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View Full Version : PSU rails and the components that love them


alex666
02-08-2005, 12:37 PM
Greetings PC Guide, it's been a while.

I know that psus have +3.3, +5, and +12 volt rails, plus the -12 and I think it's the -5, or something like that. Plus, some actually have 2 +12 volt rails.

Anyway, my question is as follows: which system/mobo components are run by the 12, the 5, and the 3.3 volt rails, respectively? For example, is system memory run off the +5 volt rail, the hdd off the 3.3, video card off the 12, whatever? I'm asking this in the hope that I can look at my voltages (either in the bios or through something like MB monitor) to see if a particular system component problem (e.g., memory) I'm having might be associated with the voltage output on the particular rail that powers that component.

I've read up on psus quite a bit, but I've never come across an article that matches components to rails, if indeed that's how it works. Anyone know a good reference to this question? I've googled, but no luck. Thanks.

marty

alex666
02-10-2005, 12:18 PM
Bump. Anybody??

Mick_D
02-10-2005, 03:59 PM
Here is one link that may help. http://www.pcpowerandcooling.com/maxpc/index_cases.htm

Whyzman
02-10-2005, 05:43 PM
Interesting in the footnotes the link states that today's systems draw disproportionally on the 12+ rail...yet, many of the PSUs are still being manufactured based on the old system requirements...

Important to check out the rail amp allocations based on your systems components...especially when running beaucoup fans!

Here's a good article: http://www.firingsquad.com/guides/power_supply/

alex666
02-10-2005, 06:12 PM
Thanks all. Yeah, it seems like power supplies are finally getting the recognition they need when planning a system, especially with the chips and video cards demanding more and more juice. It's interesting to see what components draw from where.

marty

Fruss Tray Ted
02-10-2005, 06:23 PM
Whyzman,
No disrespect to you but I want to comment on the other link prior to checking your's out.

The first one lists,
The power requirements of the individual components is not separated when one peripheral uses a source of two voltages. This makes it a problem with deciding on a PSU and even when diagnosing in the field. The article mentions total consumption but not on which rail. Sooo, we dig further...

But, IMO, 'generaily' speaking, 'motors' etal, fans, harddrives, optical drives, excepting floppy drives, use the 12 volt rail to drives their motors. When you 'starterr' lacking power in that sense, go grab your car battery and "hooker'up". Bigger is better! The power supplies that come with externals have low power 5v rail but better 12v as that's the greater current draw.

Does this post make me look disproportional? :confused: :eek: :D

Whyzman
02-10-2005, 08:09 PM
Not at all...I'm a "Tim the Toolman" kinda guy! More Power to ya! :)