Wattage Calculator + PSU Recommendation

[Guest]

So using about 3 different Wattage calculators, I seem to get extremely different results. Newegg tells me roughly 800w-900w PSU required, and extreme.outervision's wattage calc. tells me only 650-700w. This confuses me quite a bit since I made sure my results were similar. Could anybody help me out? I wanted to get a Corsair Professional Series Gold PSU, but was unsure which wattage I'd need. Honestly wish they had something in between 850w & 1200w.... but looks like I'm going to have to choose between the two.

My build is a WIP (when is it not?) right now, so I don't have everything yet, but here's what I'm planning on going with.

Custom watercool loop with a MCP655 pump going through CPU and both GPU's.
-i5 2500k OC'd to 4.6-4.8 using a small voltage bump
-ASRock Z68 Extreme3 Gen3
-Two 7950's in Xfire, both OC'd to 1.15Ghz and a small voltage bump (using this:http://www.guru3d.com/article/radeon-hd-7950-overclock-guide/3)
-4x4GB DDR3 @1600 w/ no voltage increase
-Plextor M3 Series 128GB SATA III & Plextor M3 Pro Series 256GB SATA III
-600GB WD 7200RPM HDD
-Small Phobya LED kit, may change to cold cathodes
-Possibly a sound card in the future
-Basic CD/DVD optical drive
-3 180mm AP Fans that come in the Raven RV02-E
-1 x 120mm for the top, and possibly 1-2 more fans if I decide to add a second radiator when I watercool.

I was thinking that the 850w PSU would be fine for this, but I wanted to make sure before I dropped a couple hundreds dollars. I don't want to be borderline pushing it either, I want to always be under 775w or so @ 100% load.

 

[GI_JONES]

7950's in crossfire require about 700 watts, but considering the overclock, additional fans,lights, etc, you need a bit more. I would think the 850 is plenty. Here is another guide for power usage: http://www.realhardtechx.com/index_archivos/Page362.htm

 

[Devastater6194]

850 should be fine. Plus the AX850 is one of the best out there and take over 900 I've read so it'll be perfectly fine for you.

 

[RetiredChief]

First off, I never use the calculators. What I do do is google a review of the GPU setup and look at system Power.

Here is what I found - NOTE it is for a 7970 Xfire, so yours will be little less, but then you throw in Your OC:
Quote
Our test system is based on a power hungry Core i7 965 / X58 system. This setup is overclocked to 3.75 GHz. Next to that we have energy saving functions disabled for this motherboard and processor (to ensure consistent benchmark results). On average we are using roughly 50 to 100 Watts more than a standard PC due to higher CPU clock settings, water-cooling, additional cold cathode lights etc.

We'll be calculating the GPU power consumption here, not the total PC power consumption.

Measured power consumption for two cards in Crossfire

System in IDLE = 166W
System Wattage with GPU in FULL Stress = 567W
Difference (GPU load) = 401W
Add average IDLE wattage ~6W
Subjective obtained GPU power consumption = ~ 407 Watts
End Quote
Added : and the Ref: http://www.guru3d.com/article/radeon-hd-7970-crossfire-review/7

Bottom line a Corsair TX750 would be an excellent choice.

 

[GI_JONES]

It seems as though most of the calculators are fairly conservative, or using worst case scenario almost. This makes sense since they are unsure about the actual quality and efficiency of the psu in question. With a top notch unit I wouldnt be suprised if you could actually get away with 650 watts, but you also have to factor in loss of efficiency with age, and the fact that you probably dont want to be stressing the unit by having it run full tilt all the time. That being said a quality 750-850 watt unit should provide plenty of juice with some to spare.

 

[ilysaml]

Bottom line a Corsair TX750 would be an excellent choice.

Exactly, you could have just included that

 

[Guest]

Damn so would the AX750 be enough? Even if the 2500k is OC'd w/ voltage tweak as well as the 7950's? Because it's currently $145 + $20 MIR.... I want to have quite a bit of overhead room, and not always have my PSU on 90-100% load=\

 

[ilysaml]

If you OC each nail in your PC, a 700W PSU is very sufficient. Go for it.

 

[ko888]

For a system using two AMD reference design Radeon HD 7950 graphics cards in 2-way CrossFire mode AMD specifies a minimum of a 700 Watt or greater power supply. The power supply should also have a combined +12 Volt continuous current rating of 45 Amps or greater and have at least four 6-pin PCI Express supplementary power connectors.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important factor.

