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I'm having an issue with my PC: It is rebooting sometimes, and I am suspecting the PSU, so I want to confirm a few things. It is a new PC and the first issues started occuring roughly one month after purchase. Also they only occur after several hours of usage. And it seemed that completely shutting down powerline to the PC, and waiting few minutes, then putting it on again, seemed to relief the issue, but that might be just coincidence?

First off:

  • Does the PSU capacity decrease over lifetime of the PSU?
  • Does the PSU capacity temporarily decrease as it is active for a continious time?

My PC specs: Intel i7-3770, 16GB RAM, GTX 770, SSD, HDD. I think Asus Z77 motherboard.

As you can see it is pretty high-end, but I rechecked the PSU on the invoice yesterday and to my surprise I found a 30 euro PSU, namely the HKC V-550.

My system draws 480W of power from the powerline, if on full GPU & CPU stresstest. This is a heavily modified version of their base system, which did not include such a high-end GPU as the GTX770.

Also, as far as I know, a system shutdown (without! bluescreen) can only occur, if:

  • PSU shuts down
  • CPU shuts down
  • Motherboard shuts down?

But to me it occurs to be logical that the PC would not reboot if the CPU or Motherboard had shutdown, yet with a PSU and a safety switch it might seem logical that it could reboot.

Also about the reboot: The PC "on"-LED in the front turns off once it reboots, and in my headset (that is connected through USB) I heard some kind of clicking sound once when it turns off, and once when it turns on. Might that be enough reason to believe that it is the PSU?

Also, the temperatures of my CPU and GPU, actually of my whole PC, are perfectly fine under load. The only real test I have not been able to do yet is Memtest86, but wouldn't that lead to a bluescreen under windows anyway? Instead of a reboot.

Well I hope someone is able to help me here.

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please explain what a stress test is? there is no such software that can accurately measure the amount of power your computer pushes without a power adapter like kill-a-watt –  Sickest Sep 23 '13 at 7:28
    
A stress test does not measure the amount of power the computer pushes, rather it pushes the computer to use a lot of power - and thats the point the OP was making - when doing a lot of computing the system is drawing 480 watts - which he is - I think correctly - postulating might be the cause of his problems as the PSU can (I suspect) only handle 550 watts, and thats not a big margin. –  davidgo Sep 23 '13 at 7:35
    
Check in the power section for the "ac Restart" option or start on power, or whatever they call it this week. It does sound like a shutdown, not a crash. and unstable system asus MB can certannly bail out like that without it being an actual power issue. If your showing a 480W use though, and using only a 550, the spikes could still trip it. Could be anything. Lower your power consumption (somehow) without changing the clock and ram and all that. see if it still does it. If there is nothing to pull, then downclok the graphics card, that will get you some leeway to test. –  Psycogeek Sep 23 '13 at 7:43
    
Some components may draw more current from time to time, even taking HDDs for example, when they have to spin up, they require more energy and the load for sure is dynamic and change with time, so you may not have enough wattage –  Ashtray Sep 23 '13 at 8:49
    
At 30E and 550W, your PSU is almost certainly a low quality one that's unlikely to perform well at its listed rating if it's capable of. A good PSU in that power class should cost at least twice as much. –  Dan Neely Sep 23 '13 at 13:28

4 Answers 4

up vote 23 down vote accepted

To those who feel like commenting on this answer or even downvoting, please make sure to read it in full and check out the links before you do so. Constructive criticism is by all means welcome, but I don't fancy fielding comments that are already covered by the answer itself. Thank you.

It seems like your current power supply is underrated for the load you are putting on it. As you found, the PSU can provide a maximum of 24 A on the single 12 V rail (288 W), while the GTX 770 supposedly (according to the OP's comment) needs 42 A at 12 V (504 W); @davidgo found a TDP of 230 W for the GPU itself, which goes well with figures published on Tom's Hardware saying about 250 W is needed. The graphics card drawing "just" 250 W would still leave very little margin for anything else on 12 V when the graphics card is working hard. Things that run on 12 V are usually those with motors: spinning-rust hard disks (clocking at about 10 W apiece when working, more on startup), fans, and (as you have found out) some high-powered electronics. To prevent worse problems, including short circuits, the power supply might very well be designed through either a current or thermal trip to shut down in case of an overload.

As this is a card you apparently have added yourself, you shouldn't expect the supplied PSU to be dimensioned to handle such a load. Keep in mind that the typical idle power consumption of a desktop computer is 60 W, and on the order of twice that might be a reasonable figure for a fairly typical computer (except the monitor) under load.

