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Desktop computer PSU specs; possible to DIY?

post #1 of 26
5/18/10 at 6:04pm
Thread Starter 

Back when I RMA'd my desktop power supply, I got back a sheet showing some load voltages/current/etc. I thought I share with everyone...

 

PC Power & Cooling Silencer PPCS500 500W
Rated for +3.3V@24A,+5V@24A,+12V@35A,-12V@0.8A,+5VSB@2.5A

+12V Load       +12V       -12V      +3.3V      +5V        +5VSB
Load Current    34.00 A     0.50 A    8.000 A   10.000 A   2.000 A
Upper range     12.60 V   -13.00 V    3.465 V    5.500 V   5.250 V
Lower range     11.40 V   -11.00 V    3.135 V    4.750 V   4.750 V
Outcome         11.91 V   -11.71 V    3.260 V    4.900 V   4.850 V
Wattage         404.9 W     5.86 W   26.100 W   49.000 W   9.700 W
Total Wattage   495.6 W

+5V Load       +12V       -12V      +3.3V      +5V         +5VSB
Load Current    30.00 A     0.50 A    9.000 A   20.000 A   2.000 A
Upper range     12.60 V   -13.00 V    3.465 V    5.500 V   5.250 V
Lower range     11.40 V   -11.00 V    3.135 V    4.750 V   4.750 V
Outcome         12.19 V   -11.91 V    3.250 V    4.770 V   4.840 V
Wattage         365.7 W     5.96 W   29.300 W   95.400 W   9.680 W
Total Wattage   506.0 W

+3V Load       +12V       -12V      +3.3V      +5V         +5VSB
Load Current    30.00 A     0.50 A   20.000 A   12.000 A   2.000 A
Upper range     12.60 V   -13.00 V    3.465 V    5.500 V   5.250 V
Lower range     11.40 V   -11.00 V    3.135 V    4.750 V   4.750 V
Outcome         12.07 V   -11.81 V    3.240 V    4.840 V   4.840 V
Wattage         362.1 W     5.91 W   64.800 W   58.100 W   9.680 W
Total Wattage   500.6 W

Burn in         +12V       -12V      +3.3V      +5V         +5VSB
Load Current    30.00 A     0.50 A   12.000 A   15.000 A   2.000 A
Upper range     12.60 V   -13.00 V    3.465 V    5.500 V   5.250 V
Lower range     11.40 V   -11.00 V    3.135 V    4.750 V   4.750 V
Outcome         12.03 V   -11.85 V    3.260 V    4.840 V   4.840 V
Wattage         372.9 W     5.92 W   39.100 W   72.600 W   9.680 W
Total Wattage   500.3 W

 

For a PSU that can supply this much current, linear PSU's are out of the question. There are linear PSU's out there like the PicoPSU, but it probably won't be able to power high-end systems.

 

My criteria is a PSU that is silent (which is why I RMA'd my PSU in the first place... piercing coil whine) and is able to supply relatively high current in the +12V rail and +5V rail. I don't really know what uses the 3.3V rail.

 

Any starters on how we can design an audiophile desktop PSU?

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post #2 of 26
5/18/10 at 9:40pm

I believe the CPU runs off the 3.3V rail (regulated down), as well as the RAM, seeing as how both are usually under 3.3V. Possibly more.


Edited by Juaquin - 5/19/10 at 2:41am
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post #3 of 26
5/19/10 at 11:25am

Quote:

Originally Posted by Juaquin View Post

I believe the CPU runs off the 3.3V rail (regulated down), as well as the RAM, seeing as how both are usually under 3.3V. Possibly more.

Not a speculation without merit, but the CPU runs off of the 12V rail. Not sure about RAM.

 

If OP wanted something quiet, a Seasonic or Seasonic-built unit would have done the job. Or one of the fanless designs floating around.

 

If you want to build your own, I hope you know a source for big honkin heatsinks. Other than that, I can't help you. If you ever do get it to work well, send it in to Jonnyguru. That'll get you famous, quick like (if it's good, anyways).

 

(You get bonus points if you use Nichicon KZs for everything)
 

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post #4 of 26
5/19/10 at 11:43am

You will probably find it easier to modify a commercial unit that to build your own thing, especially if you are looking for that much power and something that will fit in a standard slot.

 

A popular tweak for combating inductor noise (the whine you describe) is to DIY-pot the inductors, although most people dont get the rest of their systems quiet enough to benefit from this: you should be proud that you heard it over the fans and HDD's

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post #5 of 26
5/19/10 at 12:07pm

http://www.silentpcreview.com/article986-page1.html

http://www.silentpcreview.com/Enermax_Modu87_500W

they're pricy, but they're probably the best for what you're looking for

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post #6 of 26
5/19/10 at 12:18pm
Quote:
Originally Posted by Ntropic View Post

 

Not a speculation without merit, but the CPU runs off of the 12V rail. Not sure about RAM.

