How many amps per card?

[Karribu]

Hi,
iv'e been having trouble with my sli rig...

AMD 64 Athlon 4000+
8AN Sli Premium Motherboard
2 gig memory
2 x Gainward 512mb special edition 7900 GTX PCX SLI
psu is X-power 700 watt SLi compatable
2 x 200 GB Maxtor HDD

First off i couldnt get sli to work properly, i think i might have now (driver issues, i had to install the driver twice, once for each card) then when in sli mode and in a fairly high res and any slight anti alias mode and the comp switched off completely. I think the power supply can't put out enough amps continually to the cards, im not sure.

So if you agree, do you think i should get a new well known PSU instead of the one i have that no one seems to have heard of. Or do i get this thingy....

http://www.overclock3d.net/reviews.php?type=3&id=79&page=1&desc=fsp_booster_x3_300w_12v_psu

How many amps do you need for each card? i heard different numbers from different places, most seem to say 15 per card so 30 in total. Does that sound right? or is less needed?

Any help appreciated

Karri

 

[waylander]

Those graphics cards are very power hungry but a 700w psu should be more than enough for them. Can you tell us what it says in the psu in terms of the number of amps for each 12v rail? There are 3 12v rails I believe.

 

[Karribu]

Thanks for reply!

Yeah sure, i'll post tomorrow, i have to get everything out the case to find out and its getting late here.

Basically It came with the case but I can't find any info on it on the net at all. There's 1 lead that runs into both cards. Any game will work in high res from 1 second to 30 seconds then it shuts down. At first i thought it was maybey a card being faulty but then i found this....

http://www.extremetech.com/article2/0,1697,1932947,00.asp

sounds just like my problem.

Anyway I try and find the info for ya, you would have thought it would have been supplyed on the packaginf but it isnt. 8O

 

[Karribu]

ok its an ATX-700w and has 4 12+ rails.

on each rail it says 16amps.

I would have thought this was enough, but like that link says, a lot of psu can put out the correct amps, just not continually.

Im really confused at what to do.

 

[pengwin]

that doesnt look like a bad PSU. it has a decent price and a good amount of Amp's


i think u should get the X3 thing.

cheaper and u can reuse it when ur PSU dies, or if u decide to build a conroe rig.

 

[waylander]

I don't really know the maker "x-power" so I can't say anything on the reliability. It will be cheaper to get that 300w gpu psu than to get a new 700w psu from a good maker though.

 

[Karribu]

Yeah, the blue leds are enough to make me wanna buy it 8O

But there's 1 question before i click the order button. Will it give enough amps to support 2 x 9700 GTX PCX 512mb?

 

[NaDa]

I think everyone is overexagerating about the power requirements.

I have been doing some measuring. I have connected an ampermeter to the power cable that goes into the PSU.
I have and Athlon64 3500 (Newcastle), X800XT, 2x512DDR, 2x200GB HDD, DVD-RW and a lot of fans.

Under load in games the PC was maxed to about 0.8 Amps if you put the 220V into the equation you get about 180W. I have a 500W PSU (25A 12V rail).

So you can asume that the CPU or the graphic card dont pull more than 100W (probably about 80W).

So you have a CPU and 2xGPU == 300W + some other stuff == 350W top!

People say that modern computers mostly use the 12V rail so my PSU can give me 12V*25A = 300W on the 12V rail. It alone is enought to power the whole thing.

Your has 4 x 12V*16A == 768W on the 12V rail. I think thats enough to power 2x your computer.

I think your CPU pulls probably 10% more power if it's a Newcastle or if it's a Venice than probably less. The 7900GTX is I think comparable to X800XT maybe 10%, 20% more (at best).

15Amps per card. That would be 15A*12V = 180W, no way! Probably around 7-9 Amps.

 

[waylander]

You are both right and wrong.

First of all if you OC then power requirements shoot through the roof. If you read toms article on the D805 then you'll notice that when it was overclocked to 4.0ghz that it used 225w of power BY ITSELF!

The 7900GTX is more like the 1900XTX (the 1800XT is like the 7800GT) and probably does pull 80w and if you sli then it does approach 160w.

So if you OC your processor AND OC your video cards (in SLI) then you could be needing 400W just for those 3 components.

On the other hand a standard machine with no OC and a 7800gt won't stress a 400w psu regardless of how many hdd's, fans, lights, optical drives and pci cards it has.

REAL life case is my system with the pump pulling 24w and 8 case fans (6 of them 120mm) and 4 cold cathode lights, OC my x2 4800+ to 2.8 and OC both my video cards to 500 / 1.4 and my Enermax 600w couldn't handle the load.

btw you can't just add the amps on the 4 rails together....

Further, most PSU's are tested for their power output at 25C whereas actual working environment in most computers is around 40C. My new Silverstone is rated at 750w at 50C. Low quality 400w to 600w psu's are rated those values at 25C and will drop 20% to 30% at 50C.

 

[pengwin]

I don't really know the maker "x-power" so I can't say anything on the reliability. It will be cheaper to get that 300w gpu psu than to get a new 700w psu from a good maker though.

its FSP waylander.

good company. i'd go with the X3

 

[Karribu]

Cheers guys but im stil not sure. I'd hate to buy another psu that can't cope.
Ai booster comes with my board. I tend to switch it off so there's no overclocking on the cpu (tbh i pushed it to 110% once and if anything the clock speed on the display lowered :? )

I don't know if the cards come pre-clocked, but i havent done any clocking to them. So if 12amps per card is enough i'll go with the X3. If however anyone thinks I need more, maybey 15 or 16 i'll save up and get an Antec psu or something, they seem to have good reviews.

 

[pengwin]

Cheers guys but im stil not sure. I'd hate to buy another psu that can't cope.
Ai booster comes with my board. I tend to switch it off so there's no overclocking on the cpu (tbh i pushed it to 110% once and if anything the clock speed on the display lowered :? )

I don't know if the cards come pre-clocked, but i havent done any clocking to them. So if 12amps per card is enough i'll go with the X3. If however anyone thinks I need more, maybey 15 or 16 i'll save up and get an Antec psu or something, they seem to have good reviews.

go witht he X3, its proven to support dual 7800GTX's

http://www.newegg.com/Product/Product.asp?Item=N82E16817104019

made by a very good company. FSP aka Fortron Source

 

[Karribu]

rgr that, on that link you posted it said 7900GTX too. yay!

 

[pengwin]

rgr that, on that link you posted it said 7900GTX too. yay!

yeah, i meant to say 7900GT, , u kno 8, 9 , next to each other. typo :\