PSU Questions In-Depth for experts

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Aussie_Dundee

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Joined
Oct 17, 2007
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110
Hello

My comp specs:
Mobo - Asus P5N32-e SLI Plus
CPU - Intel E6550
GFX - Asus GN7600GS silent 256mb
HDD - Western Digital Raptor 74gb 10,000 rpm
HDD2 - Old piece of crap IDE drive at around 80gb for backup.
DVD - Generic crap
Ram - 2x1gb Corsair xms2 heatsink CL4 800mhz
Chassi - Antec P182

No extra fans och cooling yet,
Nothing Overclocked either


I'm trying to figure out the amp requirements of the mobo i have bought. While doing this i realised a few holes in my understanding of the psu.
When talking about diffrent rails a psu has. are we comparing this to parallel and serial voltage flow?
As in.. the cpu needs 13 amp max for 10ms meaning i need a 12v rail with at least 13 amps ouput steady at 50celsius.

1)But does the mobo isolate the cpu's power supply from other hardware so that no matter what the strain is on the other rails the rail for the cpu is allways dedicated?

2) Talking about a 2 rail psu, does this mean the other rail supplies the mobo and all its components with the other rails power output? as in pci cards. sound. graphics, usb etc.

3) What rail in that case powers the hard drives the fans connected directly to the psu and not through the mobo and the disk units DVD etc...?

4) given that a sli setup uses 2 gfx that both need external power wouldnt this make a total of 5 rails?
1xgfx1 2xgfx2 3xmobo 4xcpu 5xfans drives etc.

5) how does a multi rail psu differ from a single rail psu with a higher amp single rail?

6) am i correct in assuming that the 12v2 is the powering the cpu? and in this case is t possible to run a 12v1 rail of lets say 18 amp while the other rail is 13 amps since thats all i need? if there was such a PSU.

7) cant find the amp requirements of my any of my hardware except the cpu and raptor hdd. 13 amp for cpu and 10 watts or 0.5 amps roughly respectively... anyone know them or know where to look? i allready tried www.asus.com etc... doesnt say.

Thanks in advance for any help
 

Aussie_Dundee

Thread Starter
Joined
Oct 17, 2007
Messages
110
It works fine. except most of the choices are very outdated. IT still lets you choose pentium II for example. but duo or quad cores arent listed yet. Same goes for graphics cards :(

Thnx anyway
 
Joined
Jul 19, 2005
Messages
11,670
I am certainly not an expert, but I will attempt to answer the questions.

QUOTE=Aussie_Dundee
As in.. the cpu needs 13 amp max for 10ms meaning i need a 12v rail with at least 13 amps ouput steady at 50celsius.

Your Intel E-6550 has an Intel PCG of 06. An 06 platform has an Intel recommended amperage requirement on the +12V2 rail 8A continuous and 13A peak for at least 10ms, NOT 13A continuous.

QUOTE=Aussie_Dundee 1)But does the mobo isolate the cpu's power supply from other hardware so that no matter what the strain is on the other rails the rail for the cpu is allways dedicated?

The power supply according to ATX specs should be wired so the +12v2 rail is isolated. This specification is sometimes not followed as discussed here; http://www.xbitlabs.com/articles/other/display/psu-roundup_2.html

QUOTE=Aussie_Dundee 2) Talking about a 2 rail psu, does this mean the other rail supplies the mobo and all its components with the other rails power output? as in pci cards. sound. graphics, usb etc.

It SHOULD as +12v2 should be isolated, but as described in the previous posted link, sometimes this spec is not followed. With higher powered processors this could cause problems as discussed in the previous link.

QUOTE=Aussie_Dundee 3) What rail in that case powers the hard drives the fans connected directly to the psu and not through the mobo and the disk units DVD etc...?

All the power for the other components in the case SHOULD be provided by +12v1, +12v3, or +12v4

QUOTE=Aussie_Dundee 4) given that a sli setup uses 2 gfx that both need external power wouldnt this make a total of 5 rails? 1xgfx1 2xgfx2 3xmobo 4xcpu 5xfans drives etc.

No, with SLI the voltage/amperage required by the video cards should be supplied by +12v1, +12v3, and +12v4. The amperage is raised on these rails to supply the proper power for the cards. To the best of my knowledge there is no power supply with a +12v5 rail.

QUOTE=Aussie_Dundee 5) how does a multi rail psu differ from a single rail psu with a higher amp single rail?

A single rail power supply supply's all the +12 power from a single rail, whereas a multi rail PSU splits the +12v power on 1, 2 3 or 4 rails. Some power supply's may provide for power sharing between rails such as this one; http://www.corsairmicro.com/products/hx.aspx
Read the attributes for this PSU in the left hand column and you will see this statement;

"Triple 12V Rails provide independent reliable power to the CPU, video card and other components with a combined rating of 50A (40A on 520W) maximum! Advanced circuitry design that automatically enables power sharing between the triple +12V rails in an event of overload on any single +12V rail".

This is why I prefer a PSU with a large single +12v rail. In a PSU with a large +12v rail I don't have to worry about power being lost on another +12v rail or whether the PSU has provisions for power sharing between rails.

QUOTE=Aussie_Dundee 6) am i correct in assuming that the 12v2 is the powering the cpu? and in this case is t possible to run a 12v1 rail of lets say 18 amp while the other rail is 13 amps since thats all i need? if there was such a PSU.

Yes, this power supply advertises the attributes such as you describe with 4 +12v rails with different amperages per rail. http://www.newegg.com/Product/Product.aspx?Item=N82E16817163108

According to ATX specs, if the +12v2 rail has greater power than the other rails, instead of 2 yellow and 2 black wires for the +12v2 processor auxiliary power, the power supply will have for the +12v2 auxiliary rail 2 yellow wires with black stripes and 2 black wires.

QUOTE=Aussie_Dundee 7) cant find the amp requirements of my any of my hardware except the cpu and raptor hdd. 13 amp for cpu and 10 watts or 0.5 amps roughly respectively... anyone know them or know where to look? i allready tried www.asus.com etc... doesnt say.

Try the caulculator here; http://www.extreme.outervision.com/ For an extra $5 or $6 USD you can subscribe to the Pro Version that gives you a better breakdown. I have never seen an online calculator that I considered 100% accurate. I always figure for more power than the calculators indicate.
 
Joined
Jul 19, 2005
Messages
11,670
I gave you some misinformation in the answer to a question I want to correct.

I said; "To the best of my knowledge there is no power supply with a +12v5 rail." I was looking around a little today, and I see now that Coolermaster has a PSU with 6 +12v rails, and Enermax has a PSU out with 5 +12v rails. I stand corrected. There may be more, I just didn't spend a lot of time looking.

Lol, if this keeps up pretty soon someone will need to fabricate a "super" chassis just to support the PSU.
 

Aussie_Dundee

Thread Starter
Joined
Oct 17, 2007
Messages
110
(y) :D
Cement block base with a new form factor standard double the size of the older smaller ATX
Found PSU's the size of chassis while i was researching he subject so... its not impossible ^^
 
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