GTX 275 in SLI power requirements?

[ganzey]

Iv just found this http://www.hardwarecanucks.com/foru...0-nvidia-geforce-gtx-275-896mb-review-20.html

They measured the consumption using an inline meter , for some reason the 275 pulls more juice than most

Watts / volts = amps 345 watts Devided by 12 = 28.8 amps!

What the hell was i thinking buying two of these I had no idea what i was letting myself in for
so now im needing dam near 60 amps just to run the cards

what about the Cpu how much will a crosshair 2 , With an overclocked 965 quad core pull???

that power usage is for the entire system . so i think a 965 OC would take around 12-13 amps UNDER LOAD.

 

[mimic58]

that power usage is for the entire system . so i think a 965 OC would take around 12-13 amps UNDER LOAD.

Ah yes i see , i just looked at the 345 watts an thought Sh*T but i see now its only adding a hundred or so watts

Sweet So that Beefcake they have on Scan website should easily be able to handle the two cards cpu m/b and the 4 way raid i was planning this is excellent news , Just wish i didnt have to go 3 days on this stock pc till new psu arrives , No games ARggg

 

[jevery]

Here's what I'm running with a Corsair 850HX, a pair of 4870s, a Q9650 (OC'd), 7 case fans, a 4 drive RAID, 2 DVD burners, a floppy drive, and a couple of cold cathodes.

I ran this setup successfully for over a year with a 4 rail 700 W Silverstone PSU. though, one day my RAID went down and I determined that I had overloaded a rail. I'll be sticking with single rail PSUs from now on. I think the 700 was marginal for everything that I eventually stuffed in the case. Give yourself some room to grow and get the 850, or the 1000 and you should be good for the next build too.

 

[Computer_Freak]

is there any single card that can completely max crysis out? i mean completely max it out?

im running Crysis with a GTX295 @

1440 x 900,
Ultra High settings (did the tweak that unlocks Ultra High for XP)
4 x AA,
16 x AF,
shaders etc (in windows) set to highest quality

i get an average of 40fps...

the game is highly playable

but sometimes i get some lag and my frames drop


My card needs a recomended 650W PSU. Im running a E6400 OCed to 3.0GHz, GTX295, 2HDD, DVD writer, 8 fans, with a 750W corsair... Im sure i can maybe push 2 x GTX295 on my system (that will be seriously pushing it though)

Remember, nvidia recomends more than needed, that so people dont mess anything up. There was a guy here running a full system, with 2 8800GTS 512 on a 520W Corsair...

Trust me, a 850W (especially since its single rail) is plenty

They measured the consumption using an inline meter , for some reason the 275 pulls more juice than most

Watts / volts = amps 345 watts Devided by 12 = 28.8 amps!

thats the power consuption of the whole system under load.

so you will be fine with a 850W PSU. Hell a 750W will even suffice

 

[Okedokey]

To the OP, please post the model of PSU you intend to buy prior to buying.

The two cards in SLI with standard clocks will draw no more than 440W. That is 36A. Just for the cards.

If you plan to overclock them or run them above 25oC ambient you risk drawing more current than that.

A TX750W Corsair has 60A on a single 12V rail. This is sufficient for that system. Anything less though is risking it.

http://www.newegg.com/product/product.aspx?item=n82e16817139006

 

[NCspecV81]

any reputable 750w psu will work for sli 275's. The corsair 850 would be overkill imho. However, it's always nice to have a little extra psu than needed.

 

[The Chad]

Found on Club 3D's info page for the GTX275:

• Minimum 550Watt or greater system power supply (with a minimum 12V current rating of 40A)

• 800Watt or greater power supply for SLI™

http://www.club-3d.com/products/products_ending_page_7_with_id.cfm?product_id=131

 

[Okedokey]

Wattage doesn't mean a great deal. There are plenty of higher wattage garbage units out there.

