Bitcoin Forum

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.

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.

;)

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.

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

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.

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

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.

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.

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.

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.

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!

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.

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.

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.

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/

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)

So long as you are aware of the rail configuration of both power supplies, as well as the proper loading of each supply, then yes.

You don't even need that cable, it's a fiat trap for noobs. Get a staple and short that beast. Use the switch to turn it on and off, but this is mining and we never stop  ;)

http://www.overclock.net/t/96712/how-to-jump-start-a-power-supply-psu-test-a-power-supply-and-components

Try not to run an ATX power supply without some sort of load on it though. I'm not sure if this is still the case, but older ones couldn't regulate without some load on them at all. The fan in the supply itself ought to be enough...

Thanks for the reply and here is some info, the 1000W power supply has one 12v rail which has a total of 83 amps on it and the 750W psu has 4 12v rails with 20 amps each, with that said am I safe to use them together to power some 280x? if I am should I use the 1000w to power the motherboard + 2 cards and then the 750w to power 2 more cards?

You've got it. Make sure those 280x cards on the 750W supply are wired to two of the 4 rails apiece and you'll be good.

I've been running undervolted and overclocked sapphire reference 7950's off of 850w gold power supplies for a long time, the 3 cards and ssd / celeron cpu only pull a touch over 700 watts at the wall. If you have voltage locked 7950's then thats a different story, they drain power like a mofo.

Hey,

Thanks alot. This post was extremley informative and helpful. I know what to look for when I get my next PSU now!

Cheers.

I've got an 850w gold powering 3 280x
I've also got another 850w of the same psu powering another 3 280x and a mobo/cpu/ram on a different machine

The PSU's are not pushing out hot air (just regular warm air) nor are the fans spinning fast which leads me to believe they are doing just fine.

I do undervolt everything though.  

Maybe you can get a 900-1000w psu to be safe

Im running r9 290 + r9 280x + 7870 on a 850w XFX pro PSU. Works fine:)

(2x) 7950 1.081v and (2x) R9 270 1.075v on Corsair RM850. 4 rigs with this setup on 240V circuit. If possible run your rigs on 240V, you'll get a higher efficiency from your psu and it cuts the required circuit amperage in half compared to 120V.

thats not true it depends on what 850 you have.

Not only. Cards also run less hot when hashing vs when gaming. You can test that by running low cpu usage bench. Amount of resources used differs a lot.


Anyway, my best advice to anyone would be - even if it runs stable for 10 hours, do not leave it unattended for long, or without some fail-safe solution.

Hey,

I just figured out my PSU has an option to switch from multi to single rail.

"the white socket labeled OCK is used to set the power supply to either single or multi +12V rail mode. With nothing connected, the power supply will operate in multi-rail mode (+12V1, +12V2, +12V3 and +12V4). Plugging in the small jumper or connecting the PCI bracket mounted switch (and turning it on) will disable the individual +12V rail OCP circuits and enable single rail mode.

I havent touched it yet though.

Also I need some help figuring out how to connect the 3rd GPU which arrrives tomorrow.

Here is the connections on the back of my PSU.

http://s29.postimg.org/rv2gdmd6f/P9_850w_11.jpg


I only have cables for two of the PCI-E slots. Each cable has a 8 + 6 pin coming from it into the GPU.

However, I am unsure of what type of cable this is. If someone could give me the name of it or link me where to buy one that be great as I need one for the third slot. I have another thread on here about this as well. Heoping to have everything sorted by tomorrow night.

Thanks.

You'll likely need to make your own cable, if you can't find one to order by google searching I won't be able to either. It will be propitiatory to that power supply, so it doesn't have a name.

Either that or run the cards off sata to pci-e adapters. This will probably be the quickest way to get set up. I'd then go on digikey, find a mate to that mini-fit jr. connector on the PSU, then make your own pigtail using the pci-e plugs salvaged from the sata to pci-e adapters you bought. That's kind of unnecessary and exceptionally hard to explain though, I still don't really know how I cruise datasheets like I do...

http://www.amazon.com/Branded-8inch-15pin-Express-Power/dp/B005NJXY7O

Or, you'll get lucky and the cards will come with sata to pci-e adapters! I don't trust the 4 pin molex ones...

850W gold rated PSU can easy handle 3x7950 without any problems 24/7

Thanks again for the advice.

Yeah, its fairly awkward for me to undertand. Seems like alot of effort. If only I could have found that cable online. (Much easier) I made a post in the support forums for that PSU as well, just to see if there is anywhere online I can purchase one of them cables.

If not I will do it the way you mentioned.

I have a rig that's been running 7 months with 3x 7950s getting 1900kh total  on a hx750 psu pulling 700w from the wall

psus differ very much, despite the label. Some may even work above reported load for hours, while other die at 80%. There's usually a number on a label per each rail or set of connectors for MAX load.

http://www.techpowerup.com/reviews/NOX/Coolbay_HX_APEX_700W/images/psulabel.jpg

I ran 2 7970s on an Antec 520w for a few months last year.  The 520w is still in good shape.

Good news!

I emailed Be Quite last night asking if I can get that cable anywhere. They emailed me this morning asking me for my address. Said they will post me one free!

I also connected that single rail switch as well. Didnt even know about it till yesterday. I have learned alot from this thread!

You need atleast 950 w PSU for that.

cheap brands/ cheap psu always combine the total load as you can see it is a 700w psu(If you look better you can see the load on the 12V is 600 only), mine ax860's can handle 852 alone on the 12V)
I think the way to go psu's are the ax860,ax1200(7 Years pick up warranty), some platinum seasonic's, Lepa g1600(not sure about warranty but 5+ years for sure) and the Evga Supernova 1300 G2(10 years warranty). I dont see any other Psu being a good bang for buck value.
http://www.techpowerup.com/reviews/Corsair/AX860/images/box_rear_close9.jpg

EVGA Zupernovas <3 G2 1300/1000 and P2 1000 are all great in my book.

Too bad they are gone nearly everywhere, and anywhere they are to be found is $50-75 over retail, and $100 over what I paid on black Friday...

Guess I have good taste in hardware  ;D

And the 1.5K supernovas are unstoppable beasts, as in they will give you 12V till the wiring in the wall melts. Here is one running 5 290's at clocks that are no slouch, I left this going for a few minutes then stopped it before I burned my house down  ;)

http://i879.photobucket.com/albums/ab357/pontiacg5_2010/IMG_20140203_214906_zpsfceff734.jpg?t=1391618115

They will do more on 240V  8)