What PSU

stulid · 27 Sep 2011 at 19:24

Even Guru3d say a good a 650W PSU is needed for crossfire 6950's, and they use a older socket 1366 based test system which uses more poer than Sandybridge.

max51 said:
650watt is not enough and even a 750watt is cutting it fine. The power draw on my system is over 700watts and that is with only a small overclock.

And as Surveyor says, that works out to around 650W from the PSU

C64 · 27 Sep 2011 at 19:38

Isn't the point though that why push the psu to it's limits or close to ? better to have a psu running at 50-70% load meaning less heat and noise and wear.Whichever you decide make sure to get one with a 7 year warranty.

max51 · 27 Sep 2011 at 19:56

stulid said:
Even Guru3d say a good a 650W PSU is needed for crossfire 6950's, and they use a older socket 1366 based test system which uses more poer than Sandybridge.

And as Surveyor says, that works out to around 650W from the PSU

My calculations must differ from yours. Two GPU's not overclocked out of the box SLI or Crossfire in game eg Crysis, BFBC, pulling around 500w + a CPU at 125w. That is 625w.
Question. What about power draw from Motherboard, RAM, Fans and DVD/ BLU RAY drives and HDD, not incl any overclocking.
650w is a bare mimimum.
I always understood it is better to have more than you need as it does not put under as much stress. Please corect me if i am wrong

stulid · 27 Sep 2011 at 20:05

A 6950 2Gb pulls 182W max, 109W average - http://www.techpowerup.com/reviews/HIS/Radeon_HD_6950/27.html

A i5 2500K has a much lower TDP at 95W

It all adds up to a i5 2500K system with Crossfire 6950 using less power than you think. You use "calculations", I use results gained from websites testing with real equipment.

All these "PSU calculators" you find at PSU manufacturer websites are well of the mark, probably trying to get someone to spend more money.

RJC · 27 Sep 2011 at 20:11

Been using a plug in power monitor on my system and got the following results:

Idle (watercooled) 199w
CPU Load (Prime) 335w
GPU Load (Furmark) 390w
Prime & Furmark: 510w

I have also used Crossfire 5850 which pulled 430w from the mains and 480 GTX which I managed to get 615w.

max51 · 27 Sep 2011 at 20:23

stulid said:
A 6950 2Gb pulls 182W max, 109W average - http://www.techpowerup.com/reviews/HIS/Radeon_HD_6950/27.html

A i5 2500K has a much lower TDP at 95W

It all adds up to a i5 2500K system with Crossfire 6950 using less power than you think. You use "calculations", I use results gained from websites testing with real equipment.

All these "PSU calculators" you find at PSU manufacturer websites are well of the mark, probably trying to get someone to spend more money.

I do not use those calculators as they all differ and can be quite a bit out at times . I use power draw on each indavidual componant maxed and idle then calculate what i will need from there.
Would you rather push a PSU at 90% or even a 100% with the chance it might be ok or it might start causing problems or have one that will last the life of the system and any future upgrades.
And also take into account that PSU's degrade over time.

stulid · 27 Sep 2011 at 20:28

max51 said:
I do not use those calculators as they all differ and can be quite a bit out at times . I use power draw on each indavidual componant maxed and idle then calculate what i will need from there.
Would you rather push a PSU at 90% or even a 100% with the chance it might be ok or it might start causing problems or have one that will last the life of the system and any future upgrades.

It wont be at 90% or 100%

And where did you get 500W for two cards from? this is more than the PCi specifications allow, 75W per 6pin connector and I think its 75w (might be 50W but cant remember) from a 16X PCi-E slot. So thats a max of 225W each, or 450W for a pair of 6950 cards, but they dont draw that much as shown.

And also take into account that PSU's degrade over time.

The OP is after a brand new PSU.

olivier renault · 27 Sep 2011 at 20:35

max51 said:
I do not use those calculators as they all differ and can be quite a bit out at times . I use power draw on each indavidual componant maxed and idle then calculate what i will need from there.
Would you rather push a PSU at 90% or even a 100% with the chance it might be ok or it might start causing problems or have one that will last the life of the system and any future upgrades.
And also take into account that PSU's degrade over time.

sooo that's 700W 'theoretical'? Should really use a plug in monitor.

max51 · 27 Sep 2011 at 20:44

stulid said:
It wont be at 90% or 100%

And where did you get 500W for two cards from? this is more than the PCi specifications allow, 75W per 6pin connector and I think its 75w (might be 50W but cant remember) from a 16X PCi-E slot. So thats a max of 225W each, or 450W for a pair of 6950 cards, but they dont draw that much as shown.

