC'd HD7970's, AMD X2 and 4 GB of ram. With 91% efficiency, that's 1130W on the 12V side of the PSU. That's 120W of headroom @ full load, which is plenty.

No need for a 1500W PSU on 4 7970's.

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Might want to check your math. That's 10w of headroom.

The wattage of a power supply is how much it delivers, not how much it draws. If a machine with a 1250 watt PS is drawing 1240 at the wall but is 90% efficient, it is delivering about 1116 watts of power to the PC. So, if a 90% efficient 1250 watt PS is drawing 1240 at the wall it still has an additional ~134 watts or so of available power. Conversely, at maximum power delivery of 1250 watts, one could expect to see about a ~1375 watt load at the wall. I wouldn't run anything that close to the rated power though, but that's just me. Even within 10% is a bit too close, I prefer at least a 15-20% margin. Don't need anything going POOF! on my machines, ya know?
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June 19, 2013, 10:17:01 PM
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^ Nonsense. I don't undervolt and they're running fine on a 1250W PSU. It draws max 1240W from the wall on 4 OC'd HD7970's, AMD X2 and 4 GB of ram. With 91% efficiency, that's 1130W on the 12V side of the PSU. That's 120W of headroom @ full load, which is plenty.

No need for a 1500W PSU on 4 7970's.

LKKy4eDWyVtSrQAJy7Qmmz61RaFY91D9yC

PSU loses around 3% of its power/year because of aging capacitors. Also, you should be running PSU at around 85% of its max power. The closer you go to maximum, less efficient it becomes.


my2c

Assuming what you say is true (as you post no source whatsoever), you can run it at least 3 years before you reach it's rated sustained maximum output. Running 4 7970's on a 1250W psu is running it on 90% of it's maximum - completely acceptable.

Efficiency does not deviate significantly from it's norm as it reaches its maximum. Most gold-standard PSU's have an efficiency of ~92% @ 50% load and an efficiency of ~90% @ full load (source). Not significant at all.

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