3 7950's on a 850w PSU?

[grums]

Hi,

Im just wondering if it is possible to run 3 7950's or 7970's on a 850w PSU. The PSU is a 850w Be Quiet Dark Power Pro gold.

Im thinking about buying a 3rd GPU for my rig, but am unsure if the 850w will be able to handle 3 of them.

Any advice would be great.

Thanks.

[Go3Team]

I had 3 on a Corsair 850.  The temps were too high, but it did handle 3.

[grums]

I had 3 on a Corsair 850.  The temps were too high, but it did handle 3.

Thanks.

What about overclocking them. Will the PSU still hold up then? As I read overclocking increases watts.

[LostDutchman]

I had 3 on a Corsair 850.  The temps were too high, but it did handle 3.

Thanks.

What about overclocking them. Will the PSU still hold up then? As I read overclocking increases watts.

No.

If you have been running 3 cards on a 850 you have only been lucky that nothing has fried.  Don't worry.  Something will and soon and the more you overclock, the faster you will reach meltdown.

My $.02.

[PrintMule]

Does your 850 even have enough pci-e connectors?

Those molex 4pin=>6/8pin adapters tend to fry in such setups.

Edit: i see that it has

I've done 2x 7950 with crappy chinese no-name 500w, depends on your mobo and usage.

Gaming eats a lot more power than hashing.

[cdog]

Hi,

Im just wondering if it is possible to run 3 7950's or 7970's on a 850w PSU. The PSU is a 850w Be Quiet Dark Power Pro gold.

Im thinking about buying a 3rd GPU for my rig, but am unsure if the 850w will be able to handle 3 of them.

Any advice would be great.

Thanks.

It will work for a few weeks then your PSU will die, maybe if its platinum rated it will last a few months

[ineedit]

It could be near to the limit so get a wall watt meter and work out what load your 3 cards are using, if you have not under volted your cards you could be running into a problem.

I have 3 undervolted Gigabyte WF3's on a 850W M2 Cooler Master that pulls 735W at the wall, it is inside the spec of the PSU and will run for a long time.

[Raitzi]

Does your 850 even have enough pci-e connectors?
Gaming eats a lot more power than hashing.

Yes, but that is only because CPU power in gaming.

[pontiacg5]

In stock or optimal clock settings/volts, no. I highly doubt it. Especially not on that power supply, I've never heard of that brand.

Can it be done, yes. With some tweaking, undervolting, and possible underclock.

Should it be done? Probably not.

Can you just buy an extra 300-400W power supply for ~$20 and use it to run the new card? Or, use a cheap power supply to power the motherboard, then use all 850W to power the cards. I'd stay away from the 7970, still.

Don't use molex to pci-e power adapters!

[grums]

In stock or optimal clock settings/volts, no. I highly doubt it. Especially not on that power supply, I've never heard of that brand.

Can it be done, yes. With some tweaking, undervolting, and possible underclock.

Should it be done? Probably not.

Can you just buy an extra 300-400W power supply for ~$20 and use it to run the new card? Or, use a cheap power supply to power the motherboard, then use all 850W to power the cards. I'd stay away from the 7970, still.

Don't use molex to pci-e power adapters!

Thanks for the reply and advice.

Here is the PSU,

http://www.bequiet.com/en/powersupply/212

I was told it was a good brand, but I know nothing about them.

So you reckon 2 7950's and 1 7970 is a bad idea? If so, what about 2 7950's and 1 6950?

Thanks.

[gbeirn]

It's pushing it, especially when overclocked. My Corsair 850 handles 2 7950s overclocked but I had to down clock them to add a 7850

[grums]

It's pushing it, especially when overclocked. My Corsair 850 handles 2 7950s overclocked but I had to down clock them to add a 7850

Thanks, thats good to know.

[slastar]

I had 3x7970@1040/1500 + sempron145 powered by OCZ 850W Gold.  It takes 910W from the wall, working fine for 6+ months but last time change PSU to EVGA 1000W.
BeQuiet is good brand but there is 1 problem with that PSU. It has 4 12V line , better search for PSU with 1 12V line.

