PSU Inquiry

[Cinna696]

Always being skepitical of manufaturers pushing more on the consumer, the tend for higher wattage PSU's annoys me as measuring any of my PSU's (or referencing power draw from relavent reviews on sites such as AT) the power always falls short of 300W.

The dual 12v rail PSU's, 12v1 refers to the origional 4pin molex powering the cpu? and 12v2 refers to the additional 4pins found on the 24pin molex connecting the motherboard (that power the PCI-express lanes)

The power the CPU draws, does all of it come from the 12v1(if this is where its power comes from) rail or is some suplemented elsewhere? How much power does an average A64 consume?

The PCI-Express lane provides up to 150w of power to the GPU, assuming 12v2 provides the power for this 14amps(14ax12v = 162w)on the 12v2 rail be sufficient, or as most PCI-E cards require the 6 pin molex connector, a) what kind of wattage do they draw in addition to the already provides 150w from the 12v2 rail, and b) which rail does it draw this power off of, 12v1. 12v2, 3v, 5v

In addition, what are other common devices found inside the computer that run off the 3v and 5v rail (hd kb mouse cd rom etc...), and does anything else but the CPU and GPU run off the 12v rails and if so which 12v rail do they use. Also what kind of power do common additional items draw.

Now im not looking for psu recommendations or to be told which are the best, the questions are specific and are to help me (or anyone) referencing overall power implementation in any future system

Thanks in advance for any help on any of this, i did try searching online and within the forums however came up quite short in regards to specifics and such. Basically i believe what im looking to learn here is how to choose the ideal PSU for any system by looking at its power ratings knowing what i can expect devices to draw and provide adequate power with just enough overhead.

Forgive me if i this sounds like something Dell does so they don't have to spend more $ than absolutly neccesary, i just honestly believe ****** has gotten out of control with regards to 500 and 600 watt PSU's that are unnecesary.

 

[Bassyhead]

This topic should probably be in General Hardware but here goes:

The individual current ratings you see for each voltage on a power supply's label is the maximum rating for each voltage, they aren't supposed to add up equal to the maximum rating for the entire supply as the supply cannot deliver the maximum load for all voltages simultaneously. Typically if you do the math the rating from adding up all the maximum power exceeds the power rating of the power supply.

The 3.3V/5V supplies are regulated together and each 12V supply is individually regulated. The ATX12V specification calls for a secondary 12V supply to be available when greater than 18A of 12V is required on the primary supply. On today's motherboards, voltage regulation designs for CPUs draw power from the 12V supply. As you mentioned, PCI-E can draw up to 150W so this necessitates the need for an auxiliary 12V supply. The 12V supplies are also used for most drive motors (especially if you have a high speed hard drive). I think the 5V and 3.3V supplies are still extensively used for PCI cards, RAM and maybe AGP.

Dell and other OEMS typically use the lowest powered supplies as possible. Usually the computers they sell are not as power demanding as enthusiasts such as on these forums require, so they can get away with it. Additionally, in my experience, these power supplies are much better in quality than some of the cheap supplies that are often bundled with cases.

500 to 600 watt supplies are not out of the question. If you do the math, the maximum you could deliver 12V with the current ATX12V specification is 432 watts. Consumer grade power supplies don't do too well when pushed to their peaks, so don't skimp on the PSU if you're investing in a top-of-the-line computer. The specification allows a lot of headroom for future expansion. Updating specifications and hardware is costly and avoided.

 

[MrDudeMan]

500-600 watts is too much for normal, middle of the line computers. i have a dual core, 7800GT, and 2 10krpm hard drives as well as 4 120mm fans and some other random junk. i did a PSU calculator (found in GH with a search) and it said i needed 400 or 420 or something close to that. i picked a 550 watt PSU to have some headroom, but also because it is modular and i can unplug the cables i dont need.

[rant]

on a side note, it really annoys me when people who know nothing about electricity complain about modular PSUs. they say the connection adds resistance equivalent to 2 feet of wire. well whoop-de-do! 2 feet of copper wire is completely negligible when the resistance in the hardware will be orders of magnitude more than the total resistance between the voltage supply and the load. i actually took the time to do the calculations about 2 months ago and the modular connectors drop on the order of millivolts...like that is going to affect anything :roll:

[/rant]

 

[GalvanizedYankee]

OP, I did offer you two links over in GH. Form Factors.org offers the parade of spec that has occured over the years. The PureOC link offered a very good explaination as to why the cheaper high wattage PSUs output falls as they heat up. A cheap 500 watt unit might drop to 350 watts at 35C.
Note too that the -5V line is being speced out.

This link is somewhat dated as it doesn't list the most current hardware but it does give a detailed breakdown of what line serves what.

http://takaman.jp/D/?english jonnyGURU a member of this board and a reviewer of PSUs reccomended this calculator at one time.


Modular?? In and of itself is not bad but the rush to market, cheaply executed is.


...Galvanized