12V Rails, probably a silly question

[PineyCreek]

When I knew less than nothing about computer components, I got my friends to help me pick out computer parts.  The more tech-savvy of them always tried to steer me towards PSUs that he said had multiple 12V rails in order to separate power to avoid drops on any one given rail, adversely affecting other components on that rail (ex, CPU on one, GPUs on the other, that sort of thing).  My question is, does this matter these days, and if so, how?  Also, how can you tell if your PSU has multiple separate 12V rails.  For example, I have a Corsair RM850x driving a Ryzen system with a 1080Ti.  Are PCI-E 6 and 8 pin plugs on a different rail than the 24 pin connector, etc.?

 

This seems like it should be basic knowledge so I'm trying to learn it so I don't feel like an idiot these days >_>

[seon123]

For most PSUs, look at the label. If they have multiple 12V rails listed there, they're generally multi rail. Your RM850x is single rail only.

Most high end PSUs are single rail (because clueless consumers want that), but some are configurable. Some Corsair PSUs allow you to choose in software, and some be quiet PSUs have a thing to choose single or multi rail. 

A decent multi rail PSU is preferred over an equivalent single rail PSU, especially for higher wattage PSUs. The main benefit is that they reduce the danger if something goes wrong

[PineyCreek]

1 minute ago, seon123 said:

For most PSUs, look at the label. If they have multiple 12V rails listed there, they're generally multi rail. Your RM850x is single rail only.

Most high end PSUs are single rail (because clueless consumers want that), but some are configurable. Some Corsair PSUs allow you to choose in software, and some be quiet PSUs have a thing to choose single or multi rail. 

A decent multi rail PSU is preferred over an equivalent single rail PSU, especially for higher wattage PSUs. The main benefit is that they reduce the danger if something goes wrong

Ah, good to know.  That must have been what the fuss was about with the Corsair RMi series.

 

Even so, so multi-rail is good because if something bad happens on one rail it limits the issues to whatever's on that rail then? Hrm.  Well ok.  I'm not thinking that I need to rush out and buy a replacement PSU though, but at least I'm armed with more information for future purchases.

[Stefan Payne]

33 minutes ago, PineyCreek said:

 My question is, does this matter these days, and if so, how? 

Yes

because Multiple +12V Rails is the same as your Breaker Box in your House.

 

The reason for that is to reduce the current and possible damage to components in an overload case.
Sadly these days PSU have rather high OCP but there is nothing you can do about that, thanks to the shitty power Saving Implementation of modern Graphics cards.

 

However, its still better than single Rail, if more than two and implemented correctly.

That means it works, if you have to think about the Rail Distribution of  a PSU, the manufacturer messed up and didn't use enough rails or so.

 

33 minutes ago, PineyCreek said:

Also, how can you tell if your PSU has multiple separate 12V rails. 

The manufacturer usually specifys that in the documentation of the PSU.

Not necessarily on the Label because that might confuse the Audience...

 

There are some fairy tales about Multi Rail being bad on the Internets so a Manufacturer has to do that...

 

33 minutes ago, PineyCreek said:

For example, I have a Corsair RM850x driving a Ryzen system with a 1080Ti.  Are PCI-E 6 and 8 pin plugs on a different rail than the 24 pin connector, etc.?

Ähm, for what an 850W unit with a Ryzen?!
If you want something better, get something better like a HX750, but not more watt.

You don't get any benefit of more wattage at all...

 

 

As for rail distribution:

Yes, 24pin is on a different rail than the CPU/GPU Connectors and shares a Rail with the Drive connectors. 
The Rest depends on the PSU.

As for me:
I prefer Multi Rail (=3 or more rails), though with modern implementation it only has an advantage at ~700W or more.

[PineyCreek]

16 minutes ago, Stefan Payne said:

Ähm, for what an 850W unit with a Ryzen?!

If you want something better, get something better like a HX750, but not more watt.

You don't get any benefit of more wattage at all...

I bought the RM850x new at a super cheap price on sale, which is why I had it.  Also thought at some point I might have a second video card in the system.  At that point I hadn't even decided on getting a Ryzen build, just that I might want two video cards.

[OrionFOTL]

1 hour ago, PineyCreek said:

The more tech-savvy of them always tried to steer me towards PSUs that he said had multiple 12V rails in order to separate power to avoid drops on any one given rail,

Your friend is totally talking out of his ass by the way, multiple 12V rails don't do that. Their function is exactly what the others here explained. 

[PineyCreek]

4 minutes ago, OrionFOTL said:

Your friend is totally talking out of his ass by the way, multiple 12V rails don't do that. Their function is exactly what the others here explained. 

Well, he was stating that power drops on one rail (high power draw from a device attached to the rail) wouldn't affect anything on a separate rail.  In that at least, he was correct.  It could also just be my recollection...It was 15+ years ago.

[OrionFOTL]

What are "power drops caused by high power draw"? Don't you mean voltage drops caused by high power draw? In this case multiple rails don't change anything. They all come from the same source, except in some unicorn platforms like CWT PUC inside the (2009?) Corsair HX1000 80+ White. 

[PineyCreek]

Just now, OrionFOTL said:

What are "power drops caused by high power draw"? Don't you mean voltage drops caused by high power draw? In this case multiple rails don't change anything. They all come from the same source, except in some unicorn platforms like CWT PUC inside the (2009?) Corsair HX1000 80+ White. 

Mmm...it was a long time ago, but I think what he was getting at is if you have a peripheral that draws in such a way against the rail (again, these were PSUs 15 years ago) that other peripherals serially along the 12V rail couldn't receive 12V within a certain error of margin.

[Stefan Payne]

19 minutes ago, PineyCreek said:

Mmm...it was a long time ago, but I think what he was getting at is if you have a peripheral that draws in such a way against the rail (again, these were PSUs 15 years ago) that other peripherals serially along the 12V rail couldn't receive 12V within a certain error of margin.

here a pic what multiple +12V Rails are:

 

 

 

Yes, its those three big resistory thingys, not connected solderjoints after those things and of course a wire from the Solderjoint to the protection IC.

That's it.

 

What he is talking about is something like a Dual PSU that were around in the mid 2000s that generated multiple +12V Rails like CWT PUC, Enermax Galaxy and some Topower shit as well.

 

But I haven't seen such things around in many years. Maybe, eventually the CWT PUO, but I'm not sure and tend to say its not multiple +12V Voltages generated.

[PineyCreek]

16 hours ago, Stefan Payne said:

here a pic what multiple +12V Rails are:

 

 

 

Yes, its those three big resistory thingys, not connected solderjoints after those things and of course a wire from the Solderjoint to the protection IC.

That's it.

 

What he is talking about is something like a Dual PSU that were around in the mid 2000s that generated multiple +12V Rails like CWT PUC, Enermax Galaxy and some Topower shit as well.

 

But I haven't seen such things around in many years. Maybe, eventually the CWT PUO, but I'm not sure and tend to say its not multiple +12V Voltages generated.

Ah, I figured something would have fundamentally shifted in the 15 years since he gave me that information.  Thank you.  At least now I know what to look for in the future.