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dual 12v vs single?

X

Xeon22

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Jan 28, 2003
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Hi,

I've been looking for a new PSU, and I was wondering which would be a better purchase. I've seen some PSUs that have say, 18a on each 12v rail, and I've seen PSUs with a rating of 30a+ on a single rail. Which should I be looking to buy here?
 
If you're not going to OC, just get a recommended PSU (browse the forum a bit) from a reputable company. Dual rails won't matter to you unless you're gonna do heavy OCing. IE trying to max out a P4 prescott, you'd like to have a single beefy 12v rail...

(Yes I know that's a blanket statement, but blanket statements rule.)
 
The number of rails is irrelevant as long as the combined max +12V current is sufficient, UNLESS you have Crossfire X1900XTs or SLI 7950GX2.
 
Can somebody explain to me what "rail fusion" is? Mushkin advertises it for its multirail PSUs and says it's done automatically, but what's the difference between that and just having a bigger single rail?
 
Xeon22 said:
Hi,

I've been looking for a new PSU, and I was wondering which would be a better purchase. I've seen some PSUs that have say, 18a on each 12v rail, and I've seen PSUs with a rating of 30a+ on a single rail. Which should I be looking to buy here?
Click to expand...

The number of 12v rails is not irrelevant, and just getting one from a quality manufacturer you can still be in a world of hurt with a PSU mismatched for the application. So it completely depends on the exact application.
 
Spectre said:
The number of 12v rails is not irrelevant, and just getting one from a quality manufacturer you can still be in a world of hurt with a PSU mismatched for the application. So it completely depends on the exact application.
Click to expand...
What do you mean?
 
454Casull said:
What do you mean?
Click to expand...

That the number of 12v rails is not "irrelevant". An ATX12v2.0 or other multirail psu will quite often have crossloading issue on 5v heavy systems, using a multi 12v rail PSU on certain motherboards is going cause all sorts of trouble (such as the Supermicro H8DCE), multirail PSU's that feed both vidoecards off of the same 12v in certain appliations can be an issue, multiple small 12v's even when cumulatively are large can be an issue, etc, etc.

The 12v configuration is not irrelevant.
 
Spectre said:
That the number of 12v rails is not "irrelevant". An ATX12v2.0 or other multirail psu will quite often have crossloading issue on 5v heavy systems, using a multi 12v rail PSU on certain motherboards is going cause all sorts of trouble (such as the Supermicro H8DCE)
Click to expand...
What is it about the multi-rail configuration that causes these problems?
multirail PSU's that feed both vidoecards off of the same 12v in certain appliations can be an issue
Click to expand...
I did mention this. With 2 7900GTs I suppose there could be a problem if you had a shitload of HDs all seeking at the same time - that is, if HDs are powered from the same rail as PCI-e.
multiple small 12v's even when cumulatively are large can be an issue, etc, etc.
Click to expand...
Multiple small 12V rails? I don't understand.
 
454Casull said:
What is it about the multi-rail configuration that causes these problems?
Click to expand...
croostown.gif

http://www.xbitlabs.com/articles/other/display/psu-methodology_13.html

As for the Supermicro it is about needed power distribution. AreEss explains the issue withthat board best:

Nobody makes a stock multi-rail PSU that has the correct load capability or rail configuration for the H8DCE.
That's a simple fact. Deal with it. You need 28A+ on 12V3 to the 24 pin, 17A+ on 12V1 to the 8 pin, and 17A+ on 12V2 to the 4 pin. (You can of course, swap rail numbers, but you shouldn't.) You MUST have both 4 pin and 8 pin connections. You MUST have native 24 pin EPS12V. You MUST have 1.75A 5VSB+ as well. Those are all absolute requirements.
Click to expand...

There are other boards out that have oddities as well.

Multiple small 12V rails? I don't understand.
Click to expand...

A couple of 8 amp rails will get you in a world of hurt if you just looked at combined rating.
 
So is it just that the PSUs with multiple rails are geared toward PCs with high +12V load and low +5V load?

A couple of 8 amp rails will get you in a world of hurt if you just looked at combined rating.
Click to expand...
Right. I don't know if I've seen any that have less than 10A per rail, if that. Thanks for explaining everything, though.
 
it means that, because older atx standards drew CPU from 5v, new stuff uses 12v

But how geared would an xclio 450bl be for a P5LD2/P-D 930/X1800GTO setup?
 
omega-x said:
it means that, because older atx standards drew CPU from 5v, new stuff uses 12v
Click to expand...
I'm not sure what question you're answering here...
But how geared would an xclio 450bl be for a P5LD2/P-D 930/X1800GTO setup?
Click to expand...
It should provide sufficient power, if that's what you're asking. Too bad their site doesn't list the combined max current for +12V.
 
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