Power Supply Calculation Question

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AugmenTab

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Feb 17, 2014
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I'm building a computer with an AMD FX 4130 CPU, one 4GB stick of DDR3 RAM, four R9 270 graphics cards, and two powered risers. I used the eXtreme PSU Calculator that often gets recommended on this board, and it determined that I need a PSU of at least 760W output.

I'm led to believe that, because of this, an 850W PSU should be able to power all of the parts with no issues, but this seems unlikely. I feel as though it should be higher, probably at least 1000W. Can anyone here shed some light on this? I'd rather not screw up such an expensive (for me, at least) computer.
 
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Ok., so i totally missed that you are using 4 of them, and i am sorry about that. BUT each 270 does NOT use over 200 watts each.http://www.guru3d.com/articles_pages/amd_radeon_r9_270_review,8.html
each uses roughly 150 under gaming load. you don't get into higher power consumption until you get a 280x or gtx 770.

also the link that Jeremy listed shows total system power consumption with a 270 installed at 270 watts, which means that the 270 watt number is a total of the whole system, not just the 270 alone

for a psu you need to look at the 12v rails and the amperage on each. wattage is calculated as amps x voltage, so make sure you get a psu with either multiple 12v rails that have enough amperage to = 150 ish wattage per gpu...
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Brantyn Gerik

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For that config you could get away with a quality 650 watt psu (i could recommend lower, but people will give flack, plus it's safe to go at least a bit higher). That system might use maybe 350 watts under FULL artificial load. So you have been misled to what you actually need, but i wouldn't undershoot by too much. I'd say you'd be fine with anywhere from a 600 watt and up psu
 
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EasyLover

EasyLover

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Single 270 pulls 270-280W on high load where as roughly it pulls 107W on idle (Source: Various benchmarks). You're going to use four of them on a single system. 650W may not be able to satisfy the power requirements of the complete system.

There are two power hungry components in system CPU and GPU in your case (Four GPUs). They are connected using ATX12v/EPS12v on the PSU.

As a general rule, always look for PSU that gives you higher Amps on +12v rail(s). Just don't simply look at 600W or 750W. Check the load under +12v rail. This info is mentioned on the label on the PSU or the specs quoted by the manufacturer.

In you case you should have 50+Amps on +12v rail(s). This should be your criteria. Even in wattages you will require 800W+ PSU.

Yes system does not darw or pull its stated maximum power.
 
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Brantyn Gerik

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Ok., so i totally missed that you are using 4 of them, and i am sorry about that. BUT each 270 does NOT use over 200 watts each.http://www.guru3d.com/articles_pages/amd_radeon_r9_270_review,8.html
each uses roughly 150 under gaming load. you don't get into higher power consumption until you get a 280x or gtx 770.

also the link that Jeremy listed shows total system power consumption with a 270 installed at 270 watts, which means that the 270 watt number is a total of the whole system, not just the 270 alone

for a psu you need to look at the 12v rails and the amperage on each. wattage is calculated as amps x voltage, so make sure you get a psu with either multiple 12v rails that have enough amperage to = 150 ish wattage per gpu, as well as factor in the roughly 100-140 watts from the rest of the system seperate from the gpu's.

I will fully admit to unselecting the best answer PURELY based on him being downright wrong about the power consumption of the 270
 
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jeremyp79

jeremyp79

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Not a problem, I misread the power consumption, it was for the total system, not just the video card. My apologies.
 
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Brantyn Gerik

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No worries, just trying to make so no miscommunication happens. Of course overspending on the psu is always recommended however, as the psu is one of the most underrated parts of a build in most cases. In my opinion, the psu is almost equally as important to the whole build as even the gpu and cpu; because the psu is technically the life of your whole build, i think the psu is the one part that it is actually encouraged to overspend on, whereas with other things, like an i5 vs i7, overspending may not always be wise. :) No worries at all Jeremy, Your answer was still very insightful :)'

as far as what OP needs for 4 of them (4x 270 GPUs), i've had a little bit too much to drink to competently calculate power usage (yay for the first part of reading week for students), but rule of thumb, make sure it is the 12v rail that is supporting each card, and if i really had to make a recommendation, i would suggest a multi 12v rail psu with a 12v x amperage rating that = say 200 per card for safety overhead (12v x amperage gives you your allotted wattage). So either get a psu with say 2 really strong 12v rails, or get a psu with 3-4 less powerful 12v rails. (cougar is a good brand if you decide for multiple less powerful 12v rails)
 
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EasyLover

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I would recommend tier-1 EVGA PSU. If could not get one then try XFX, Seasonic as well. Well reputable brands.
When going for multi-rail (virtual rail) design just don't assume that by simply adding the power (W) on each rail will give you a good idea of total power (W) on these rails. Actual power (w) would be less than this sum. Check the PSU Label.

PUS is not a cost but an investment to protect the components of the PC. Pl treat it as such.
 
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qbsinfo

qbsinfo

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FYI it is NEMA standard that when given a continuous 100% load (some debate continuous as being 8 or 12 hours) that you "de-rate" the supply by 80% since you are mining i assume 24/7 i guess it fits in the criteria.

in other words if you need 760 watts then 760/.8 = 950 watts <-- that is the minimum size you are looking for. also i know AlphaC on OCN. you can take what he posts to the bank. however please notice that those power figures are with the cards undervolted.


cheers.
 
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