Here's my experience that triggered this 1st blog post... as the story goes in the last month I thought of building a low power home server.
So I got this:
- Case + PSU Asus Pundit AE3 - µATX desktop case + 275W PSU
- Atom bog stock mobo w/ D510 dual core HT enabled CPU
- Seagate Momentus .4 OS drive
- 2GB DDR2 in 1 stick
What about "Power Consumption"? Math warning! It took 41W at the wall socket irrespective of the load and here's why:
- all the components listed above can't possibly consume more than 20W
- the difference to 41W must be PSU inefficiency
- 41W represents 14% PSU rated power; 20W is under 10%
- even a 80+Gold rated PSU (which mine isn't) is horrendous @10% load.
Yesterday 2x 2TB Samsung EG arrived and the server now consumes 45W at the socket. Xbitlabs measured these HDD's load power consumption @6W - and both on my rig added only 4W. What happened is:
- component's consumption probably rised by 12W thus pushing the total consumption to some 32W by my guesstimate
- 32W is ~12% PSU rated power; the PSU is more efficient at this load than at the previous 8%
- efficiency rose from ~50% to 70%
I got my case+PSU for cheap, but in the long run I may have to change the PSU with a lower wattage model. The idea is to land the power consumption in the maximum efficiency range, which is between 20 and 80% of the rated power.
It's maybe hard to grasp that below 20% PSU efficiency can be so low, so I wrote this post to share my thoughts. Here is my guide to buying a PSU:
- compute idle power (iW); I'll peg iW @25% PSU rated power so that efficiency is good @idle usage
- multiply iW by 4 to get the necessary PSU rated wattage (25%*4=100%)
These midrange PCs don't need more than 400W PSUs. Having a lower power PSU is cheaper to purchase and run and it is quieter because losses are low.