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Why do PSUs keep having high 3.3/5v rails?

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orangat

Golden Member
Why do manufacturers still keep churning out psu's with 30A/30A on the 3.3/5v rails?
The load on both rails is probably about 6A max each on a current high end PC.

Since many devices including drives and graphics cards now load the 12v rail, wouldn't it just make sense for power supplies to beef up the 12v rail instead?
 
what do you think the processor and motherboard use? do you realize how much current the processor uses? 90watts of power at 1.5 volts is 60amps. where do you think it is drawing that from?
 
Originally posted by: Bigsm00th
what do you think the processor and motherboard use? do you realize how much current the processor uses? 90watts of power at 1.5 volts is 60amps. where do you think it is drawing that from?
Click to expand...

from the 12V line 😛 (the square quad plug next to the CPU)
 
Text


from that link:

Overall current usage limitation on the power supply should not exceed a combined system power output for the +5V and +3.3V outputs.
Click to expand...

that doesnt mean it draws all of the power from those rails, but a lot of total system power will come from those 2 rails.
 
Originally posted by: Bigsm00th
what do you think the processor and motherboard use? do you realize how much current the processor uses? 90watts of power at 1.5 volts is 60amps. where do you think it is drawing that from?
Click to expand...

The link below shows usage for each rail for 2 PCs with A64 at 2.8 and P4 at 4Ghz running benchmarks and cpuburn.
http://www.xbitlabs.com/articles/other/display/bluestorm_3.html
A paltry 3A/5A on the 5v/3.3v rail at most for the AMD system. And the Intel PC never exceeds 5A/1A.

More numbers here:-
http://www.silentpcreview.com/Sections+index-req-printpage-artid-265.html

So what about that huh??
 
Probably because it wouldn't take any less space inside the PSU to make the 5v/3.3v rails weaker, and they already have a large stock of necessary components to keep the rails as they are.
 
If a power supply manufacturer can give these rails a lot of amps, then why not? It doesn't hurt the PC to have these amps available.
 
Originally posted by: orangat
Originally posted by: Bigsm00th
what do you think the processor and motherboard use? do you realize how much current the processor uses? 90watts of power at 1.5 volts is 60amps. where do you think it is drawing that from?
Click to expand...

The link below shows usage for each rail for 2 PCs with A64 at 2.8 and P4 at 4Ghz running benchmarks and cpuburn.
http://www.xbitlabs.com/articles/other/display/bluestorm_3.html
A paltry 3A/5A on the 5v/3.3v rail at most for the AMD system. And the Intel PC never exceeds 5A/1A.

More numbers here:-
http://www.silentpcreview.com/Sections+index-req-printpage-artid-265.html

So what about that huh??
Click to expand...

i didnt realize i was taking part in some sort of e-penis comparison tournament.
 
Originally posted by: Bigsm00th
Originally posted by: orangat
Originally posted by: Bigsm00th
what do you think the processor and motherboard use? do you realize how much current the processor uses? 90watts of power at 1.5 volts is 60amps. where do you think it is drawing that from?
Click to expand...

The link below shows usage for each rail for 2 PCs with A64 at 2.8 and P4 at 4Ghz running benchmarks and cpuburn.
http://www.xbitlabs.com/articles/other/display/bluestorm_3.html
A paltry 3A/5A on the 5v/3.3v rail at most for the AMD system. And the Intel PC never exceeds 5A/1A.

More numbers here:-
http://www.silentpcreview.com/Sections+index-req-printpage-artid-265.html

So what about that huh??
Click to expand...

i didnt realize i was taking part in some sort of e-penis comparison tournament.
Click to expand...

e-peni? I posted real numbers and you have nothing but your own opinion that 3.3/5v are sooo important. Give real information instead of useless sarcasm.
 
Originally posted by: orangat
Originally posted by: Bigsm00th
Originally posted by: orangat
Originally posted by: Bigsm00th
what do you think the processor and motherboard use? do you realize how much current the processor uses? 90watts of power at 1.5 volts is 60amps. where do you think it is drawing that from?
Click to expand...

The link below shows usage for each rail for 2 PCs with A64 at 2.8 and P4 at 4Ghz running benchmarks and cpuburn.
http://www.xbitlabs.com/articles/other/display/bluestorm_3.html
A paltry 3A/5A on the 5v/3.3v rail at most for the AMD system. And the Intel PC never exceeds 5A/1A.

More numbers here:-
http://www.silentpcreview.com/Sections+index-req-printpage-artid-265.html

So what about that huh??
Click to expand...

i didnt realize i was taking part in some sort of e-penis comparison tournament.
Click to expand...

e-peni? I posted real numbers and you have nothing but your own opinion that 3.3/5v are sooo important. Give real information instead of useless sarcasm.
Click to expand...

:roll: whatever you say buddy. this would be worth my time if you werent such a moron.
 
Would it be better for mobos to begin using the 3.3V or 5V rails for processor power? Judging by the amount of heat dissipated by the power transistors on most mainboards, the losses during convertion from 12V --> VCPU seem to be significant. Would converting 3.3V --> VCPU be less wastful?

 
Because backwards compatibility is important, good and probably not a huge issue for the power supply manufacturer.

Who knows when you might need a power supply for an AXP that pulls most of the CPU power from the 5v and 3.3v? The fact that these boards existed at all makes it a virtual requirement for PSU MFRs.

The bigger question is:
Why do you care so much that power supplies have such high 5v/3.3v rail power allowances?

I mean if you look at the specs on the side, most supplies will not reach full 12v capacity if the 3v and 5v rails are maxed. They 'borrow' capacity from one another such that if you have a computer that used 5v, that rail can be high, but that lowers what can be output on the 12v and 3.3v rails, or if you need 12v that can be high, but the 5v and 3.3v capabilities are reduced because of it. It doesn't really matter all that much does it?
 
Concillian,
If you are right and all rails 'borrow' capacity from each other then I suppose it doesn't matter
I think AXPs already draw most of their power from 12v.
 
I would love to see what amps my machine is pulling on the 3.3V and 5V lines... hehehehehe. That would be awesome.
 
Originally posted by: JohnAn2112
If a power supply manufacturer can give these rails a lot of amps, then why not? It doesn't hurt the PC to have these amps available.
Click to expand...
It's just marketing. Having more amps on the 3.3/5v rails pumps up the *total* power of the PSU, meaning you can advertise a big number for the total power of your cheap-o unit. Those POS 500W power supplies have really weak 12V rails, like 17-18A. That's the same as my Seasonic SS300!
 
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