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Some Questions.

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I have some more questions about power supplies.

 

With all the Multiple Railed PSU's out there now what does it all mean.

For Example. Are Four 12V @ 18 Amps Each == 72 Amps? If so what does this mean for Video card requirements that state for example 22 Amps needed on 12V rail. Are More Rails Better or is just one or two Rails with High amperage better then it being spread out?

 

I still don't understand how the Mutiple rails are separated. Are they separated by actual connections or are they virtual. In that does the power supply "sense" where more Amps are needed/drawn?

 

For Singled Railed Power supplies are they more unstable because all the amps are on one rail or are they More Stable then Ones with multiple Rails. Kind of related to my first Question.

 

These are mainly directed at Lilkev. But Anyone can reply.

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These are mainly directed at Lilkev. But Anyone can reply.

 

DUH! :P

 

And i believe the load is distributed accross the seperate rails. I think it has something to do with larger rails having stablity issues... However, i'm really unsure on this... So if anyone knows for sure, please confirm or correct :)

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I'll try to explain this the best that I can.

 

With all the Multiple Railed PSU's out there now what does it all mean.

For Example. Are Four 12V @ 18 Amps Each == 72 Amps?

Here is a PSU review from JonnyGuru for a example that fits this scenario pretty good. There are 4 12v rails with a rating of 18amps, but notice that the combined total output of all of the 12v rails is 680watts/~56.66amps. Each individual 12v rail is capable of 18amps, but the total combined cannot exceed ~56amps due to the fact that the main transformer/output caps has a limit.

 

If so what does this mean for Video card requirements that state for example 22 Amps needed on 12V rail.
That figure is usually given for the total amount of combined amps for the 12v rails. A PCI-Express video card can consume up to around 150watts max: 75watts from the actual 16X connector and another 75watts from the 6-pin PCI-Express power connector.

 

Are More Rails Better or is just one or two Rails with High amperage better then it being spread out?
It depends on the scenario. Lets say in a SLI configuration both PCI-Express power connectors draw power from the same 12v rail... then that particular rail can become overloaded since per the Intel ATX v2.X specs the max amps per 12v rail is 20amps.

 

I still don't understand how the Mutiple rails are separated. Are they separated by actual connections or are they virtual.

The 4/8pin 12v CPU power connector usually has its own dedicated 12v rail. The other rails are for the ATX connector, molex, sata, PCI-express, etc. The manufacturer decides on how to distribute the connectors on which rail. Usually the only way to know which power connectors are on which label is to open up the PSU and take a look where the groups of 12v wires are soldered onto the PCB. They will be labeled 12v1, 12v2, etc.

 

In that does the power supply "sense" where more Amps are needed/drawn?

The output caps can only supply so much power, hence they are given a uF (microfarad) rating. When the power draw exceeds the output rating of the capacitor the PSU cannot supply enough power, usually resulting in a reboot/freeze of the system.

 

For Singled Railed Power supplies are they more unstable because all the amps are on one rail or are they More Stable then Ones with multiple Rails. Kind of related to my first Question.

Again it has to do with the power draw. With a large single 12v rail the manufacturer has to use a higher rated output capacitor (which costs more obviously). The idea behind multiple 12v rails from the ATX spec is purely for safety reasons. By caping the total 12v output per rail to 20 amps (or lower) the risk of a cap exploding, etc. from heavy power draws is reduced.

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Thank You, That was Very HelpFul. :)

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:google: is your best friend :) Here's what I found at Wikipedia:

 

ATX standard

On a modern ATX computer PSU, there are usually three primary voltage rails: one +3.3V, one +5V and as many as four +12V rails. Each of these supplies power to the various components of the computer system.

 

+3.3V: This rail has its own circuitry in the PSU which generates the voltage. It has many wires and power connectors to distribute the 3.3 volts to components which require 3.3V. As microchip technology improved by squeezing a larger number of small transistors onto the chips, the voltage requirements for these transistors drops. The ATX standard added this 3.3V rail to power newer chips.

+5V: Has its own separate set of circuitry, wires, and connectors.

+12V: In modern PSUs, the most important voltage rail is the +12V rail which supplies power to components that draw the most amount of current. These are usually the cpu, hard drives or other storage peripherals, cooling devices, and video cards. Current fluctuations will usually cause malfunction, hence the importance of a good +12V rail. As such, modern ATX12V PSUs may have as many as four separate +12V rails. Like the 3.3V and 5V rails, each 12V rail has its own set of wires and connectors.

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