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Bombastinator

Some questions about voltage rails that are dumber than I wish they were.

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Posted · Original PosterOP

I’m an old gamer.  I’ve built PCs since the days of coppermine, but I haven’t built a new PC in a while.  The intel core stuff things just stopped getting better quickly, and if it ain’t broke don’t fix it.  My mobo is z97.

 

i was trying to help some guy build a PC and I am seeing my knowledge is more dated than even I thought.  I was reading pinned posts on this subforum, and they talked about the 12v rail a good bit, but the use of a 5v rail was not described other than that they can exist.  I’m noticing  some newer PSUs don’t even have 5v rails anymore.  


USB is 5v.  Does it even run on the 5v rail or is there just some kind of voltage step down?  Is it in the PSU or the mobo?  

 

Is there still any use for a 5v rail anymore?  What was it used for originally?

 

Warranties for newer PSUs seem to vary widely and are sometimes double what I remember the standard safe life expectancy of a PSU to be, which was 4-5 years for a good one.  Less to much less for a not so good one.  Has the tech changed or is this just a marketing thing?


Life is like a bowl of chocolates: there are all these little crinkly paper cups everywhere.

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15 minutes ago, Bombastinator said:

I’m an old gamer.  I’ve built PCs since the days of coppermine, but I haven’t built a new PC in a while.  The intel core stuff things just stopped getting better quickly, and if it ain’t broke don’t fix it.  My mobo is z97.

 

i was trying to help some guy build a PC and I am seeing my knowledge is more dated than even I thought.  I was reading pinned posts on this subforum, and they talked about the 12v rail a good bit, but the use of a 5v rail was not described other than that they can exist.  I’m noticing  some newer PSUs don’t even have 5v rails anymore.  


USB is 5v.  Does it even run on the 5v rail or is there just some kind of voltage step down?  Is it in the PSU or the mobo?  

 

Is there still any use for a 5v rail anymore?  What was it used for originally?

 

Warranties for newer PSUs seem to vary widely and are sometimes double what I remember the standard safe life expectancy of a PSU to be, which was 4-5 years for a good one.  Less to much less for a not so good one.  Has the tech changed or is this just a marketing thing?

12v is used to power pretty much everything on your PC. 5v isn't used as much anymore. I believe it's just used for USB and storage devices.

5v will be found on a good modern ATX PSU. Same with 3.3v, which is even less used. 


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Posted · Original PosterOP
1 hour ago, PSUGuru said:

12v is used to power pretty much everything on your PC. 5v isn't used as much anymore. I believe it's just used for USB and storage devices.

5v will be found on a good modern ATX PSU. Same with 3.3v, which is even less used. 

Everything has USB and storage though.  Those 12v only PSUs still function so there’s got to be some work around.  Possibly a crappy one.


Life is like a bowl of chocolates: there are all these little crinkly paper cups everywhere.

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All ATX PSUs still have a 5V output, because the ATX specification still requires 12V, 5V, 3.3V, 5VSB and -12V.

 

There are some computers by companies like Dell or HP that use custom motherboards, custom PSUs and custom construction overall. They sometimes have power supplies with only 12V, and they convert it to lesser voltages with DC-DC converters on the motherboard. Again, those PSUs, motherboards and computers overall are completely proprietary and don't follow the ATX standard. Just like your laptop's power supply doesn't have 12V/5V/etc, instead it has only one 19V volt rail or so.

 

Intel is working towards a 12V-only ATX specification, since it's better for many reasons to need just one voltage rather than multiple ones.

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Posted · Original PosterOP
12 minutes ago, OrionFOTL said:

All ATX PSUs still have a 5V output, because the ATX specification still requires 12V, 5V, 3.3V, 5VSB and -12V.

