Power supply question

[Brocman]

For a pc that I am building I have most of the hardware now, I just need to figure out what kind of power supply that I am gonna get and how much voltage I am gonna need. The specs so far are

Intel Core 2 duo E8500 3.16 GHz
GeForce 8800 GTS 512 MB (2 of them SLI)
ASRock P45TURBOTWINS2000 LGA 775 Intel P45 ATX Intel Motherboard

also im gonna put a random tv card into the pc as well.

I was thinking I would need a 650W power supply. But I would like to have one that is a bit above what I need so that it has some head room.

What do you think?

[RaTix]

650w should be more then enough. 450-500w would even be enough for that setup. Well depending on what extra stuff you have attached or installed, like DVD burners, USB devices, extra fans, etc..

This might help you calculate the amps being used to find the wattage needed.

+12V Rail

The most important voltage rail in a power supply is the +12V rail. This voltage rail supplies power to the most demanding components including the processor, drives, cooling fans and graphics cards. All of these items draw a lot of current and as a result you want to make sure that you purchase a unit that supplies enough power to the +12V rail.

With the increasing demands on the 12V lines, many new power supplies have multiple 12V rails that will be listed as +12V1, +12V2 and +12V3 depending on if it has two or three rails. When calculating the amps for the +12V line, it is necessary to look at the total amps produces from all of the 12V rails. Often times there might be a footnote that the combine maximum wattage will be less than the total rating of the rails. Just reverse the above formula to get the maximum combined amps.

* Amperage = Wattage / Voltage

With this information about the +12V rails, one can use it against a general power usage based on the system of the system. Here are the recommendations for the minimum combined 12V rail amperages for various size computer systems:

* Small Form Factor - 15A
* Mini-Tower - 20A
* Mid-Tower - 24A
* Full Tower - 30A
* Dual Video Card (SLI) - 36A

Remember that these are only a recommendation. If you have specific power hungry components, check the power supply requirements with the manufacturer. An example of this might be with the new GeForce 8800 series graphics cards. These cards can easily draw over 200W of power. Running two of the cards in an SLI configuration can easily require a power supply that can sustain at least 750W of total power output.

[Brocman]

Awesome, thanks ratix. I am gonna also have a dvd rom drive, cd burner, plus a couple of fans because the two cards are gonna be close together with one potentially blowing hot air on the other.

I took a look at EVGA's website and they said that this card in SLI mode needs a minnimum of 450 watts.

so maybe im might want to step it up to 750. I can't imagine the system needing anymore then that.

[RaTix]

Do you have two 8800s that your gonna SLI together? If not then the SLI specs don't apply. If your planning on it in the future, then the higher 750w isn't a bad idea.

[Brocman]

yeah it's gonna be two 8800 GTS 512 MB cards