Using 2 PSU , Good or Bad ?

[arvindsagar702]

Heya, so i got myself a cheap Gigabyte r9 280x just a few days back and i want to power the second gpu using my corsair vs550w psu .

I already have an Antec Vp650p v2 psu but i dont think it can power 2 r9 280x (i know there are many threads out there but i havent found any gpu deaths because of this or as close to what i am about to ask).

So i ordered an Add2PSU today and will see how it would help . Still , they say if we use 2 PSUs then the uneven voltage on the same card might kill it so i was wondering if i could just put both of my 280x on the corsair 550w and the rest of the system on antec. I think both will be at around 500w so that should not cause any uneven voltage trouble , still this could also mean that i kill both of them at once.

So should i go with this or just use the second psu for second gpu ?

I calculated using many calculators and the pc will draw 786w so i need atleast 800w to not tax an ups .
I cannot buy an 850w psu as my budget is $100 and the cheapest reliable psu of 850w costs $92 on amazon.com plus $104 for shipping so its around $196 and they wont even pay the customs (talking from experience) which would be around $50 so basically $250 . And local online shops in India sell 850w psu for $200 or more. Yes i have researched all that i could and i have come across 0 850w psu in $100 or so , the cheapest low tier corsair is even $150. And no i cannot put in more or go to china to buy them as i am just 17. Yep searched second hand websites too,same case.

And no i cannot sell the 280xs basically because a gtx 1070 costs $500 or so here while the 280x could be sold for $200 each which will even take months . Second hand gtx 1070 cost $350 or so . And i cannot sit without a gpu so thats another problem.

My specs :
CPU - AMD FX 8350 running stock everything
GPU- Sapphire R9 280x vapor x
+ Gigabyte R9 280x
Ram - 4gbx2 corsair value select + gskill 8gb , all running at 1600 mhz
Hdd - 7.2k rpm 1 tb x3 hdds
Motherboard- Gigabyte G1 990fx
PSU- Antec Vp650p v2 + Corsair Vs550w
OS- Win 10 enterprise insider preview x64 build 16251
Case- Deepcool DuKase v3
Fans- 4 120mm + 2 Server delta fans 80mm

 

[Solandri]

While it can be done, it's not recommended because the results are unpredictable. You could use the second PSU to power parts of the computer which are electrically mostly isolated. e.g. The HDDs don't really care of the power they're getting is the same as the power the rest of the computer is getting (which is why external drives work just fine).

But a GPU is getting power from both the motherboard (via the PCIe socket) and the 6- or 8-pin direct connection to the PSU. If you plug one PSU into the motherboard, and a second PSU into the 6- or 8-pin, it will work fine if both PSUs are putting out the exact same voltage. But if one PSU is putting out (say) 12.15V and the other PSU is putting out 12.0 V, that difference of 0.15 V will cause stray electrical currents between the 6- or 8-pin and the PCIe socket. Whether that stray current does nothing or causes the GPU to fail is completely unpredictable. You're using the GPU in ways it wasn't designed to be used (different voltage across components which the designers assumed would be at the same voltage).

The systems specially designed to take two PSUs (or two AC power adapters) have extra circuitry which combines those into a single voltage before sending it on to the computer.

 

[Kasper Jorgensen]

You are indeed on deep water here. I recommend you to not doing it and buy a good PSU with the wattage you need instead. You could risk frying your whole system in worst case by doing it.

 

[arvindsagar702]

While it can be done, it's not recommended because the results are unpredictable. You could use the second PSU to power parts of the computer which are electrically mostly isolated. e.g. The HDDs don't really care of the power they're getting is the same as the power the rest of the computer is getting (which is why external drives work just fine).

But a GPU is getting power from both the motherboard (via the PCIe socket) and the 6- or 8-pin direct connection to the PSU. If you plug one PSU into the motherboard, and a second PSU into the 6- or 8-pin, it will work fine if both PSUs are putting out the exact same voltage. But if one PSU is putting out (say) 12.15V and the other PSU is putting out 12.0 V, that difference of 0.15 V will cause stray electrical currents between the 6- or 8-pin and the PCIe socket. Whether that stray current does nothing or causes the GPU to fail is completely unpredictable. You're using the GPU in ways it wasn't designed to be used (different voltage across components which the designers assumed would be at the same voltage).

