I was looking around to see how to determine how much power consumption my rig would be. Well, there is never a definitive answer. Yet you can estimate from specification to get roughly guide.

  1. Mainboard: 50W
  2. CPU: 50-100W
  3. RAM: 5W each stick
  4. HDD: 10W each

That’s for regular parts. For GPU, there are several things to consider from PCI-e specification:

  • Base power - one PCI-e slot has to be provide 75W.
  • 6 Pin PCI Express power connector - maximum power delivery = 75W
  • 8 Pin PCI Express power connector - maximum power delivery = 150W

From this information, you can tell that

  • Gigabyte Radeon R9-280x, which has two power connectors: 6-pin and 8-pin connectors, can draw 75W (PCI-e slot) + 150W (8-pin) + 75W (6-pin) = 300W (total)
  • Gigabyte HD 7870, which has 2 6-pin power connectors, can draw power 75W + 2*(75W) = 225W

For a regular mining rig, weak CPU, with 3 GPUs (7870):

  • 50W Mainboard
  • 50W CPU
  • 5W 4GB RAM
  • 3*225W Gigabye 7870

You will end up having 50W+50W+5W+3*225W = 780W; however, you’d better have at least 20% extra power available which helps power supply unit (PSU) not to be in too heavy load at all time. This simply means you should buy at least 780W * 1.2 = 936W. Surely, you can’t find it, but 1000W PSU is close enough =) Questions?

  • Does AX760i (Great PSU) which can provide 760W work with above example (which theoretically draws 780W) ? I’m sure it’s working. What we are calculating is the maximum power consumption your machine can draw. In practice, it’s never hit 100% mark, but why putting that heavy load on PSU? Its lifespan will get shorter no matter how good it is.
  • What if my machine draw more power than PSU can provide? It depends. (1) Good PSU is likely to shut itself down immediately; (2) some PSU tries harder to provide its juice which cause a ripple. Random reboot or shutdown is likely the result. Lastly (3) PSU is exploded. It is not as bad as it sounds though. In fact, capacitors inside PSU will explode. You will hear and smell clearly if it’s gone. Don’t worry. Maybe a bit of smoke, but mostly your components shouldn’t be damaged, but you never know. :)

Reference: Board Design Guidelines for PCI Express™ Architecture, power supply cable at playtool

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