PSU problem, amps maybe?

[russellito]

I'm a noob, building my first computer.

I have this system, and 2 power supplies. The setup works with one and not the other, Why? When the I say it doesn't work, I mean I switch it on, everything spins for 3-5 seconds then it shuts off.
CPU: AMD Phenom II x4 940 3.0ghz
Mobo: Biostar TA790GX XE
Ram: 4 gb (2gbx2) OCZ DDR2 800
HD: Seagate 7200.11 320gb
LG dvd burner
2 case fans, not sure what size, but not big, maybe 4"?


PSU A that works is an Antec earthwatts 430W ATX 12V v2.2
PSU B that doesn't is some no name 500W ATX
PSU B supports more amps on every voltage except 12v; it supports 14amps. PSU A has 12v1 17amps and 12v2 16amps.
So, my question is why would PSU B not run the system?

 

[rolli59]

It is simple! The Antec is a quality unit with enough amps on the +12 volt to run your system, the no name does not have enough amps on the +12 volt to run a modern system.
Modern systems need amps on the +12 volt rail!
A quality 430watts is better than no name 500watt!

 

[russellito]

Then I guess my next question is what is run off of the 12v rail? And how would I calculate just how many amps I will need off of that rail?

 

[rolli59]

CPU, GPU and storage to start with. There are several psu calculators out there here is one http://extreme.outervision.com/psucalculatorlite.jsp
With a decent to good single dedicated GPU on a modern system the total amps on the +12 volt rail needs to be between 25 and 35 amps today based on the GPU.

 

[cjl]

Basically everything runs off the 12V. CPU, hard drives, and graphics are the main ones. 14A on the 12V is complete garbage for any modern system.


What video card do you have?

 

[JohnnyLucky]

From your description it appears as if the the no name psu has a single +12 volt rail rated at 14 amps while the Antec Earthwatts 430 has two +12 volt rails rated at 17 amps and 16 amps. I know the Earthwatts 500 has two 12 volt rails rated at 17 amps each.

I'b betting you also have a video card that requires decent amount of wattage and amperage.

 

[russellito]

No, there is no video card..yet. There is onboard Radeon HD 3300 128mb.

 

[cjl]

I'm somewhat surprised that the no name doesn't work then. However, definitely keep using the Antec for now - it is the far better PSU of the two.

 

[russellito]

problem is, its my friends psu... So i'll need one that I can keep. any suggestions?

 

[cjl]

Corsair CX400 would be a good choice. If you want to put in a good video card at some point, you might want to go with something a bit better, perhaps a Corsair 550. As a general rule, Corsair, PC Power and Cooling, and Seasonic are among the best choices. Antec is often quite good as well.

 

[AKM880]

I get 16A on my 270W PSU lol. Corsair CX400, or Antec 430W PSU are a good choice.