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Is 750w enough for my rig and 2x780's?

scaryjam823
By scaryjam823
in Power Supplies
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So using calculators online it shows I need about 780w when I get another graphics card and put in sli. But looking around it seems some run them on 750w. With everything I have in my rig (in the sig) + h100i in the future will 750w be enough when I get another 780 and go sli? I had this rig planned for a while back before the 7xx series came out and I forgot to check and update my power supply when I got the more modern cards.

My Rig :  Case: Cooler Master HAF X ,Motherboard: Gigabyte Z87X-UD3H,PSU: Seasonic SS-750KM3,Processor: Core I7 4770k (overclocked 4.7ghz),Cooler: Corsair H100i, GPU: EVGA GTX 780 with acx cooler, RAM: G.Skill Ripjaws 16gb DDR3 1600 (overclocked to 2000mhz), HDDS  Samsung 840 EVO 250 gb SSD , Western digital  2tb 7200 rpm 64mb cache, Old 1tb laptop drive I had , 320gb for os backup daily, 80gb external for weekly backups,Drives 2x Lg Blu Ray burner WH16MS40,MISC: Tp-Link dual band wireless card, Logitech g510s, Razer Deathadder 2013, Acer G236HLBbd 23" monitor, Old tv I had 23" for secondary monitor, old 32" samsung tv third monitor

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out of my head calculation i think it will be ok but dont quote me on this 

If you tell a big enough lie and tell it frequently enough it will be believed.

-Adolf Hitler 

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It should be enough if its a good quality one Linus was running 2 780 ti's off a 700w in the latest build log apparently  

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It should be enough if its a good quality one Linus was running 2 780 ti's off a 700w in the latest build log apparently  

he has seasonic X ,so its a very good one

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You should be fine.

 

Spoiler

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CPU:Ryzen 9 5900X GPU: Asus GTX 1080ti Strix MB: Asus Crosshair Viii Hero RAM: G.Skill Trident Neo CPU Cooler: Corsair H110

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It really depends on the PSU I had to up from my AX760 to an AX860 not because of the wattage but the number of Amps on the 12 volt rail. The AX760 only has 63amps on the 12 volt rail I was pulling around 67 under full load with two GTX780's overclocked causing the computer to shutdown. The AX860 has 71 amps which gave me enough headroom. Lesson learned that watts is not all that matters.

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If it's a good psu, it's plenty. The psu in your sig is perfectly fine for that.

If you ever need help with a build, read the following before posting: http://linustechtips.com/main/topic/3061-build-plan-thread-recommendations-please-read-before-posting/
Also, make sure to quote a post or tag a member when replying or else they won't get a notification that you replied to them.

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It really depends on the PSU I had to up from my AX760 to an AX860 not because of the wattage but the number of Amps on the 12 volt rail. The AX760 only has 63amps on the 12 volt rail I was pulling around 67 under full load with two GTX780's overclocked causing the computer to shutdown. The AX860 has 71 amps which gave me enough headroom. Lesson learned that watts is not all that matters.

 

omg ... you realise that P = U * I ?

 

63A * 12V = 756 Watt

69A * 12V = 828 Watt

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omg ... you realise that P = U * I ?

 

63A * 12V = 756 Watt

69A * 12V = 828 Watt

It is very much possible to exceed your amperage on your 12 volt rail without exceeding your Wattage.

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It is very much possible to exceed your amperage on your 12 volt rail without exceeding your Wattage.

 

The 12v rail on the AX760, as well as many DC-DC regulated PSU is rated as follow: [rated wattage]/12 and rounded down. So that's 760/12 = 63.33, rounded down to 63A or 756w.

 

If you exceed the amperage of the +12v on this particular unit, you are indeed exceeding the rated wattage of the unit.

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The 12v rail on the AX760, as well as many DC-DC regulated PSU is rated as follow: [rated wattage]/12 and rounded down. So that's 760/12 = 63.33, rounded down to 63A or 756w.

 

If you exceed the amperage of the +12v on this particular unit, you are indeed exceeding the rated wattage of the unit.

 

Mine would brown out at 620 watts wall draw however it would reflect 65 amps I can only assume this would come into account from the efficiency factor on the power supply. I would strongly recommend against anything under 850 watts for SLI 780's

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Mine would brown out at 620 watts wall draw however it would reflect 65 amps I can only assume this would come into account from the efficiency factor on the power supply. I would strongly recommend against anything under 850 watts for SLI 780's

 

How does 620w reflects 65A? On the +12v, that's 780w. Unless I'm misunderstanding you, if you had problems with your unit at 620wAC or ~560wDC that the unit is outputting, it would mean your AX760 was defective.