The systems specially designed to take two PSUs (or two AC power adapters) have extra circuitry which combines those into a single voltage before sending it on to the computer.

Yea i get that part and thats why i said i could just try to make their loads equal. Well anyway you say that the current at 12v might become issue, so https://www.oldi.ru/upload/resaiz_images_catalog/big/102/237658/0241102_10.jpg is my antec (btw it says 35A at 12v1 and 35A at 12v2 so does that make 70A ,it makes about 800 watts when we do maths but is kinda weird since its rated 650w so whats your opinion on this , i mean putting both gpu on it can i trust it ?) . And https://f.ptcdn.info/363/010/000/1380548754-6471211370-o.jpg is my Corsair . Indeed though there might be voltage difference , Also , how can i test both my supplies to check their voltages and even out the difference ? I mean can we not like put something and make the voltage low or high for whichever one we want. I am really tight on budget here and I already have all these things .

 

[arvindsagar702]

You are indeed on deep water here. I recommend you to not doing it and buy a good PSU with the wattage you need instead. You could risk frying your whole system in worst case by doing it.

As i said, i would if i could but I simply dont see myself holding $200 in the foreseeable future.

 

[Kasper Jorgensen]

Eventually sell your current PSU first, that should get you on the way to $200.
If you wanna try this or not is up to you, but it is absolutely not recommended and basically everything could happen from unstable system to a complete failure of every component inside your computer.
Basically you asked if using 2 PSU is good or bad, I can tell you that it is bad.

 

[arvindsagar702]

Hey so theres this offer for an old cm gx 750w psu nearby , its out of warranty is about $70 so i think it should be better than 2 psus and way less risky even if it would basically be working its ass off all the time. The seller says its working great and has never had any issues , plus i am pretty certain that i would be able to buy an 850w psu in 2 months. So should i go with it ?

 

[Kasper Jorgensen]

Then wait and stick with one GPU in your system for now. That old Corsair CM PSU is very crap.

 

[arvindsagar702]

Yea but if anything would crack up it would be that gx 750w. Ik i could just save money but then i just dont wanna wait 2 months to try out cf . So in the end it is , either burn $70 on a psu that might or might not crack up or just use 2 psus which will crack up everything or sit with 1 gpu. The time period wont change since i basically will get money only after 2 months.

 

[Kasper Jorgensen]

If that low quality PSU cracks up you risk frying your whole system and setting your house on fire. That's the reason for always getting a good quality PSU

 

[arvindsagar702]

Heyyy thanks for the heads up , i was almost certain that gx 750w wouldnt cause trouble. But after reading reviews even deeply and learning about ripple i think the pro rippler gx 750w + its old age here is gonna give a really bad current . Well yea i am gonna save for a better psu now but i foudn this https://www.techspot.com/community/topics/2-psus-powering-1-computer.199807/ . Multiple reports of people running dual psus with no problems,heck there are even cases meant for 2 psus so it might not be 100% safe but considering how my 580w system survived a corsair vs550w for 2 yrs and still no probs i think 2 psus will be a better idea . Just wanna know tho, what is common grounding and how to achieve that ? Cause that seems to help even out the voltages for other people.

 

[Kasper Jorgensen]

Well, use that at your own risk.

 

[arvindsagar702]

Thanks for answering both of you but i just had 1 last question. So i calculated and each 280x takes 250 watts and the fx 8350 takes 125 making total power draw of 625 watts. So can i not like just use 1 psu for motherboard+cpu+gpu+gpu and the second psu for just 3 hdds and 6 fans ? That would cut close at 650watts and the Antec VP650p v2 should be able to handle that since i do no oc. This way the 2 voltages literally never meet up and i get my safe setup so it should be a win-win.

 

[Kasper Jorgensen]

250+250+125 gets 625w leaving only 25w for the mobo and ram. Well, it may work out just fine but on the very limit and with no overclock.