I've been building systems for myself for awhile now, but I am and always have been a little confused about the 12v rail topic. I've ordered a new video card and I wonder if my PSU has enough amps for it.
The power supply that I have is a Seasonic S12 600w. The video card I purchased is the EVGA Geforce GTX 470 which requires "38 Amps on a +12V rail." I've looked up the specs for my PSU and besides having the required 2 6 pin PCI-E connectors, its specs say that it has two 18A 12V rails that power the PCI-E plugs.
I'm clueless about how all of this stuff adds up. I've read that they the amps don't simply add up, and even if they did it wouldn't add up to 38. Will I be ok or should I be looking at a new PSU as well? Thanks for any help.
4GB (2 sticks) RAM
4 sata HDs
4 case fans
IDE DVD drive
It should be just enough, the Seasonic is a pretty high quality PSU Id trust. The Seasonic is rated to do 432W on the 12V rail, which is enough for a single GTX470+i7, as long both are at stock. Wont trust an OC for it though.
The 38A is an pretty optimistic number for people with an not so good PSU. A system with a single GTX470 shouldn't use 38A(456W), maybe 350-370W.
I'm clueless about how all of this stuff adds up. I've read that they the amps don't simply add up, and even if they did it wouldn't add up to 38.
Yes you will be fine.
As for how it adds up, in my experience it varies with models and brands. You will need to find out the total wattage that the total of all +12V rails can supply, usually in manufacturer specs. Remember that P=VI (power in watts equals volts times amperage) so basically, since the voltage is a constant 12V, you can say that the GTX470 calls for a 12V rail capable of 456A, which makes sense since they are also trying to take into account anything else you might have in the system drawing from those rails. They want to be safe but if you look up the specs of the GTX470, it only requires 215W maximum by itself (yes I know it is TDP not the maximum power draw but it is a close enough estimate).
According to this, your PSU has the capability of outputting 432W on the +12V rails in total: A long link
What else draws from your +12V rails?
-The i7 has a TDP of 130W
-HDD draw no more than 10W each but not all from the +12V rails
-I'm not sure about the case fans and DVD drive but they don't draw much power anyway
Hmm... I may have tried to hard. Main point though: You have enough power, just don't add a second card for SLI in the future.