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PSU for 7950's

Dougiebabe2003

Dougiebabe2003

Dougiebabe2003

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Joined
31 Oct 2005
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746
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Hi,

Looking to get 2 or maybe 3 7950's in one rig and want to know the minimum PSU wattage and amps that I should be looking at.

Will want to run them overclocked and over-volted, so from the info I have found I will need about 225 watts per card + system power.

For 2 cards would 550-600w be enough and for 3 would a 750w be enough or should I be looking for more?

Many thanks in advance,

Doug
 
Dougiebabe2003 said:
Hi,

Looking to get 2 or maybe 3 7950's in one rig and want to know the minimum PSU wattage and amps that I should be looking at.

Will want to run them overclocked and over-volted, so from the info I have found I will need about 225 watts per card + system power.

For 2 cards would 550-600w be enough and for 3 would a 750w be enough or should I be looking for more?

Many thanks in advance,

Doug
Click to expand...


What about the rest of your rig?

That can use anything up towards 200w

Do you plan to overclock

All the above can make a big difference.
 
I'm running 2 7950's happily on a Corsair 750w.

I also have an i7 875k with Ht enabled at 4.2 ghz, 8gb Ram 2000mhz, Corsair H50, 2x 120gb SSD's, 2x 500gb Momentus XT's, 1x 2tb WD Green, 6x 120mm fans, 1x 140mm fan, 1x BR Drive, 8x USB devices and a partridge in a pear tree.
 
whyscotty said:
What about the rest of your rig?

That can use anything up towards 200w

Do you plan to overclock

All the above can make a big difference.
Click to expand...

Rest of the rig will never be over-clocked and will relativity low power but would like a bit of headroom.

It's going to be a mining rig so the main power consumption will be the gfx cards will be the main power users.
 
Columbo said:
I'm running 2 7950's happily on a Corsair 750w.

I also have an i7 875k with Ht enabled at 4.2 ghz, 8gb Ram 2000mhz, Corsair H50, 2x 120gb SSD's, 2x 500gb Momentus XT's, 1x 2tb WD Green, 6x 120mm fans, 1x 140mm fan, 1x BR Drive, 8x USB devices and a partridge in a pear tree.
Click to expand...

This is what makes me wonder if I might get away with 3 on a 750w, I'm thinking of going AMD Sempron single or dual with only 1 HDD for the 'System', the rest will be the cards
 
Dougiebabe2003 said:
This is what makes me wonder if I might get away with 3 on a 750w, I'm thinking of going AMD Sempron single or dual with only 1 HDD for the 'System', the rest will be the cards
Click to expand...

Not sure if serious but I'll bite....

I doubt a Sempron will keep up with 1x 7950 so tri-Fire would be an utterly pointless exercise.
Its a chip designed for word documents and pdf files not for crunching huge amounts of gaming data.

At minimum you should be looking at a bottom spec Piledriver chip or Intel i5.
 
I'm running 7950 Crossfire on a 630w PSU.

My PC pulls 550w from the wall so at 80% efficiency my PC only actually uses around 440w so I have ~200w left in reserve.
 
Columbo - I am serious, from what I can tell there isn't a massive load on the CPU when it's feeding the gfx card for mining... I could very well be wrong. Just to re-iterate though, it will not be used for gaming and only for mining and all that mining will be done on the cards, not the CPU.

Almighty - So you have 2 7950's on a 630w and all seems well then? Have you overclocked the GPUS at all? any voltage mods?

I'm thinking now maybe 600-650w might be ok for xfire but 750w preferred and 800-850w for tri-fire with 1000w preferred.

Many thanks to all.
 
I already tested TriFire 7950s running at 1000/1375 and an I7 [email protected] and from the wall was drawing 780W tops... so this would be around 620W from the PSU.

But the gpus were at 95% load max, maybe bootlenecked by the CPU.
 
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I see you seem to be thinking what's the minimum I can get away with, which will work with a top quality PSU but just keep in mind a couple years down the line you might wish you got a bit more in the long run. But yes 750w will be enough for crossfire and 850-900 should make it for tri-fire.
 
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Drangueos said:
I already tested TriFire 7950s running at 1000/1375 and an I7 [email protected] and from the wall was drawing 880W tops... so this would be around 700W from the PSU.

But the gpus were at 95% load max, maybe bootlenecked by the CPU.
Click to expand...

Your PSU must be very inefficient, I'm only pulling 550w from the wall with 3x 7950's at higher clock then tested with.

So adding a third card equates to an extra 300w power draw? Something isn't right there.
 
Dougiebabe2003 said:
Columbo - I am serious, from what I can tell there isn't a massive load on the CPU when it's feeding the gfx card for mining... I could very well be wrong. Just to re-iterate though, it will not be used for gaming and only for mining and all that mining will be done on the cards, not the CPU.

Almighty - So you have 2 7950's on a 630w and all seems well then? Have you overclocked the GPUS at all? any voltage mods?

I'm thinking now maybe 600-650w might be ok for xfire but 750w preferred and 800-850w for tri-fire with 1000w preferred.

Many thanks to all.
Click to expand...

Ah fair enough, I have no idea about all this bitcoin business so I'm sure you are correct.
 
almighty15 said:
Your PSU must be very inefficient, I'm only pulling 550w from the wall with 3x 7950's at higher clock then tested with.

So adding a third card equates to an extra 300w power draw? Something isn't right there.
Click to expand...

Indeed.

According to my smart meter, my PC at 100% load pulls 406W though I've not seen anywhere near that in actual gaming.

Farcry 3 seems to be the game pulls the most for some reason at 360w. I've no idea why :confused:
 
Just been through this and ended up buying an XFX Pro Core 750w.

I had hoped to make do with the Antec Truepower 650 but found that , sadly, one of the pci-e cables would not fit the gpu :( and it was therefore unuseable.(it does seem that it is difficult to buy just a cable)

What I had read had indicated that the 650 should be enough but as there would be little if any headroom left and as I do , and intend to continue, overclocking my cpu etc I decided to give my 650 to my son and buy the 750.

Although the 750 is not modular it is , I believe, made by seasonic , is a good quality psu, 5 yr warranty and at a very reasonable price :) , it made sense to me.

Might be a little ott but it gives room to grow etc :) (Would mention that I plugged in the wattage tester/gauge after installing (as one does - sad eh') and noticed that at one point a reading of 695 w - I do appreciate that this would probably have not been a problem for the 650 psu but....)

Would go for a 750 at least - the Be Quiet 850 on offer this week is very tempting :D
 
almighty15 said:
Your PSU must be very inefficient, I'm only pulling 550w from the wall with 3x 7950's at higher clock then tested with.

So adding a third card equates to an extra 300w power draw? Something isn't right there.
Click to expand...

I have a Corsair TX850, that should be 80%, the power draw was 780W, (880w was a typo, it was 3am so forgive me :D) test was running CPU + GPU stress test, to load everything at 100% to check my peak power draw

Now running 2x 7950@1100/1375 while doing only GPU benchmarks it tops at 600W, just tested, how can you pull 550W from the wall with 3x 7950?

Also I have 3HDs, 3SSDs, Fan controler, 12 fans...
 
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