I have a small box with a Celeron E1400, built-in graphics, one sata hdd, and no optical drives. According to my KillAWatt it uses about 70W idling (CPU @ 34 degrees C) and about 90W under full load (CPU @ 50 degrees C). It's a great little box but the PSU is kind of loud, and given the extremely low power requirements I'd like to replace it with a fanless one. A 200W PSU seems like it would be the most I would need, but unfortunately I can't seem to find anything even near that low that is also fanless.
This box spends most of its time at or near idle, so I'd really prefer not to get some 400+W PSU that's going to be running at really low efficiency just putting out a measly 70W, not to mention the cost.
In short, low power (~ 200W) and fanless: anyone know of anything that fits this bill?
Ok first we need to clarify something:
A power supply will only provide the amount of power the computer needs. If you have a 1000W power supply and the computer needs 50W, the 1000W power supply will only provide 50W. At 80% efficiency, it would draw 62.5W from the wall.
The rated efficiency is the only thing related to efficiency. Most power supplies are 80% + efficient. If you want to spend money on a high efficiency, I think you can get 90% or 87% or something. Efficiency is the amount of power needed to be draw from the wall vs the power is can provide at that amount of power drawn from the wall. Don't assume it will be low efficiency just because it has a higher wattage. Although you are right, most power supplies are most efficient at about 40-70% of their full load.
Consider this also: If your PSU is replaced with a silent or near silent PSU, you are now looking at a more pronounced CPU fan sound. I see no point in going with the fanless PSU unless you also intend to get a passive cooling heatsink for the CPU.
Seasonic is also a good brand. Their PSUs reduce sound by turning off their fan when not needed.
Thanks for the links enzo, you're right they are expensive.
I think I may need to clarify something, however. Obviously the PSU will only provide the amount of power the computer needs, but efficiency is not a static number as you imply, efficiency is a curve that changes depending on load. Rated efficiency certifications only apply at a certain loads. 80 PLUS for instance certifies 80% or better efficiency at 20%, 50%, and 100% load. A 1000W PSU running at 50W is only 5% load, and most PSUs are hugely inefficient in that area.
<a href="http://www.anandtech.com/show/2624/3" target="_blank">This article</a> shows the efficiency for 900W 80 PLUS PSU (it looks like it might even be 80 PLUS Bronze looking at the graph), but notice that below 20% it is falling very fast. The line doesn't even go to 50W, but judging from the slope of the line it might be low 60s or even lower, putting the wall load around 85W. So for a load of 50W I'd be wasting ~35W, which is actually the same amount of power wasted as if the load were 5x higher at 250W. This is why I want to keep the PSU from being overpowered unless I really need to.
And yes, good point on the CPU fan, I was considering going with a fanless option for that as well but I'm not sure. I figured I'd replace the PSU and then see how much it was bugging me.