3 7950's on a 850w PSU?

[pontiacg5]

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/

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...

[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/

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?

[pontiacg5]

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/

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.

[MysteryX]

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.

[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!

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.

Hey,

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

Cheers.

[Gazza1]

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.  

[rext]

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

[utlord]

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

[badbrains]

(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.

[Hippievogel]

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.

thats not true it depends on what 850 you have.

[PrintMule]

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.

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.

[grums]

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.

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.




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.

[pontiacg5]

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...

[xgtele]

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

[grums]

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...

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.

[zackclark70]

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

[PrintMule]

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.

[Gazza1]

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

[grums]

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...

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!

[U1TRA_L0RD]

You need atleast 950 w PSU for that.