Phil wrote:
How do I know if im running off the one rail as opposed to the other?

On Apr 16, 4:24 am, "DRS" wrote:
"Phil" wrote in message

oups.com

I am about to buy a geforce 8800GTS 320MB card. It says minimum
requirements for the card is 400W and 12V rated at 26A. My power
supply is 400 watts but only rated for 12V at 18A. You think I could
pull that off or should I buy a new PSU?
It depends. If your PSU only has a single 18A rail then you'll probably not
get away with it (the 8800GTS will draw peak about 11A, the CPU around 10A,
a HD 1A, etc). If you have at least 2 12v rails of 18A nominal capacity you
should be ok if you run the card off one and the system off the other.



On dual rail PSU's, 12V1 is for the CPU/MOBO only, the rest of the
system goes off the 12V2. But I think most modern PSU's have only
"virtual" rails and it's effectively just a way to get around the 20A
max per rail required by a 240V system.

I'm running a 500W w/ 2 x 18A rails and it runs my 8800GTS fine. I've
also got 3 HD's, 2 DVD/RW's, and 2 other PCI cards on an A64 system.
36A more than meets the 29A spec, but I wouldn't chance it with a 400w @
26A, since you have to calculate 80% efficiency with headroom (you don't
get max voltage all the time).