[gsupp]

I tried to run 3x Sapphire 7950 Dual-X's (overclocked) off a Seasonic 860w platinum power supply. It worked, but my kill-a-watt meter was showing 1050W drawn from the wall. At 89% efficiency, an 860w power supply shouldn't pull more than about 955W from the wall at maximum load. 100 watts over spec was a bit much for my tastes, so I switched to an EVGA SuperNOVA 1000W P2. I've also killed a 450W no-name power supply with just a single Sapphire 7950 overclocked (ran fine for days, power cycled and it wouldn't turn back on ever again). So it's important to have enough power to run your cards. A fried power supply isn't fun to deal with.

[grums]

I had 3x7970@1040/1500 + sempron145 powered by OCZ 850W Gold.  It takes 910W from the wall, working fine for 6+ months but last time change PSU to EVGA 1000W.
BeQuiet is good brand but there is 1 problem with that PSU. It has 4 12V line , better search for PSU with 1 12V line.

Whats the difference between a 4 12V line and a 1 12V line? Sorry, I just have no idea when it comes to PSU's!

[grums]

I tried to run 3x Sapphire 7950 Dual-X's (overclocked) off a Seasonic 860w platinum power supply. It worked, but my kill-a-watt meter was showing 1050W drawn from the wall. At 89% efficiency, an 860w power supply shouldn't pull more than about 955W from the wall at maximum load. 100 watts over spec was a bit much for my tastes, so I switched to an EVGA SuperNOVA 1000W P2. I've also killed a 450W no-name power supply with just a single Sapphire 7950 overclocked (ran fine for days, power cycled and it wouldn't turn back on ever again). So it's important to have enough power to run your cards. A fried power supply isn't fun to deal with.

Thanks for the post. I was actually running a 7950 on a 425w PSU a well. Worked fine. Have since put that 7950 into my rig and have a 6950 on my 425w now.

[pontiacg5]

I had 3x7970@1040/1500 + sempron145 powered by OCZ 850W Gold.  It takes 910W from the wall, working fine for 6+ months but last time change PSU to EVGA 1000W.
BeQuiet is good brand but there is 1 problem with that PSU. It has 4 12V line , better search for PSU with 1 12V line.

Whats the difference between a 4 12V line and a 1 12V line? Sorry, I just have no idea when it comes to PSU's!

A graphics card not only needs wattage, but amperage. For example, a 7970 is ~250W in a perfect world. That equates to ~21A of power.

Some cheaper power supplies will "sum" the total amperage of several smaller rails to come up with the total wattage available. For example, a 1200W power supply with 6 12V rails is really 6 200W power supplies. You see?

The problem is that for your 850W supply with 4 rails, you've only got 850W/12V = 70A/4 = 17.5A, so you only have 4 17.5A power supplies!!

A 7970 eats 20A in one bite, and if any single rail of your power supply is ever overloaded the whole thing comes crashing down. No single rail on that PSU will run a 7970, it just won't happen. You could divide the 7970 to 2 12V rails, but then you only have two 17A rails left for the PC and two more cards. I don't see that working! One rail with the PC and card (7950) will be too close to max and crash everything. If you had a single rail PSU you would be able to more effectively utilize the amperage available.

So, a multirail PSU is not preferred as it is sometimes not possible to evenly load the individual rails which will cause the PSU to crash. Otherwise, it is perfectly OK.

[gsupp]

Whats the difference between a 4 12V line and a 1 12V line? Sorry, I just have no idea when it comes to PSU's!

Usually the term is "rail" rather than "line". Most of the power a power supply puts out will be at 12 volts. Some power supplies split up the 12V capacity onto multiple rails (kind of like circuits). This is less desirable for mining, since you don't always know which wires coming out of the power supply go to which rail. If you pull too much power from a single rail, you can burn out the power supply. A power supply with a single large 12V rail doesn't have this limitation and you can connect GPUs without regard for how the power supply was designed.

[motatoys]

can I run a 750w and a 1000w different brand psu together if I use this http://coincable.com/product/dual-psu-power-supply-24-pin-adapter-cable/

[Zemou]

I've been mining for 3 months with 4x HD 7950 Dual X on a 1100W PSU. My kill-o-watt shows a consumption of 1000W at the wall.
So you should be able to handle 3x HD 7950 with your PSU.

(My cards are overclocked at 1030 mhz and undervolted)