Quad Rail Power Supply

[romeo55]

I just received an Etasis ET850w PSU (850watts, SLI cert. for 8800s)

 

question, Ratings are like this

 

 

Quad 12v Rails, each rated for 18amps right?

 

So why does it sum up to 70 amps instead of 72? and why don't they rate it in watts like the +5v and 3.3v rails???? I'm thinking that that all four can't run at the same time?

 

If the math is done correctly... It should equal 70x12=840 watts??? And yet it is rated for 850watts? or does total power mean "sustained" or "maximum"

 

Last question, Quad rails, For instance, on this PSU, the rails are divided "equally" IE: 12v1 on MOBO/p4 connectors 12v2 on Molexs etc.

 

So what will happen if you go over that 18amp current for one rail? Am i done for? IE: just about ALL of my stuff is hooked up to my molex's IE: Vid card, tons of HDDs etc.... while the 4th rail is sitting there doing nothing (for PCi-e connectors) So will it take extra power from the other rails? or if i go over that one rail... i'm done?

 

Thanks

 

Lilkev... I want you back

Edited December 6, 2006 by The Unforgivin

[Nemo]

From Motherboards.org: Power Supplies 101: A comprehensive guide

A funny thing about dual 12V rails that you need to be aware of is that the capability of the two

+12V rails combined is rarely the same as the sum of the two +12V rails individual capabilities. Using our "Table 1" example, you can see we have a +12V rail that can do 16A and a +12V rail that can do 18A. 16A + 18A is 34A, but the combined wattage for both of the 12V rails is 384W, which is 32A.

 

All that really means is you can't max out both rails at the same time. One or the other is fine, but never both

[romeo55]

From Motherboards.org: Power Supplies 101: A comprehensive guide

 

 

The tutorial goes on to mention quad rail power supplies, but the above example for dual rails gives you an idea. There was a good post here a while back about problems some of the better power supplies had early on powering two video cards in SLI mode and the answer was to try to achieve more even loading across the rails. (I believe - I'm sure someone will correct me if I'm wrong )

 

Basically, with your PSU, each rail is capable of individually providing 12A maximum, but combined they are capable of providing only 70A.

 

Thanks for the pointer!

 

heh, makes me wonder why quad rails were even introduced... trying to spread load accross four rails w/o going over there rating... sheesh...

Edited December 7, 2006 by The Unforgivin

[gotdamojo06]

quad rails just sounds cool...lol

[jammin]

It's worth noting that most "quad-rail" PSUs don't actually physically separate the rails at the PCB level.

 

So basically they are likely to be 'virtual' rails which are actually all connected to the same 12v rail inside the PSU. (Probably something to do with being able to say their PSU meets ATX12V 2.x and EPS12V specs).

[romeo55]

It's worth noting that most "quad-rail" PSUs don't actually physically separate the rails at the PCB level.

 

So basically they are likely to be 'virtual' rails which are actually all connected to the same 12v rail inside the PSU. (Probably something to do with being able to say their PSU meets ATX12V 2.x and EPS12V specs).

 

yeah... what i'm worried about is tho that most of the power from my rig comes from the molex's, and guess what... The molex's are on the same rails as the MB/Cpu <_< The 2nd is for the sata and 8pin, the 3rd is for one set of PCI-e connectors... the other 2 are for the second set... So the last three rails are sitting there doing nothing grrr...

 

*sighs