You should look for a power supply that is rated for the necessary load on the appropriate rails. Since you'd need to supply at least around 50 A on 12 V (600 W there alone) to guarantee enough power for the graphics card if it really draws 500 W, you'll be looking at power supplies at least in the 800 W and up range. If the graphics card draws on the order of 250 W, you might easily get away with a 500 W PSU. What is most important (more so than the total wattage rating) is to pay close attention to the rated amperages on the different rails and the requirements of your particular graphics card and through the motherboard the CPU (since those two by far will consume most of the power unless you have an insane number of other pieces of equipment in the computer) so you don't end up with another power supply that exhibits the same problem.

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After a bunch of comments and replies, this seems indeed exactly what is going on. –  skiwi Sep 23 '13 at 9:31
    
The GTX770 doesn't need 504W, see this : tomshardware.com/reviews/…. You rarely need more than 500W total if you're not running multi-GPU or a dozen of hard drives. –  Kwaio Sep 23 '13 at 9:48
2  
@Kwaio Did you actually read my answer before commenting? I linked to that exact page. Even with the graphics card "only" needing 230-250 W, you're left with at most about 50 W margin on the 12 V rail. The CPU draws another 77 W, presumably of 12 V, which even without considering anything else instantly puts you over power budget by at least some 20 W, and likely by about 40 W on the 12 V rail. 40 W over PSU spec is about 15% too high for the power supply to handle within its rated load, which is non-trivial; then add everything else 12V. –  Michael Kjörling Sep 23 '13 at 9:53
1  
Indeed, I stopped when i saw something stating a GPU would draw 500W. I should have read the whole post. Just note it may be mistaking for some people who, like me, would make the error to stop after the first paragraph. –  Kwaio Sep 23 '13 at 11:05
1  
@DanNeely I clarified just now that the number 42A at 12V is from a comment by the OP. The sentence goes on to cite the figure ~250W from Tom's Hardware. Both statements are linked to their respective sources. None of these change the basic premise of my answer, however: the simple fact is that the PSU is spec'd for about 290W on the 12V rail, and with a CPU max TDP of 77W (and assuming that's drawn on 12V) it does not matter whether the graphics card draws 250W or 500W, you are still over the power budget on 12V at peak power usage even before considering everything else that wants 12V. –  Michael Kjörling Sep 23 '13 at 13:50

It is possible that the power supply is faulty and causing the PC to shut down.

Your hypothesis that a system would reboot if there is a CPU or Motherboard fault is reasonable, although it is conceivable that it could cause a shutdown (particularly the motherboard).

If you need to leave the PC for a few minutes before a reboot will work, this is also a strong indicator of a PSU problem.

It does seem to me that that size power supply (unless its a very good one - unlikely at $30) might be on the low side. The GPU has a TDP of 230 watts by itself, with the CPU having a TDP of 77 watts, so thats 305 watts excluding the motherboard and CPU - so your 480 watt figure sounds right. I'd be inclined to believe the PSU might have been working too hard and is now not able to handle the load.

share|improve this answer
    
Ok. I'll go to shop that put my PC together as soon as possible and explain the situation there. In my opinion this should be under the warranty if they delivered a PSU that is not capable of running the system. Might want to add that this is a heavily modified version of their base system, which did not include such a high-end GPU as the GTX660. –  skiwi Sep 23 '13 at 7:38
    
If you were in New Zealand, you would be covered under the Consumer Guarantees act for something like this. I hope your consumer protection laws are decent - and yes, I think they should be paying for a replacement PSU if they specked the machine. –  davidgo Sep 23 '13 at 7:40
1  
Even more important, I think, is that you can be overloading the PSU even without being anywhere near the total rated maximum power output of the PSU. If you are overloading a single rail (basically, output voltage), you can see power issues even though the total power consumed is considerably less than the PSU's maximum rated output. For example, it does you little good to have plenty of power to spare on the +12V rail if you are overloading the +3.3V rail. With a highly asymmetric power load on the various rails from having added high-powered hardware, this is a very real possibility. –  Michael Kjörling Sep 23 '13 at 7:47
    
Would it be possible to make any proof (perhaps via another post on the internet), that my GPU (perhaps in combination with other hardware part) is overloading a single rail on that PSU? –  skiwi Sep 23 '13 at 8:36
1  
@skiwi I would say that is definitely your problem, then, or at the very least strongly related to your problems. (By the way, you said GTX660 in a comment above, and I didn't catch that when incorporating it into your question. You may want to edit the question to correct that, whichever happens to be correct.) –  Michael Kjörling Sep 23 '13 at 9:04

To answer your first two questions: Yes, and no.

