voltage rails - which is most impt 3.3/5/12?

[Wigwam]

i have an enermax eg365 psu
i note that the +5 and +12 v rails are rock stable at +4.95 and +11.95 respectively.
the +3.3v fluctuates between +3.28 and +3.38v

what are the ramifications of this? which rail does cpu power depend on and what does the +3.3 rail control?

 

[myocardia]

Where your cpu's power comes from depends on whether you have an AMD-based system or a P4-based system. The AMD's (all of them), derive their power from the 5v rail. The Intel's (all of them), derive their cpu power from the 12v rail. And voltage fluctuations that small affect nothing, ever. Enermax's are good psu's, and are great for overclocking P4's, because of their strong 12v rails.

 

[Wigwam]

Hi Myocardia.
Thanks

It is a 2100+ based AMD system. thanks for the reassurance. I got some "advice that" the fluctuations reflect my psu maxign out which may affect my o/c ability yada yada yada...it didnt somehow ring true to me but nice to clarify.

so what does the 3.3 rail control then?

as to the psu...yes power-wise it is nice but it doesnt like my particular setup cos it causes "something" to emit a high pitched whine; my old psu didnt and this doesnt when swapped out to other machines

 

[Acanthus]

To check PSU stability you can watch an MBM while the system is under load, you can use applications like 3dmark 2001 in a loop with a motherboard monitor running, then just check the graphs after a few minutes.

Small fluctuations are normal, but a sag of more than 5% below rating is bad.

On a side note i belive that power supply has internal adjustible pots if you read up on it. You can stabilize lower voltages by tweaking the pots.

 

[Avalon]

I believe the 3.3v rail is for memory

 

[Viperoni]

Originally posted by: myocardia
Where your cpu's power comes from depends on whether you have an AMD-based system or a P4-based system. The AMD's (all of them), derive their power from the 5v rail. The Intel's (all of them), derive their cpu power from the 12v rail. And voltage fluctuations that small affect nothing, ever. Enermax's are good psu's, and are great for overclocking P4's, because of their strong 12v rails.

This is incorrect.
Many newer Nforce2 boards have switched to powering the CPU from the +12v line, except Asus.
You can easily tell such boards by the presence of a +12v PS connector.

Generally the stabler the voltage supply the better, without exception. I believe Crucial said that shaky power supplies cause ram to burn up a lot quicker than good PS's.

 

[Wigwam]

well it is an asus m/b so the 5v supply to cpu still applies to me.

 

[Zebo]

Save yourself the trouble of "guessing" and get a enermax 460+ with strong rails across the board. I had a Brand new "true 480" from antec and it was unstable then caught fire after blowing a cap!!! then I swap to enermax no problems since. This "True" was running only the following and craped out initailly running benches before totally going out.

2x raptors
2xcd/dvd
barton at 1.9Vcore
mobo
512 MB ram @ 2.7V
9800pro card at default Volts
and 5 case fans using about 3A off the 12.

it destoryed my mobo and vid card and I belive now one of my drives clicks..could be a bad sign.

 

[Margalus]

Don't listen to the people who say amd's get their power from 5v, that is not true at all. 12v is one of the most important. As that is where BOTH amd and intel draw 100% of the cpu's power from. amd boards just generally don't have the extra 12v lead that intel specified.

 

[GenAris]

I think the 3.3/5V rail is the most important for the CPU instead the 12V. Note that the ATX 2.03 PSUs have two independent rails of 12V (in theory): one of them is mostly used for Hard Disks' and CD-ROM's motors, and the another is for the CPU.

The 3.3/5V rail is used for the drives' logic, chipset and memory chips, and for power the CPU also. So I checked the power for this lane if I had a 'power-eating' system with a lot of cards, and the CPU 12V too if I wanted to overclock it.

I hope you understand me... My English is too poor

 

[Margalus]

Originally posted by: GenAris
I think the 3.3/5V rail is the most important for the CPU instead the 12V.
I hope you understand me... My English is too poor

your english is fine. It is just your information which is poor

the cpu has absolutely nothing to do with either the 3.3v or 5v anymore. The pentium 3's and k6's were the last cpu's to use the 5v rail for the cpu. the athlons and p4's switched to the 12v rail exclusively. the 3.3v is used for the motherboard chipset, ram, agp and pci. the 5v is used for the pci, harddrives, cdroms and usb. 12v is used for the cpu, harddrives, cdroms, and fans.

 

[TerryMathews]

Originally posted by: Margalus

Originally posted by: GenAris

I think the 3.3/5V rail is the most important for the CPU instead the 12V.