The OP is after a brand new PSU.

the same place you got your CPU example from Anand Tech.
Also even with your calculations, GPU,CPU and all ancileries. I will let you work it out.
not much headroom to play with there.

stulid · 27 Sep 2011 at 20:47

max51 said:
the same place you got your CPU example from Anand Tech.

That would be the TOTAL SYSTEM USAGE including cpu/ram/board for the Anandtech test system.

Not just the pair of cards

stulid · 27 Sep 2011 at 20:55

And just to show I am not lying

http://www.anandtech.com/show/4061/amds-radeon-hd-6970-radeon-hd-6950/24

Cysis - 470W
FurmarK - 509W

The top of the graphs say "Total System Power Consumption"

The test system used is - http://www.anandtech.com/show/4061/amds-radeon-hd-6970-radeon-hd-6950/12

CPU: Intel Core i7-920 @ 3.33GHz
Motherboard: Asus Rampage II Extreme
Chipset Drivers: Intel 9.1.1.1015 (Intel)
Hard Disk: OCZ Summit (120GB)
Memory: Patriot Viper DDR3-1333 3 x 2GB (7-7-7-20)

Geeman1979 · 27 Sep 2011 at 21:15

stulid said:
And just to show I am not lying

http://www.anandtech.com/show/4061/amds-radeon-hd-6970-radeon-hd-6950/24

Cysis - 470W
FurmarK - 509W

The top of the graphs say "Total System Power Consumption"

The test system used is - http://www.anandtech.com/show/4061/amds-radeon-hd-6970-radeon-hd-6950/12

So what PSU,s would you reccomend to power a couple of 5850s xfire 2600k overclocked,couple of HDs,Sound card,DvD Writer and the usual case fans! around the £80 ish mark?

RJC · 27 Sep 2011 at 21:17

http://www.overclockers.co.uk/showproduct.php?prodid=CA-117-AN&groupid=701&catid=123&subcat=1088

http://www.overclockers.co.uk/showproduct.php?prodid=CA-006-LA&groupid=701&catid=123&subcat=2057

Couple of options above

Geeman1979 · 27 Sep 2011 at 21:21

I suppose the Lepa would be worth the extra tenner! for the higher wattage.

max51 · 27 Sep 2011 at 21:23

At the end of the day it boils down to one thing and one thing only, personal choice.
We could keep on bouncing this between us all night and get nowhere, i have my way and you have yours and they both work for us. In all the years i have worked with and around computers i have never had a cooked PSU due to a bad PSU chioce.
So lets leave it there and for the op to make his choice and hope we have helped and not confused. All of us on here try our best to help with good advice, but we all have our own ways and opinions.

PeterNem · 27 Sep 2011 at 21:44

max51 said:
At the end of the day it boils down to one thing and one thing only, personal choice.

Yes, I'd want to draw a line under it too had I missed the really blatantly obvious label on those graphs ""Total System Power Consumption" or misunderstood what was possible and within spec for the PCI-E interface in terms of power delivery.

A decent 650 watt PSU won't leave too much room to spare but should be fine.

ooEy · 27 Sep 2011 at 22:12

ooEy said:
The Antec New Truepower is a good PSU but im not sure its suitable for CF.

Mine has become redundant as it wont run 2 x 5850s with a few HDDs and Fans,

RJC · 27 Sep 2011 at 22:17

Must be something wrong, as crossfire 5850 on my system in sig with water-cooled cpu and several hard drives pulled 430w from the mains with Prime & 3D Win mark running together.

ooEy · 27 Sep 2011 at 22:23

That is strange, My spec ....

[email protected]
2x2GB 1066 DDR2
2 x 1TB HDD
2x 500GB HDD
1 x 60GB SSD
Corsair H50
X-Fi
5 x 120mm Fans
2 x 140mm Fans

Is running atm with only the SSD installed, but as soon as I add any more HDDs the PC will turn off after about 10 Mins of BC2. I know its the PSU as it runs fine for hours with all HDDS if I run another PSU externally just for the 2nd card.

As I said in a previous post, I have a new PSU enroute Antec HCG 900w.

You think the 650w maybe faulty ?

* Sorry for the hijack

RJC · 27 Sep 2011 at 22:26

Must something screwy with it, as I would suspect you would pull a little less than mine did!

The Antec 650w would / should have handled your system without issue.