I'd lean more towards a PSU myself, as that power supply that they? provided you is absolutely garbage as their 12V ratings are very low. When the 12V is overloaded it can cause the whole PC to reboot, and with a 770 you're definitely pushing the limit on it. If you're comfortable enough working inside the computer and you've got a video connector on-board your motherboard, try unplugging the GPU's PCI-E cables that lead to the power supply, move the video input to the on-board video connected to the motherboard and boot up your computer for a while. If it stays stable longer than "several hours", you've probably narrowed down your issue. You'll need to contact whoever sold you that thing and have them get you a power supply that isn't made from the junkyard scrap.

share|improve this answer
    
The PSU is probably (I haven't looked very closely) fine for the original hardware, but adding a 230W graphics card pushed it over the top. The odds that any computer manufacturer would put in a PSU rated for twice the expected peak load are pretty slim. It's not only about total wattage, it's about amperage at different voltages. You can overload the latter without overloading the former. Note that the original system configuration did not include the GTX660. –  Michael Kjörling Sep 23 '13 at 7:55
    
So OP added in a dedicated GPU after receiving it from this store who built it for them. Not the best of ideas and the blame doesn't lie with the store, but it does still seem weird to put in a really shoddy (as far as quality and amps across the rails) power supply with a high-end configuration even without a dedicated GPU, since a quality 550W PSU should be able to hold its own with a GTX 770 inside. –  Ben Sampica Sep 23 '13 at 14:41

Does the PSU capacity decrease over lifetime of the PSU?

  • PSUs, like most modern appliances, broke with time. Cheap PSUs broke faster. But yours is a new one.

Does the PSU capacity temporarily decrease as it is active for a continious time?

  • It depends on the load and the quality of the electronics.

PSU is one of the most important parts when you are building a rig, and yet it is often one of the most overlooked parts, along with the motherboard. PC vendors usually mount cheap PSUs to cut costs, even in medium to high end PCs. You need to decide whether you would want to keep going on for some time with a crappy PSU and replace it when it brokes, or buy a good one from the beginning that would work fine for your PC's lifespan. Being a high-end PC I would choose the latter, specially because a faulty PSU can fry your motherboard when it stops working normally.

I personally have bought a high end PC in the past, and I selected one of the best mobo's at the time, good GX card, best HDD, everything from reputable brands. But the vendor sold me a cheap $40 PSU. It wasn't the cheapest available though. Two years later it started failing randomly, causing boot loops. Turned out a capacitor has blown out. Replaced it with a decent PSU (Corsair) and everything is ok.

So my advice: go to the store where you bought the PC and have them diagnose the PSU. If it turns out to be faulty, try to replace it for a better one, and pay the difference. Spare no expense on it, expect to expend $100+ on a good one if it is brand new.

share|improve this answer
    
"PSUs, like most modern appliances, broke with time." The OP's problem is that there's an added graphics card which alone requires twice the 12V amperage that the PSU can deliver (let alone everything else that runs off of the 12V rail). That is not about a low or high quality PSU, and it's not about age; it's about rated output wattage and amperages on the PSU in question. A high-quality low-powered PSU would not do any better. –  Michael Kjörling Sep 23 '13 at 9:34
    
@MichaelKjörling I've no time to make the PSU calculations, and I'd rather let the more experienced users to make a proper answer. Other than this, my answer was not intended to be the solution, but a general recommendation, and it is still valid. Do you really think a low quality PSU, even if it fulfills the Wattage budget, can't broke for different reasons? –  Mister Smith Sep 23 '13 at 9:43
    
Of course a low quality PSU can go bad, but that is not the case in the OP's situation. It was stated in a comment about 20 minutes before you posted your answer that the PSU can deliver 24A at 12V while the graphics card alone needs 42A at 12V. Stack Exchange is aimed at solving specific problems, and this answer does not offer any real guidance for the OP (the PSU is probably working within specifications), so in the context of this question, this answer is not useful. –  Michael Kjörling Sep 23 '13 at 9:49
    
@MichaelKjörling Well that's your opinion. You are free to downvote. I'd understand critics if I'd have said something incorrect or misguiding, but I think my answer is perfectly fit for the site and can help other people. BTW, I'm no noob on SO. –  Mister Smith Sep 23 '13 at 10:18

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