Pc psu problem

[SWAGNOOB]

I have a 850w psu that has 16amp on dual 12v rails.My power usage monitor shows that the pc is using 520w on idle and 640w on full usage.My problem is that when i run any 3d app for any length of time, the psu shuts down and reboots the computer.Ive checked the psu with my tester which says it's fine, checked wattage and temps, again fine, and cannot fathom why the psu would act in this way.Does anybody have any idea's on what could be causing this?

 

[Grossel]

What type of power usage monitor are you using?

 

[SWAGNOOB]

Maplin N67FU

 

[Grossel]

Is that a problem also when not using the maplin?

 

[Ian Rogers]

If its a modern PC, it might not be a PSU problem... Most motherboards have control of the PSU and can stop / restart it if there's ANY problem in the PC ie overheating etc..

What video card have you installed.... Has it got an extra power connector? Another problem, (I had at least) was the main CPU wasn't cooling properly, the symptoms were exactly as you described.

 

[Sceadwian]

My problem is that when i run any 3d app for any length of time

Has it occurred to you that the video card is faulty, or perhaps that your power supply unit has too much voltage drop for the video card to tolerate under full load, or even that the video card itself is overheating and causing the reboots? Why on earth did you start looking at the PSU as the culprit and what makes you think it's what's rebooting the machine?

 

[vedo35]

i got almost same problem. first start to job change capasitors on psu or video card. On psu secondary side chage all capasitors and on video card change also all capasitors. My video card was freezing i changed all capasitors and were normal. Try first this.

 

[SWAGNOOB]

Morning guys, thanks for showing an interest in my problem.I will try to answer your questions as best i can

Grossel - yes, with and without.

Ian - The system is 6 months old. Specs are- watercooled AMD1090t running @ 29c idle/62c full load.Crossfired ATI HD5750's running @ 35c/38c idle and 62c/65c full load.

Sceadwian - The reason im looking towards the psu is because as soon as i remove any one of the fans from the motherboard connectors,the problem stops.

Is it possible that im asking too much of the motherboard power and could moving some of the extra fans to a spare molex cable(with nothing attached) rectify the problem?

 

[Grossel]

Grossel - yes, with and without.

Then the maplin is not the problem.

Sceadwian - The reason im looking towards the psu is because as soon as i remove any one of the fans from the motherboard connectors,the problem stops.

I have an old computer (built in 2005) that suffers from the same failure.

I then found that:

• The chipset fan was broken - failure started aprox a month before the bearings failed.
• CMOS battery was about to empty.

In my case, the combination of those two made the computer act on a similar way as you explain.

 

[Sceadwian]

You may be using faulty metrics. You said your supply was 850 watts, and you're wondering why things are failing because you're only drawing 640 watts.. What you're failing to take into account is the 850 watt rating of the power supply is for ALL rails combined. The actual power rating for each rail separately is always much lower, there's a very good chance that you're over taxing one of the 12V rails under this false asumption that because it's an 850 watt supply that it should be able to do 850 watts on the two +12V rails, this is not the case. You'd have to measure the amperage on each separate rail and compare that to the listed specs of the supply (they do list the max current for each separate supply along with the total wattage limit)

Suffice to say you may be using a power supply that doesn't meet the system needs, not the PSU itself being faulty. It's very possibly a system design fault not an actual device fault. Toss a 1500 watt supply in there and see what happens. NEVER go cheap on your power supply, and ALWAYS over engineer or you run into these kinds of problems.

 

[SWAGNOOB]

Thanks sceadwian, you were bob on , i was overloading the motherboard rail.Ive moved the extra fans to a separate molex cable and bingo, problem solved.Ive even managed to put a cold cathode on the alternative cable without fail.Thanks again.

 

[Sceadwian]

For long term system stability I would suggest.. even though it works now you may want to invest in a better power supply, or at the very least determine what percentage of the existing supplies capacity you're loading. The less you load it the longer it will last and the more stable the system will be as a whole. I am BIG fan of de-rating especially consumer devices. I'm personally uncomfortable loading anything I 'trust' to more than 50% of it's listed capability.

I like a lot of wiggle room.

Every inch closer to the 'line' you run a device is an inch further away from having it there if something goes wrong.

 

[Ian Rogers]

Two ATI's both requiring extra connectors? If this be the case your 850watts not big enough