 

[Christian Darrall]

i'm sure if you buy a 1000w power supply it will have enough juice to run SLI and all the extra you may want to add in the future,

i cute have a nice SLI compatible PSU for under £100.00

 

[mimic58]

Wattage doesn't mean a great deal. There are plenty of higher wattage garbage units out there.

yeh i totally agree with this guy , iv looked at stacks of powersupplys since my 800 blew up , And 80% of them have multiple rails at arround 20 amps regardless of wattage the thing you want to be looking at is the 12v rail

I'v opted to go for a single rail 80 amp and im confident i will now have enough juice to run the two cards mb and raid without any risk of overloading one of the rails

The other problem with multiple rail is you have no easy way of identifying which connectors are on which rails you could easy put to much onto one rail and not get the ballancing right

 

[Computer_Freak]

• Minimum 550Watt or greater system power supply (with a minimum 12V current rating of 40A)

• 800Watt or greater power supply for SLI™

see, that just proves that nVidia overcompensates, and takes into consideration bad quality PSU's.

a full GTX275 rig uses about 380W on load...

thats nearly 200 less than recommended...

800W is overkill, but nice to have, for future expansion, and so that the PSU doesnt run at max all the time.

 

[mimic58]

see, that just proves that nVidia overcompensates, and takes into consideration bad quality PSU's.

a full GTX275 rig uses about 380W on load...

thats nearly 200 less than recommended...

800W is overkill, but nice to have, for future expansion, and so that the PSU doesnt run at max all the time.

As already said wattage is not the issue its avialable current on the 12v rails and ability to distrubute the load

 

[Okedokey]

Look it comes back to quality and the PSU's ability to provide stable 12V current without overheating etc. etc.

nVidia requires a 550W PSU with 40A on it. Well fine, however most people new to the mainstream PC PSU market make 1 or more of the following mistakes:

• they believe that a PSU claiming to have multiple rails will. Almost all of these PSUs actually only split the ONE 12V rail into several via voltage divders (electronics) rather than seperate physical windings on a transformer.
• Wattage is important - its not directly important - amperage is (on the 12V rail)
• add up the total 12V rail manufacturer stated amperage as a total avialble current on the 12V rail. You cannot do this UNLESS it has EPS12 certification.

Here is an example of where wattage alone is very misleading:

550W Antec - 19A on the 12V rail available (ATX design limitations / no EPS)
550W Corsair - 41A on the 12V rail available (EPS)

Same wattage, different amperage. Only one PSU (the Corsair) is able to run this setup. So in this example you can see that there is absolutely no comparison that can be made between the PSUs. More importantly there is no assessment that can be made based on the 550W minimum criteria alone. Wattage means little.

Finally, don't purchase a PSU with 'just enough' power for your current system. You may decide in 2 months to want watercooling or lights, or to overclock etc etc. Go for a PSU with around 60A for expansion ability. The HXCorsair is only $130 with a 7 year warranty, 90% efficiency (find that elsewhere), 60A on the 12V rail. http://www.newegg.com/Product/Product.aspx?Item=N82E16817139010&Tpk=corsair 750Hx

Perfect buy in this situation i reckon.

 

[Computer_Freak]

As already said wattage is not the issue its avialable current on the 12v rails and ability to distrubute the load

thats why i said they overcompensate for bad PSU's

as Bigfella pointed out, it might have the same wattage, but much less current can be delivered. Thast what i meant they were overcompensating for

It is mostly the amps that is important, but the watts on the 12v rail usually depicts what the amps will be...

 

[mimic58]

thats why i said they overcompensate for bad PSU's

as Bigfella pointed out, it might have the same wattage, but much less current can be delivered. Thast what i meant they were overcompensating for

It is mostly the amps that is important, but the watts on the 12v rail usually depicts what the amps will be...

Yeh i think your right , Their trying to cover themselfs for cheap hardware and rightfully so, I used a cheap 800w supply and it didnt last 5 minutes

 

[meticadpa]

You can easily run SLi GTX 275s on a 750W power supply of decent quality.