I hope you understand me... My English is too poor

your english is fine. It is just your information which is poor



the cpu has absolutely nothing to do with either the 3.3v or 5v anymore. The pentium 3's and k6's were the last cpu's to use the 5v rail for the cpu. the athlons and p4's switched to the 12v rail exclusively. the 3.3v is used for the motherboard chipset, ram, agp and pci. the 5v is used for the pci, harddrives, cdroms and usb. 12v is used for the cpu, harddrives, cdroms, and fans.

Yours isn't top-notch either. The processor has nothing to do with where it gets it's power; the motherboard does all the leg-work. You can't make a blanket statement like that.

I will grant you that most boards these days derrive Vcpu from the 12V line, but there are some boards that don't. ASUS, in specific, seems to like that old 5V rail. Heck, their dual Athlon board (A7M266-D) had one processor powered from 5V and the other from 12V. Was nice because you could run the system on a 300W power supply.

 

[Duvie]

I concur with Terry....Up until recent many amd cpu systems were based on the 3.3v and 5v rails, hence the recommendation of amd approved power supplies tended to have higher combined output wattage on those rails then a p4 approved one...

As far as I know the 3.3v rail with my system is important for Ram....However the 3.38 to 3.28 is not a big flux and well within the 5% plus or minus tolerance. You should have nothing to worry about there....

I have built amd systems in the 2.3ghz range with quality 300-350watt PSU....I think quality is the key here. I don't mind paying a bit more for antec or enermax to know that I am getting quality. With enermax I get the highest amps on the 12v of any similar wattage power supply I have seen....My 12v as all of them are tight at idle near or at the actual rail voltage. Under fluctuation to heavy load I see 1-1.5% drops and that is a good sign since I am running a heavily oc'd system with power hungry vid card, 4 drives, 5 case fans, etc....

 

[Sokratz]

Ready, Set?, Click!

 

[gil11542]

Might want to read this, I have a 2600M OC to 2.5gig+ 1.775 volts. when I kick Prime95 my 5v rail drops from 4.9v to 4.7v (Enermax 461) So I do believe that my A7N8X DLX pulls power for the CPU from the 5v rail.



Read This Thread

 

[Kuznetsov]

Originally posted by: Wigwam
Hi Myocardia.

Thanks



It is a 2100+ based AMD system. thanks for the reassurance. I got some "advice that" the fluctuations reflect my psu maxign out which may affect my o/c ability yada yada yada...it didnt somehow ring true to me but nice to clarify.



so what does the 3.3 rail control then?



as to the psu...yes power-wise it is nice but it doesnt like my particular setup cos it causes "something" to emit a high pitched whine; my old psu didnt and this doesnt when swapped out to other machines

Yes its the combination of R9500Pro and the ASUS board that does it. I have ASUS P4P800 and 9500pro also get the same high pitch noises. CHanging the PSU will change the sound level but the sound is still there. Also tried the PSU on another machine and it was fine.

Change your graphics card and no more high pitch noise.

 

[PliotronX]

3.3v is where the CPU, mobo, and components (including vid card) receive their primary juice from. Many of today's boards utilize a secondary connection via the ATX12V 2x2 connector or in the case of vid cards, the 4-pin 12v molex connectors or floppy connectors. I would say 3.3v is the most important followed by 12v and then 5v but it's pretty crucial to have them all within 5% of the spec. Your 3.3v rail is fine. In fact the PSU may be supplying more than what you see reported from the motherboard as the power flows through the board it loses some voltage due to resistence (especially as more heat is added to the mix). At the molex connectors (as measured via multimeter), it's typically between .05 and .1 volts higher than reported by the mobo. Unless you're having stability issues, I wouldn't worry at all.

 

[Acanthus]

Voltages on my rig with adjusted truecontrol

 

[Joemonkey]

I spoke with an Asus tech support rep today, he said on the P4GEV motherboard the 3.3V rail controls the AGP slot and the CPU power...

also as extra proof the 3.3 is important, i have a bad power supply that overvolts on the 3.3 at a constant 3.64 volts. If i have a good PS plugged in, the CPU voltage is 1.52ish, with the overvolting PS the CPU voltage is 1.61ish

 

[Acanthus]

3.3 almost always powers mem as well.

 

[Wigwam]

Yes its the combination of R9500Pro and the ASUS board that does it. I have ASUS P4P800 and 9500pro also get the same high pitch noises. CHanging the PSU will change the sound level but the sound is still there. Also tried the PSU on another machine and it was fine.

Change your graphics card and no more high pitch noise.

thanks - i assume it might be some odd power-fluctuation wierdness with the psu on this setup and was cinsiderring offloading it but i guess not quite yet. mind you the sound doesnt seem to eminate from near the gfx card - infact i cant pinpoint an exact source at all!