 

There are some computers by companies like Dell or HP that use custom motherboards, custom PSUs and custom construction overall. They sometimes have power supplies with only 12V, and they convert it to lesser voltages with DC-DC converters on the motherboard. Again, those PSUs, motherboards and computers overall are completely proprietary and don't follow the ATX standard. Just like your laptop's power supply doesn't have 12V/5V/etc, instead it has only one 19V volt rail or so.

 

Intel is working towards a 12V-only ATX specification, since it's better for many reasons to need just one voltage rather than multiple ones.

Hmmm..  I vaguely remember some reviews saying one PSU or another lacked a 5v rail.  The post above says many lack 3.3v rails.  Not sure what the 3.3v is for or what 5VSB even is.

 

Google for me it sounds like.  *sigh*. Sometimes I wonder how I lived without search engines.  Or cell phones.

UPDATE:

ooh! 5VSB is always on standby power.  Can’t even switch it off.  Got to unplug the thing.  Never knew that.  Explains by constantly dying UPSes though.  I was blaming it on my house.


Life is like a bowl of chocolates: there are all these little crinkly paper cups everywhere.

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29 minutes ago, Bombastinator said:

The post above says many lack 3.3v rails.

That's wrong - all ATX PSUs have 3.3V rails, and 5V rails as well. Phrasing it as "5v will be found on a good modern ATX PSU" is really very weird, because all ATX PSUs have 5v: good, bad, modern, and old. Not just good modern ones...

If a PSU doesn't have 12V, 5V, 3.3V, -12V, and 5VSB outputs, then it isn't an ATX PSU, and you wouldn't be able to use it to build a custom PC.

Like I said, some prebuilt manufacturers, who manufacture their own cases and motherboards, have the privilege to design their own PSUs too, and they can have any shape and output whatever voltages they want. The end components still have to receive 12V, 5V and 3.3V from somewhere, so if the manufacturer's custom PSU doesn't output one of those voltages, then their custom motherboard does it.

 

29 minutes ago, Bombastinator said:

Hmmm..  I vaguely remember some reviews saying one PSU or another lacked a 5v rail.

Are you sure you didn't confuse it for the -5V rail? That was removed from the ATX standard in 2002.

 

29 minutes ago, Bombastinator said:

ooh! 5VSB is always on standby power.  Can’t even switch it off.  Got to unplug the thing.

It is standby power, but it's better not to unplug your PSU - the standby power keeps the primary capacitors charged, so there's less inrush current coming from your socket when you plug it back on. It's most likely not the cause of your dying UPSes, because the power consumption of a standby PSU is less than 1W, typically less than 0.5W. (If you aren't charging your phone off the USB while it's off, or something similar.)

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Posted · Original PosterOP
7 minutes ago, OrionFOTL said:

That's wrong - all ATX PSUs have 3.3V rails, and 5V rails as well. Phrasing it as "5v will be found on a good modern ATX PSU" is really very weird, because all ATX PSUs have 5v: good, bad, modern, and old. Not just good modern ones...

If a PSU doesn't have 12V, 5V, 3.3V, -12V, and 5VSB outputs, then it isn't an ATX PSU, and you wouldn't be able to use it to build a custom PC.

Like I said, some prebuilt manufacturers, who manufacture their own cases and motherboards, have the privilege to design their own PSUs too, and they can have any shape and output whatever voltages they want. The end components still have to receive 12V, 5V and 3.3V from somewhere, so if the manufacturer's custom PSU doesn't output one of those voltages, then their custom motherboard does it.

 

Are you sure you didn't confuse it for the -5V rail? That was removed from the ATX standard in 2002.

 

It is standby power, but it's better not to unplug your PSU - the standby power keeps the primary capacitors charged, so there's less inrush current coming from your socket when you plug it back on. It's most likely not the cause of your dying UPSes, because the power consumption of a standby PSU is less than 1W, typically less than 0.5W. (If you aren't charging your phone off the USB while it's off, or something similar.)

It does if I was assuming there was zero power draw.  even a tiny draw will wear a battery.


Life is like a bowl of chocolates: there are all these little crinkly paper cups everywhere.

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