 


Hmm,  Intel is stating that the Voltages are more like 1.4 on the i7's:

 

pg 68: http://download.intel.com/design/processor/datashts/322164.pdf

 

 

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post #7 of 26
5/19/10 at 1:33pm

Quote:

Originally Posted by cobaltmute View Post


 

 

Power is still drawn from the 12V rail, and then downed to 1-1.5v, or whatever the processor wants.
 


Edited by Ntropic - 5/19/10 at 6:33pm
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post #8 of 26
5/19/10 at 1:43pm
Quote:
Originally Posted by Ntropic View Post
Power is still drawn from the 12V rail, and then downed to 1-1.5v, or whatever the processor wants.

 


That's quite a big drop, especially considering the CPU in a desktop can draw a lot of current (hence my assumption that it was drawn from 3.3V). Out of curiosity, why do they regulate from 12V, and what is the 3.3V used for then?

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post #9 of 26
5/19/10 at 1:59pm
Thread Starter 

PCI and PCI Express cards can use all three rails.

 

And 12.x V to 1.x V for the CPU is indeed a very big drop. The ATX connector also includes all three rails, and I still feel that the 3.3V is probably regulated down for the memory and for the CPU.

 

Edit: OK, looks like the CPU does gets its power from the 12V rail. See schematics: http://download.intel.com/design/chipsets/schematics/25281302.pdf page 84


Edited by ShinyFalcon - 5/19/10 at 7:14pm
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post #10 of 26
5/19/10 at 3:41pm

http://www.cicsmemoryplayer.com/uploads/B_Linear_PSU.jpg

 

http://www.cicsmemoryplayer.com/index.php?n=CMP.ApdxBAdvanced

 

It has already been done.


Edited by weibby - 5/19/10 at 8:42pm
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post #11 of 26
5/19/10 at 4:58pm

Quote:

Originally Posted by weibby View Post

http://www.cicsmemoryplayer.com/uploads/B_Linear_PSU.jpg

 

http://www.cicsmemoryplayer.com/index.php?n=CMP.ApdxBAdvanced

 

It has already been done.

 

 

Oh my.

 

Quote:

Originally Posted by ShinyFalcon View Post

PCI and PCI Express cards can use all three rails.

 

And 12.x V to 1.x V for the CPU is indeed a very big drop. The ATX connector also includes all three rails, and I still feel that the 3.3V is probably regulated down for the memory and for the CPU.

 

Edit: OK, looks like the CPU does gets its power from the 12V rail. See schematics: http://download.intel.com/design/chipsets/schematics/25281302.pdf page 84


Told you so.

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post #12 of 26
5/19/10 at 5:55pm

So no theories as to why they drop the 12V down so much instead of just using the 3.3V, which seems to have plenty of amperage?

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post #13 of 26
5/20/10 at 3:50am

Maybe its Google's fault?  It has been reported that their PCs have only 12V going to the board.  They regulate everything else on board as it makes for a cheaper overall unit.

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post #14 of 26
5/20/10 at 4:40am
Quote:
Originally Posted by Juaquin View Post

So no theories as to why they drop the 12V down so much instead of just using the 3.3V, which seems to have plenty of amperage?

 

 

It is more efficient, in a nut shell. The drop doesn't matter at all for SMPS's, they have very good efficiencies where it is usually more efficient to run from higher voltage inputs. The wire connecting your PSU to the board don't need to be as heavy either, as there is less current flowing for the same power delivered, and if you look at how many separate 12v wires they put in there already these days, then you need to multiply that by 4 for what would be required for 3.3v supply.

 

Don't think that if you put a linear power supply in a computer that you'll make it electrically quieter, everything in your computer is made of digital gates switching at all sorts of frequencies spewing out more garbage back into the power supply that what a good SMPS is doing in the first place. If you really care, just filter the sensitive circuits that you want like everyone else


Edited by DaKi][er - 5/20/10 at 9:42am
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post #15 of 26
5/20/10 at 5:44pm
Quote:
Originally Posted by DaKi][er View Post

It is more efficient, in a nut shell. The drop doesn't matter at all for SMPS's, they have very good efficiencies where it is usually more efficient to run from higher voltage inputs. The wire connecting your PSU to the board don't need to be as heavy either, as there is less current flowing for the same power delivered, and if you look at how many separate 12v wires they put in there already these days, then you need to multiply that by 4 for what would be required for 3.3v supply.


Thanks for the answer. So the motherboard has an onboard SMPS to convert 12V to 3.3V? I figured it would be a simple linear regulator, in which case you'd be wasting a ton of heat. It does make sense not to run the extra 3.3V cables if it can be avoided, but why supply 3.3V in the first place then?

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