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Help understanding power supply requirements

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July 31, 2006 4:43:51 PM

I am going to build a new system for the first time. I am trying to pick the correct power supply for this build. I am going to use a Radeon X1900XT 512MB 256-bit GDDR3 video card. The system requirements state that I need:

# 450-Watt power supply or greater, 30 Amps on 12 volt rail recommended (assumes fully loaded system)
# For CrossFire™: 550 watt power supply or greater, 38 Amps on 12 volt rail

What does this mean 30 Amps on 12 volt rail?
Here is a list of the parts for my computer build(from Newegg):

Antec SmartPower 2.0 SP-500 ATX12V 500W Power Supply - Retail

Lian Li PC-V1200Aplus II Silver Aluminum ATX Mid Tower Computer Case - Retail
ASUS P5W DH DELUXE/WIFI-AP Socket T (LGA 775) Intel 975X ATX Intel Motherboard - Retail
ATI 100-435801 Radeon X1900XT 512MB GDDR3 PCI Express x16 Video Card - Retail
Intel Pentium D 950 Presler 800MHz FSB LGA 775 Dual Core Processor Model BX80553950 - Retail
CORSAIR XMS2 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Unbuffered Dual Channel Kit System Memory Model TWIN2X2048-6400 - Retail
Western Digital Caviar SE16 WD2500KS 250GB 7200 RPM SATA 3.0Gb/s Hard Drive - OEM
ViewSonic VX922 Black/Silver 19" 2ms LCD Monitor - Retail
ASUS Silver ATAPI/E-IDE DVD-ROM Drive Model DVD-E616A2 SV - Retail
NEC 16X DVD±R DVD Burner Silver IDE/ATAPI Model ND-3550A - OEM
Microsoft Windows XP Professional With SP2 - OEM
Lian Li C-01A CD/DVD ROM Bezel - Retail

This power supply states that it has +3.3V@32A, +5V@35A, +12V1@17A, +12V2@19A, -12V@0.3A, +5VSB@2A.
Does this mean that it has a total of 36amps on the +12V rail?
And what does it mean by Efficiency 70%(min.) at full and typical loads. Does this mean that you only get 70% of the 36Amps which would be about 25Amps?
Do you think this power supply will work for this build?
I like the idea of modular cabel design..

Thanks
July 31, 2006 5:14:07 PM

In short this power supply should work. You are right it does deliver 36 amps on the 12 volt rail.

Efficiency has to do with power input rather than output. The more efficient the powersupply the less input power it will need to produce the output. This tends to affect electricity bills and how hot the powersupply gets.

I understand that Antec is a good brand but you should here from others with more experience with it whether its specs are accurate or conservative.
July 31, 2006 6:08:42 PM

Personally, I would go for a bit more wattage, but looks great. 36A should be ample for a single-GPU setup...

~Ibrahim~
Related resources
a b ) Power supply
August 1, 2006 1:23:10 AM

Well one thing is that you're trying to install a heatpipe cooled mobo in an inverted mobo case. That's not a great idea but it might work.

Heat pipes are tubes with liquid in them. Gravity pulls it down next to the part that needs cooling. That part boils the liquid and it moves up to the heatsink. This effect doesn't work upside down. Some heat pipes are stinted meaning they have a bunch of wicks in them so gravity is less a factor. However even stinted heat pipes have trouble going directly against gravity.

For info on PSUs try:
http://www.motherboards.org/articles/guides/1487_1.html
August 1, 2006 2:12:10 AM

that should be ok for your setup,but if you dont mind spending a little extra $$ look at this antec http://www.newegg.com/Product/Product.asp?item=N82E1681... it is what i have and its quiet and powers all my stuff ( 2 video cards 3 hard drives and 2 optical drives a floppy/card reader and 2 120 mm fans) it also has the cable system where you only put in as many cables as you need.
!