Overclocking of the CPU and GPUs will require an additional 17 Amp increase to the combined +12 Volt continuous current ratings, recommended above, to meet the increase in power required for the overclock. The additional amount required is based on the magnitude of the overclock you are trying to achieve.

The Corsair Professional Series Gold AX750 (CMPSU-750AX), with its combined +12 Volt continuous current rating of 62 Amps and with four (6+2)-pin PCI Express supplementary power connectors, is sufficient to power your system configuration with two manually overclocked Radeon HD 7950 graphics cards in 2-way CrossFire mode and with the i5-2500K overclocked to 4.8 GHz.

 

[ilysaml]

@ko888
You can always quote guru3d recommendation instead of taking the time to bold words. Also, you could have just said your opinion simply without blinding my eye with the green font.

 

[ko888]

@ko888
You can always quote guru3d recommendation instead of taking the time to bold words. Also, you could have just said your opinion simply without blinding my eye with the green font.

I'm not naive enough to assume that people don't run Furmark.

Guru3D, in the past, use to provide maximum power consumption figures based on Furmark but not anymore.

In their power supply recommendation for the Radeon HD 7950 in 2-way CFX they don't even specify the PSU's +12 Volt continuous current rating required. They also don't specify how much more power the graphics cards consume when they are manually overclocked above the reference clocks that they use in their test.

 

[ilysaml]

Well, and no one runs Furmark for 24/24 hours. And no one puts his GPU in a full workload 24/24. So the situation is a bit different.

Their Perspective and they seem to be right about it;

there has been a lot of discussion using FurMark as stress test to measure power load. Furmark is so malicious on the GPU that it does not represent an objective power draw compared to really hefty gaming. If we take a very-harsh-on-the-GPU gaming title, then measure power consumption and then compare the very same with Furmark, the power consumption can be 50 to 100W higher on a high-end graphics card solely because of FurMark.

We decided to move away from Furmark in early 2011 and are now using a game like application which stresses the GPU 100% yet is much more representable of power consumption and heat levels coming from the GPU. We however are not disclosing what application that is as we do not want AMD/ATI/NVIDIA to "optimize & monitor" our stress test whatsoever, for our objective reasons of course.

BTW, I didn't mean any sarcasm.

 

[ko888]

Well, and no one runs Furmark for 24/24 hours. And no one puts his GPU in a full workload 24/24. So the situation is a bit different.

Their Perspective and they seem to be right about it;

there has been a lot of discussion using FurMark as stress test to measure power load. Furmark is so malicious on the GPU that it does not represent an objective power draw compared to really hefty gaming. If we take a very-harsh-on-the-GPU gaming title, then measure power consumption and then compare the very same with Furmark, the power consumption can be 50 to 100W higher on a high-end graphics card solely because of FurMark.

We decided to move away from Furmark in early 2011 and are now using a game like application which stresses the GPU 100% yet is much more representable of power consumption and heat levels coming from the GPU. We however are not disclosing what application that is as we do not want AMD/ATI/NVIDIA to "optimize & monitor" our stress test whatsoever, for our objective reasons of course.

BTW, I didn't mean any sarcasm.

The problem is that when you don't take it into account and the user runs Furmark with a power supply based on their recommendation the power supply may trigger its OCP and shut down and the user is then left wondering what the heck happened.

I would rather have a power supply that can handle it rather than one that can't.

 

[ilysaml]

The problem is that when you don't take it into account and the user runs Furmark with a power supply based on their recommendation the power supply may trigger its OCP and shut down and the user is then left wondering what the heck happened.

I would rather have a power supply that can handle it rather than one that can't.

You are true about this.

 

[RetiredChief]

AS I said a Corsair 750 would be an excellent choice. More headroom then go to the 850.

ilysaml - I had seen that chart, but it only provided GPU power and I was looking more toward total system power.

ko888 - Glad you brought that up about furmark. Should be OK as you should always go 100+ over the Nominal wattage. Which should be enough headroom. Personnally I think they should have stuck with furmark and emphasized normal user would be under this. Furmark is used by many to both benchmark and stress test their "High" end GPU

 

[Guest]

Alright, I appreciate everybody's input, now I believe it's just a matter of deciding if I want to spend an extra $40 or so for that worry-free headroom. I always like to have extra room to extend on.

 

[Guest]

Best answer selected by kllrfrk.