You could probably use something like the Antec TruePower New 650W, but your power supply's life and efficiency may be lower than usual, as a result of the high load percentage.

thats why i said they overcompensate for bad PSU's

as Bigfella pointed out, it might have the same wattage, but much less current can be delivered. Thast what i meant they were overcompensating for

It is mostly the amps that is important, but the watts on the 12v rail usually depicts what the amps will be...

Wattage ALWAYS = Amperage * Voltage. So if you've got 50A on the 12V rail, you do 50 * 12, to get 600W.

For multi-rail power supplies, you don't just add the rails together, but usually there's something that says "Don't get 12V load exceed 500W" for example, so you'd divide the figure that it states (in this case, 500W) by 12.

 

[mimic58]

You can easily run SLi GTX 275s on a 750W power supply of decent quality.

You could probably use something like the Antec TruePower New 650W, but your power supply's life and efficiency may be lower than usual, as a result of the high load percentage.



Wattage ALWAYS = Amperage * Voltage. So if you've got 50A on the 12V rail, you do 50 * 12, to get 600W.

For multi-rail power supplies, you don't just add the rails together, but usually there's something that says "Don't get 12V load exceed 500W" for example, so you'd divide the figure that it states (in this case, 500W) by 12.

Yes but at what duty cycle can it maintain that current???
And how is your very basic ohms law calc factoring the diversity of the system and how the current is split, Your wattage may equate to 50amps but it maybe split over 5 rails at 10amps a rail with a duty cycle arround 80% meaning it can only deliver this full current for short periods (peak power)
Now you have a situation where any one rail cannot provide enough current to run the item so the rails have to be parralleled up together, Now because it is dam near imposible on most cheap supplys to actualy see which power connectors are connected to which rails , how can you garantee you have not connected a device to one single rail instead of say two

You cant apply the Watts devided by volts = amps calculation here it just wont work unless its a Single rail supply and the duty cycle is 100%, |There is also the question of efficeincy , The ohms law calculation you have applied assumes a 100% efficiency in the power supply mean it converts 100% of the watts to amps, NO psu can ever offer this some watts are always lost to heat
on avarage expect about 90% efficiency at best

 

[Okedokey]

mimic, ill agree meticadpa is possibly using Year 10 physics as gospel, however what you are referring to relates to ATX design standard PSUs without EPS12. In this case, meticadpa is right, the Antec true power has EPS12 certification so it can supply the nominal rail amperage as a total.

 

[mimic58]

mimic, ill agree meticadpa is using Year 10 physics as gospel, however what you are referring to relates to ATX design standard PSUs without EPS12. In this case, meticadpa is right, the Antec true power has EPS12 certification so it can supply the nominal rail amperage as a total.

what is the difference ?? The only referencess i can seem to find to EPS12 simply regard to the type of connectors and say nothing about duty cycle rail layout or deisgn differences from atx.. Obviously you know something i dont , Any chance you could explain?


""pure guess, I'm assuming it allows it to channel all of its current to one output if needed?""

 

[Okedokey]

what is the difference ?? The only referencess i can seem to find to EPS12 simply regard to the type of connectors and say nothing about duty cycle rail layout or deisgn differences from atx.. Obviously you know something i dont , Any chance you could explain?


""pure guess, I'm assuming it allows it to channel all of its current to one output if needed?""

Have you read it? Pure guess, I bet you haven't.

The latest EPS standard refers to:

* Removal to references to common and split 12V planes (ie you can add the 12V rails)
* Added cross loading plots (i.e you can add the 12V rails)
* Increase 12V rail currents (over and above 240VAC safety limits on ATX PSUs)

btw, efficiency issues will simply mean it will draw more amps from the wall to deliver the intended power - it doesn't work how you have described, and duty cycle is expressed practically in MTBF ratings, at least 40oC. So really, with a 7 year warranty, who gives a shit.

*edit* oo i can hear google being hit hard now