How do I know how many 12 volt rails are on my computer?

[akurzym]

Hello,
how do I know how many 12 volt rails are on my computer?

 

[hunter315]

Does it really matter? Easiest way, take a look at the sticker on your PSU, it will label each +12V output's max current separately.

This doesnt necessarily mean you have that many though, the majority of PSUs have a single 12 volt source and each rail is split off of this source with a current limit set for each branch, there are also ones that claim multiple rails but dont separate them at all and only claim multiple rails because thats what older spec wanted. Basically the number of rails you have is irrelevant, what counts is the total power available on them combined.

 

[akurzym]

Ok, from the looks of it, I have one +12v rail according to the listing on my original PSU. I am looking to upgrade, is it possible to put too much current on the one rail?

 

[hunter315]

You can pull too much current from a rail, but if you have a single rail design then you dont have to worry about tripping individual rails, you do still have to worry about over drawing the PSU as a whole which can damage it. What PSU do you have and what are the other specs in your system?

You say you are looking to upgrade, what are you looking to upgrade to? General rules of thumb, a good 550W unit(~40A on +12V) will power any single GPU, a good 750W unit(~60A on +12V) will power a two GPU setup, these both leave additional power to spare to keep the PSU cool and efficient.

 

[akurzym]

Right now I have a 250watt PSU. I am looking to add a vid card GeForce 7600gs
A minimum 350W system power supply (with 12V current rating of 20A or more)

current PSU is only 250w rated at 13A on the +12v rail

 

[hunter315]

Wow, your current one definitely needs an upgrade. Most of your components run on the 12V rail, and your PSU only has 156W available to things running on the 12V rail.

I would suggest something more powerful than the 7600GS, maybe something like a 9600GT or a 4670 or a 5670, either of them would be significantly more powerful and wouldnt need a strong PSU. A good cheap one is the corsair 400CX, it will easily power a lower power card.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817139008

It may not seem all that cheap but realize that the super cheap PSUs have explosive tenancies and tend to take out other components when they go.

 

[akurzym]

Only problem is that I am limited to PCI or AGP video cards. Am I correct in assuming that the 7600gs AGP would be better than say a 9500gt PCI?

 

[hunter315]

ouch thats an old system then, but you can get AGP 4650s which would still out perform the 7600GS by a large margin.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150433

The easiest way to compare the cards, take a look at the hierarchy chart, the 7600GS is about mid way down the left side.
http://www.tomshardware.com/reviews/best-gaming-graphics-card,2544-7.html

 

[akurzym]

Thanks for the advice, looks like they have a 4670 that will work with my machine. Although they only list power supply requirements as 400watt min, doesn't say anything about the current needed. Thanks again.

 

[akurzym]

Best answer selected by akurzym.