Can i use more than one rail to power GPU? How?

[d359233drdrbcom]

psu has four 18A rails and only one pci-e connector.

1If i use cable adapter to pci-e what rail/s will i be using then?
2How many ampers should i expect from adapter?
3What adapter is best?

 

[Someone Somewhere]

Depends on the PSU. What PSU and what GPU?

 

[Ra_V_en]

Not sure what do you mean by rail.

1) and 2) How do we know that if you didn't put any info about the PSU.
3) The one with golden pins.... are you serious with that question?

 

[YasminFreitas]

And, as you can see, regardless of which graphics card you use, there is more than one way for power to be distributed to it: 75W at 6.25A, just from the PCI-E ...


http://www.mobitvfree.blogspot.com/2012/09/spike-tv-live-streaming.html

 

[Someone Somewhere]

Huh? Gold pins can be a waste of money in certain cases. If it's staying plugged for a long time out of any moisture, tin plated is fine. Plus there's all sorts of different wiring options.

A rail is a separate set of overcurrent protection on the PSU, because a partial short might not hit the ~60A needed to cut of a medium-large PSU, while still doing serious damage.

 

[d359233drdrbcom]

Depends on the PSU. What PSU and what GPU?

I dont know what psu yet.Im asking questions because I dont know which PSU to get.
I ll prolly get at least radeon 7950


So how can i find out 1) and 2) just by looking at psu specs?

 

[Someone Somewhere]

So you haven't decided on a PSU? How do you know it's only got one PCI-E connector?

Any PSU with only one PCI-E connector probably isn't enough for a 7950.

Don't cheap out on a PSU.

 

[d359233drdrbcom]

So you haven't decided on a PSU? How do you know it's only got one PCI-E connector?

Any PSU with only one PCI-E connector probably isn't enough for a 7950.

Don't cheap out on a PSU.

im supposing ill buy this psu but dont count on it. ms-tech system builder 640W

i still have many other psu to check so i need to be able to find out if the psu im checking is good or nor for my build.

 

[Someone Somewhere]

Run a mile. Passive PFC, no efficiency ratings, no-name brand.

Look for something 550W+ from the second link in my sig.

 

[d359233drdrbcom]

Run a mile. Passive PFC, no efficiency ratings, no-name brand.

Look for something 550W+ from the second link in my sig.

ok but if i go there i still wont be able to know how to becasue my questions havent been solved.

So how do I check what rails can i use in a psu to power gpu?Can i sue more rails if i use a adapter like molex to pci-e?

 

[Someone Somewhere]

Rails aren't an issue on any well designed PSU. If it has enough PCIe cables, it will be wired such that the cables are split between rails enough not to overload any individual rail.

You can, but you might overload the peripheral rail. Not a good idea.

 

[unksol]

do not buy that PSU. you should get a well reviewed quality brand PSU with a SINGLE 12V rail. multiple rail designs are from an old outdated spec and they aren't actually separate rails anyway.

most manufactures using them do it to trick people. no real 640W PSU would only have 1 pcie connector. and if it were REALLY 4 12V rails at 18A it would be 870W+. they are clearly lying which means run away.

 

[d359233drdrbcom]

do not buy that PSU. you should get a well reviewed quality brand PSU with a SINGLE 12V rail. multiple rail designs are from an old outdated spec and they aren't actually separate rails anyway.

most manufactures using them do it to trick people. no real 640W PSU would only have 1 pcie connector. and if it were REALLY 4 12V rails at 18A it would be 870W+. they are clearly lying which means run away.

If there is some protection like OverPowerProtection OPP on each rail then it would react quicker than one rail with much bigger Amperage

(this psu has different rails and the 4 18A rails psu is Ms tech 750W i think but it isnt important anymore)

Maybe each rail really has 18A but you cant use all of them at max A because the psu lacks Watts?

 

[Someone Somewhere]

Each rail has a current sensor that trips the PSU at a little over 18A. The PSU itself is rated for 640W, a certain amount of which can be delivered at 12V (though I'm skeptical as to whether it can do rated wattage). The total 12V output would be somewhere in the range of 45A.

 

[d359233drdrbcom]

So how do i know if psu which hasnt enough Ampers on single rail to power a gpu can power the gpu using more than one rail?

 

[Someone Somewhere]

That's what connector ratings are for. If they stick two 8pin (150W) connectors, they'll either be on different rails or on a rail with more than 25A rating.

The people who design these do it so that you don't have to worry.

 

[d359233drdrbcom]

That's what connector ratings are for. If they stick two 8pin (150W) connectors, they'll either be on different rails or on a rail with more than 25A rating.

The people who design these do it so that you don't have to worry.

ok thats good to know but what if psu has only one pci-e connector?

Why 25A? . (25A * 12V = 300W atts)

 

[Someone Somewhere]

Note that I said two 150W connectors. 2x150=300.

Any PSU with less than two PCIe connectors probably isn't powerful enough, and should be avoided. Seriously.

 

[d359233drdrbcom]

Note that I said two 150W connectors. 2x150=300.

Any PSU with less than two PCIe connectors probably isn't powerful enough, and should be avoided. Seriously.

well if it has enough ampers and volts then it has enough watts = power.
can you answer my question now?

 

[Someone Somewhere]

Not necessarily, because the power may not all be available at 12V. Plus, many cheap PSUs (few PCIe cables is an indication of this) can't output anywhere near the amount of power on the label.

 

[d359233drdrbcom]

Not necessarily, because the power may not all be available at 12V.

why not?

 

[Someone Somewhere]

Because of 3.3/5V, plus the negatives.

 

[d359233drdrbcom]

what is the difference if it negative?

 

[Someone Somewhere]

Most modern PSUs output four different voltages: +12V, +5V, +3.3V, and -12V. Some also do -5V.

Generally, the total output is the maximum sum of them all. You can't draw the whole PSU's load one one voltage; each has a limit.

 

[d359233drdrbcom]

Most modern PSUs output four different voltages: +12V, +5V, +3.3V, and -12V. Some also do -5V.

Generally, the total output is the maximum sum of them all. You can't draw the whole PSU's load one one voltage; each has a limit.

and that limit is the amper specified for the rail times the voltage for that rail?

is it better to use 5v rail instead of -5v?
or 12v vs -12v