Power budget (cont’d)

With those guidelines in place, you can determine your specific power consumption. Let’s take a typical mid-range gaming Palomino Athlon XP 2000+ system:

Athlon XP 2000+ system
Four fans
- power supply fan
- CPU fan
- Front cooling fan
- Rear exhaust fan
512MB DDR RAM
AGP Graphics card
PCI Sound Card
2 Network cards
2 IDE drives
CD-RW
DVD-ROM
USB printer
Keyboard
Mouse

Sum everything up and that’s
7.3 amps on the +3.3V rail
16.3 amps on the +5V rail
14.5 amps on the +12V rail

Discussion

We know Power = Current * Voltage, and so by the math our minimum power spec is 279W. So all 300W power supplies should be good enough right? And if we wanted to account for “overzealous advertising” we’d be “for sure” safe with a 350W power supply right? Not to mention, those numbers assume that every single drive in your system is being used at the same time, and we’ve already said that the individual components err on the high-end side…

Well not exactly.

At FiringSquad, we don’t think you should expect to sacrifice stability when your system is under full load and so for the rest of this article, we’ll continue to assume 100% power consumption on all devices. That said, because it is rare to have every component active, a reasonable approximation is to assume 80% of your components are active at any given instant and that your CPU is always drawing full power.

Manufacturers can bend the truth when it comes to power supply ratings and you never want to be so close to maximum capacity all the time. At FiringSquad we like for power consumption to be at 80% of advertised maximum and so we need to alter our numbers to account for that. Before I go on, let me say that this is personal preference. We are willing to pay the extra cash for the extra peace of mind, but you don’t need to do this step. But for now, our power demands are:

9.125 amps on the +3.3V rail
20.375 amps on the +5V rail
18.125 amps on the +12V rail
349 W total

So a 350W would be just fine right? We’ve added a fudge factor for misadvertised products right? No, you need to look at the individual rails, remember?