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It is very much possible to exceed your amperage on your 12 volt rail without exceeding your Wattage.

 

nah ... we are talking DC here ... but with high loads you will see a (small) voltage drop, which leads to higher currents ....

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How does 620w reflects 65A? On the +12v, that's 780w. Unless I'm misunderstanding you, if you had problems with your unit at 620wAC or ~560wDC that the unit is outputting, it would mean your AX760 was defective.

Information was pulled from Corsair Link software, 760 was i series. I actually had it RMA'd and had the same issue on the second unit, moving to an AX860 resolve the issue. I would not have believed it myself had it not happened to me, but for OP I can say from experience the 760 was not enough. 

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Information was pulled from Corsair Link software, 760 was i series. I actually had it RMA'd and had the same issue on the second unit, moving to an AX860 resolve the issue. I would not have believed it myself had it not happened to me, but for OP I can say from experience the 760 was not enough. 

 

Oh ok. I was wondering where you got all your numbers from. Is the AX860 also the i series?

 

I'm not sure how it is now, but Corsair Link had been quite inaccurate and buggy. There have been reports of people seeing high +12v readings despite the unit being on idle. There was a long going with issue with one of the members at OCN regarding this: http://www.overclock.net/t/1324891/corsair-deny-all-knowledge-ax1200i-software-broken-probably-applies-to-ax860i-and-ax760i-as-well

However, the inccurate reading was the least of his problems, as he too was experiencing shut downs, that is, to my understanding, only when he enable multi-rail mode. The BeQuiet DPP 1200w he got to replaced the  AX1200i didn't have this shut down issue.

 

Could this possibly be your problem as well? But I guess it is too late to test this out. But saying that you was seeing 65A and yet only 620wAC at the wall shows that there's some inaccuracy in the readings

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Thanks you guys :) I'm assuming no real damage would be caused if I got another 780 and there wasn't enough power? It would just turn off I assume. I had planned to buy a 1200w psu to compensate for the extra graphics card, overkill I know. But I possibly would go 3 or 4 way sli in the distant future. But when I get another card I'll hold off on another psu until I see what it does.

My Rig :  Case: Cooler Master HAF X ,Motherboard: Gigabyte Z87X-UD3H,PSU: Seasonic SS-750KM3,Processor: Core I7 4770k (overclocked 4.7ghz),Cooler: Corsair H100i, GPU: EVGA GTX 780 with acx cooler, RAM: G.Skill Ripjaws 16gb DDR3 1600 (overclocked to 2000mhz), HDDS  Samsung 840 EVO 250 gb SSD , Western digital  2tb 7200 rpm 64mb cache, Old 1tb laptop drive I had , 320gb for os backup daily, 80gb external for weekly backups,Drives 2x Lg Blu Ray burner WH16MS40,MISC: Tp-Link dual band wireless card, Logitech g510s, Razer Deathadder 2013, Acer G236HLBbd 23" monitor, Old tv I had 23" for secondary monitor, old 32" samsung tv third monitor

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Most 780's are locked at 250W at default power target. 

 

Oh ok. I was wondering where you got all your numbers from. Is the AX860 also the i series?

 

I'm not sure how it is now, but Corsair Link had been quite inaccurate and buggy. There have been reports of people seeing high +12v readings despite the unit being on idle. There was a long going with issue with one of the members at OCN regarding this: http://www.overclock.net/t/1324891/corsair-deny-all-knowledge-ax1200i-software-broken-probably-applies-to-ax860i-and-ax760i-as-well

However, the inccurate reading was the least of his problems, as he too was experiencing shut downs, that is, to my understanding, only when he enable multi-rail mode. The BeQuiet DPP 1200w he got to replaced the  AX1200i didn't have this shut down issue.

 

Could this possibly be your problem as well? But I guess it is too late to test this out. But saying that you was seeing 65A and yet only 620wAC at the wall shows that there's some inaccuracy in the readings

Corsair Link worked perfect for me, was fairly accurate between the gpu idle & full load under furmark showed exactly the max power draw that you can read from the bios as difference. You can monitor the pcie cable as well showing the right amps too. If his ax760 failed then it was defective.

 

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