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Repeated PSU failure, 12v rail overloaded?

Last response: in Components
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July 17, 2011 2:07:46 AM

Hi all, I really need some help here, I have had 3 PSU’s die on me in the space of a few months.

First was a Antec 500w, I had that one in my system for at least two years, died about two months ago.

Second was an OCUK 750w, “partially” died about a month after but with the odd querk that it would start up and run normally as long as the room the PC is in was very warm (>25 degrees c)
Gradually it lost the ability to boot the system or do anything other than spin the case+cpu fans under anything less than a ridiculously high room temperature or by booting it with a hairdryer in the air inlet (yeah seriously!) up until this point I didn’t suspect anything other than the 1st PSU had died of old age and the second was DOA with a faulty thermal breaker, sadly I bought it off a friend (unused and boxed) so couldn’t RMA it.

A week ago I got PSU #3, a Corsair 500w, again... dead within a week, this time I happened to noticed that it died under heavy load playing Fallout: New Vegas.

System specs:
Pentium core-2-duo E6600
2GB DDR2 Ram
Radeon HD5850
Harddisks: 4x1TB 7200rpm SATA
DVD-RW
Auzentech Xplosion 7.1 dts soundcard
5 USB devices

The system hasn’t changed from since the first power supply until about a year ago when I swapped out my old radeon X800 for the HD5850 and added another 1TB 7200rpm SATA.

I suspect what’s happening here is the PSU’s are being overloaded but I want to be as sure as possible that’s the case before dropping in yet another replacement.


Skip this paragraph if you don’t want the maths:
The max power consumption of the HD5850 is rated as 160w. So that’s 13.3 amps just for the GPU alone, another 80w / 6.3amps for the max THD of the CPU but I’m lead to understand that actually hitting that 80watts is unlikely. Also 20w /1.6amps max for all 4 HDD’s *if* they were all read/writing at the same time.

TL/DR:
Total theoretical max should be about 28amps, and the PSU calculator at http://www.extreme.outervision.com/PSUEngine seems to agree with me at 27.2amps (12v rail only)

The first PSU that died was rated at 18amps, second was also 18amps, however the 3rd and brand new CX500 that only lasted a week was rated at 34amps, a fair bit above my theoretical max.
(note: I have no idea about the first two PSU’s, but the CX500 is advertised as having a single 34amp 12v rail)

-Could it possibly be that the CX series just isn’t up to powering a system that close to the line? (I estimate 390-400w total on a 500w supply, peek load of 27amps on a 34amp rail)

-Could the 5v rail (much more difficult to calculate) be the limitation?

-Or is it just more likely that I have a freak component / bad motherboard / something drawing farrrr more power than it should?

-Or as this article seems to recommend, that a system built around a HD5850 really does require a minimum of a 40amp 12v rail (something AMD doesn't mention, their website says only that a 500w PSU is sufficient )
a b ) Power supply
July 17, 2011 2:51:04 AM

For goodness sack, get a corsair or antec with 40 amps or more on a single 12v rail. They don't cost that much more. Newegg has them on sale all the time with rebates.
July 17, 2011 2:58:31 AM

o1die said:
For goodness sack, get a corsair or antec with 40 amps or more on a single 12v rail. They don't cost that much more. Newegg has them on sale all the time with rebates.


Yeah I'd like to be sure that the 12v rail is the issue before I drop yet another PSU into the system, I'm not certain it is the issue because:
1st PSU rated at 18amps - lasted over a year.
2nd PSU rated at 18amps but 250w more - lasted a month, but may have been DOA.
3rd PSU rated at 34amps - a decent margin above the calculated requirements of my system - lasted a week.

I hope you can see why this is causing some confusion :) 
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a b ) Power supply
July 17, 2011 2:54:26 PM

might be blown caps or vregs on your board or some minor short somewhere causing the psu failures over time
July 17, 2011 3:40:41 PM

The Corsair one must have been DOA because the CX series is fairly good quality and I think it should have no problem with your specs. However, as suggested, get a PSU with a powerful +12V rail. I would recommend this one: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Or if you want to have some more headroom, get this: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Or this, if you want modular: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
a b ) Power supply
July 18, 2011 3:57:40 AM

its not a super high powered system, a 500w antec or corsair should be enough. I suspect there is some fault, maybe your electrical wiring in your house, or maybe a faulty component in your PC causing the issue. Buying a higher power PSU may just mask the problem.
a b ) Power supply
July 18, 2011 11:15:42 AM

You may also try a different surge protector in case the problem is from the wiring in your house as the previous poster pointed out.
!