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Why are good, expensive PSUs failing?

In the last two to three years I have had to replace the power supplies (PSUs) for my main computer with units of continully increasing wattage (650, 750, 850, and 1050 watts) at least 6 times.  This are good, expensive name brand PSUs that the manufacturer has replaced under warranty.  The brand new 1050 watt unit recently began causing BSODs, so I had to put the 850 W unit back in.  I operate these PSUs at 1/2 to 3/4 of rated wattage; e.g., the present 850 W unit is supplying 620 to 665 wildly varying watts.  Last night I was watching the GPU-Z output of the power demands of two Nvidia Geforce 570 GTX display cards, which both erratically varied between 22 and 55 Amps (at only 1 volt) as they processed Seti@Home work units.  Is it possible that the switching unit of these switching PSUs cannot keep up with these wildly varying power demands and so is failing?  Is it a good, bad, or neutral sign that the PSUs 12-volt rail is outputting at present 18.82 volts measured by a VOM at a Molex hard disk connector?
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CElliott2
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CElliott2
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7 Solutions
 
John HurstBusiness Consultant (Owner)Commented:
620 to 665 wildly varying watts.

That is not a wildy varying range, so I then assume the chance that consumption is exceeding the rated supply at intervals.

Is it a good, bad, or neutral sign that the PSUs 12-volt rail is outputting at present 18.82 volts measured by a VOM

The 12-Volt supply should be regulated, so why does it produce 19 volts?

two Nvidia Geforce 570 GTX display cards, which both erratically varied between 22 and 55 Amps (at only 1 volt

Is this normal?  55 amps is a huge amount of current, so I wonder if this is the source of your overload.  

... Thinkpads_User
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garycaseCommented:
First, there's no 1v rail in the PSU, so your comment r.e. "... varied between 22 and 55 Amps (at only 1 volt) ..."  doesn't make sense.      How did you determine this power draw was at 1v?

Second, a 12v rail should be within 5% of 12v -- NOT anywhere near 18v.    That's so far out of spec it could easily damage your PC.     Are you sure you're measuring this correctly??

I'd tet a PSU tester and confirm that your power supply rails are providing the proper voltages.
http://www.newegg.com/Product/Product.aspx?Item=N82E16899705003

... also, do your power supplies have single or multiple 12v rails?    If multiple, are you sure you're using different rails for the two different cards?     Otherwise you could easily overload the PSU ... which could account for your failures.
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John HurstBusiness Consultant (Owner)Commented:
Another thing that could cause issue is a mis-formed bus socket or mis-formed card plug that is causing a false current path.  ... Thinkpads_User
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Michael-BestCommented:
You my have a supply issue.
Have you checked the AC power supply is stable & of constant voltage?
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John HurstBusiness Consultant (Owner)Commented:
Four different supplies have been used. That would seem to rule out a supply-only issue. The way the supply is connected in is more likely, I think.
...  Thinkpads_User
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Dave BaldwinFixer of ProblemsCommented:
Heat and a lack of airflow are the things that usually cause power supply failures.  A 1050 W power supply can fail at 10% load if it does not get any airflow to carry away the heat.  At over 600 Watt load, you should have a lot of hot air coming out somewhere!!

I think you have other issues also is the measurements you have made are correct.
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Michael-BestCommented:
Clarification of ID: 38379732:

Have you checked the "mains" AC power supply is stable & of constant voltage?
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nobusCommented:
>>  PSUs 12-volt rail is outputting at present 18.82 volts measured by a VOM <<   that looks like you are measuring from 5V to 12 V = 17 V output
are you sure you measure the 12 V? between the YELLOW and black wire on the molex?

if it IS 18V, then you can repalce the motherboard, and many parts - they will be damaged

as to answer your Q - why are they failing - i would say - if they are installed correct, the cause lies outside the PC
so have the AC and grounding checked !
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CElliott2Author Commented:
Thank you GaryCase for yur answer.  In response to your questions:
"First, there's no 1v rail in the PSU, so your comment r.e. "... varied between 22 and 55 Amps (at only 1 volt) ..."  doesn't make sense.      How did you determine this power draw was at 1v?"

GPU-Z 0.6.4 says "VDDC" is 0.943-0.951 V. It also says that VDDC Current varies now between 28.0 and 57.5 A (not ma).

"Second, a 12v rail should be within 5% of 12v -- NOT anywhere near 18v.    That's so far out of spec it could easily damage your PC.     Are you sure you're measuring this correctly??"

NO!  Those measurements were taken with a digital VOM I received as part of a computer electronics course.  The company has since gone out of business.  Using an expensive Radio Shack "Micronta" digital VOM the 12V hard disk supply is generally solid at 12.41 V, but it dips down to 10.5 to 11.5 V occasionally, and down to 8.56 V much more rarely.

Your suggestion to purchase a decent PSU tester is a good one; thanks again.

The TX 850 has only one 12V rail, but that is true of all of Corsair's 850 W PSUs, even the most expensive.

The voltage at the wall socket varies between 114.8 and 117.1, but it is pretty steady between 116 and 117.
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CElliott2Author Commented:
Thank you Michael-Best for your answer.
"You my have a supply issue.
Have you checked the AC power supply is stable & of constant voltage?"

Yes, the voltage at the wall socket varies between 114.8 and 117.1, but it is pretty steady between 116 and 117.
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CElliott2Author Commented:
Thanks Dave Baldwin for your answer.

"Heat and a lack of airflow are the things that usually cause power supply failures."

So true!  But here I have a humongous Honeywell floor fan (purchased at www.kaz.com at a great price, BTW) that blows across the whole rig, which sits w/o case on my work table.  Plenty of hot air comes out of everything, the CPU cooler, the display cards, and the PSU.
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John HurstBusiness Consultant (Owner)Commented:
If the power supply is decent and is properly filtered, then the particular DVM should not matter. I use B&K Precision and ExTech DVM's for electronic work. Neither are cheap, but they are both very reliable if you are looking for something better.

I assumed your AC supply was fine and you have verified that. You have used 4 PSU's, so the motherboard and/or connecters are definitely looking bad.

.... Thinkapds_User
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CElliott2Author Commented:
Reply to nobus and thinkpad_user: Thanks for your comments.

"Four different supplies have been used. That would seem to rule out a supply-only issue. The way the supply is connected in is more likely, I think."

The house current is OK.  It is correctly gounded and the voltage at the wall socket only varies between 114.8 and 117.1, but it is pretty steady between 116 and 117.

However, all the current goes thru a UPS, which claims to output a pseudo-sine wave when on battery power, which almost never happens in Center City Philadelphia.  I checked the UPS output when not on battery power with an oscilloscope just now, and the output wave form is no different between when the leads are connected to the UPS and when they are connected to the wall socket.  Moreover, the frequency is correct: about 17 ms between wave peaks.  However, I have read that some UPS's can wreak a PSU with automatic power factor correction, which mine all have had, if the UPS does not output a true sine wave.  I told the PSU manufacturer about the UPS, but it never commented in reply.  Could this be my problem?
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John HurstBusiness Consultant (Owner)Commented:
If you have a true UPS, it should put out near-enough a sine wave not to cause problems. If the UPS is low-grade consumer quality, the output may have a lot of harmonics. The only way to tell is with a decent oscilloscope or a True-RMS DVM. The former will display harmonics, the latter will give you the true effective voltage. It the true effective voltage is 115-120 Volts AC then it is not the problem.

I have a Smart UPS 750XL and it keeps my network plus my desktop Thinkcenter running 7x24, has done for years and does not cause issues.

 Could this be my problem?    

Only if, as I noted, you have an ugly square wave output or output with a high level of harmonics (nearly the same thing) . The important thing is the True RMS voltage which your DVM probably does not do. Mine do not and True RMS DVM's are generally very expensive (Fluke or high-end B&K).  Low levels of harmonics are generally no problem.

.... Thinkpads_User
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John HurstBusiness Consultant (Owner)Commented:
Here for reference is the output of an APC Smart UPS 750XL.  You can see a small level of harmonic distortion top and bottom (at least I can), but it is nothing at all significant and does not cause any issue with my gear.

SineWave with distortion
.... Thinkpads_User
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nobusCommented:
well - if all PSU are failing, the first suspect is the UPS
you can also test by connecting the UPS to another AC rail in the house (to verify that is not the cause - eg, bad contacts)
also, for checking AC waveforms, and UPS, you shoud have a power monitor, since the scope only records a moments value
see :  http://www.fluke.com/fluke/uken/solutions/pq/default.htm
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Michael-BestCommented:
"The house current is OK.  It is correctly gounded and the voltage at the wall socket only varies between 114.8 and 117.1, but it is pretty steady between 116 and 117."

This may not be the case over a long period...you may have spikes or lows under certain conditions.
If this is the case it will be hard to trace, but your UPS Voltage regulator is probably the cause.

It may be simpler to just replace the UPS and see if the problem is solved by that.
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John HurstBusiness Consultant (Owner)Commented:
@CElliott2  - I thnk it might have been more reasonable for you to split points on this answer.

.... Thinkpads_User
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CElliott2Author Commented:
That is what I thought I did.  I clicked on accept multiple solutions, and once I had done that, the system would not let me change anythng.  If I didn't give everyone points,  I screwed up.  Sorry.

In any case, thanks for your help!
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CElliott2Author Commented:
So, how do I distribute points to multiple experts?
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John HurstBusiness Consultant (Owner)Commented:
When you on this screen here, there is a choice: Accept Multiple Solutions and Accept as Solution on each answer post. This is on this screen here where you will see these two options. Click on Accept Multiple Solutions here and then you will be led to a screen where you can distribute points.

.... Thinkpads_User
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CElliott2Author Commented:
I marked the best soln as the one that suggested that I check all the voltages coming out of and running into the PSU.  That was the most practical and time-consumming suggestion for failing PSUs.  I only run PSUs between 1/2 and 3/4 of full load, as that is their most efficient operating range (see the PSU efficiency chart on Corsair's website, which I cannot find now), so overloading should not be the answer.  That heat is the nemesis of all electronic equipment was an excellant reminder.

I marked the soln as good rather than excellant because no one said, "Here are the causes of PSU failure, pick yours!"  Just to be pedantic, a know-it-all, and a pain in the A**, here is what I think is a good solution:

The major causes of PSU failure, somewhat in order of occurance, are:
Overheating
Overloading due to insufficient capacity for equipment connected
Power surges
Dust & dirt
Faulty connections or equipment (e.g., mobo or hard disk failure)
Physical shock
Improper electrical supply current
(sources: results of a Bing search on "Major causes of power supply failure")
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nobusCommented:
imo - it's not quite correct
while overheating iS a major issue (if trespassing the max temp of components) it is the heating up/cooling down cycle that causes most problems, by crimping expanding the solderings, and different materials in a different way

also - tyou never answered my question about the 17V measured :  are you sure you measure the 12 V? between the YELLOW and black wire on the molex?
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