PicoPSU vs ATX PSU for powering small server with several HDDs.
I've been considering various options for building a small all-purpose server that would run 24/7. I wanted it to be very power efficient while retaining ability to run mainstream linux distros. That in the end meant setting on some cheap Apollo Lake or Gemini Lake 4 core with 4 SATA ports like J4105-ITX.
The issue I have is how to efficiently provide power to board that idles around 10W. There are two options I see:
- PicoPSU around 90W. Main pro is better efficiency, but some shops recommend against using 3.5" HDDs with them. I wanted to put 2-3 WD Reds in the build. I'm also worried about power spike when disks spin up.
- 80 Plus Bronze 300W ATX PSU like this one. It is actually cheaper option (and much easier to source), since I plan on using Fractal Design Core 500 case there is no extra space wasted. It will certainly have zero issues with peak power draw, but I'm worried about how much power will it use when server idles.
Do you have any experiences to share about this? Or some reviews that test ATX PSU efficiency at 10-20W.
Posted Dec 7, 2018, 10:43 AM UTC
1420
Lets assume that the ATX Bronze PSU has a efficiency rating of 75% when running at 30w and below (Worst case and would most likely be up around 80-85% depending on 110v vs 240v). Drawing 20W of power would equate to pulling 27W from the wall to give you the 75% efficiency. You have then wasted 7w of power per hour. This translates to 0.168KW per day of inefficiency. Let's round to 0.17 for calculation sake. I don't know how much power costs in your country but here in australia we usually pay around 25 cents per kilawatt. This would mean I would pay 4.2 cents per day in wasted power.
Pulling Info from this sheet which is the data sheet of a 60w ac-dc adapter, the typical efficiency is listed at >=88%. Plugging 88% into the above calculation gives 2.7W of wasted power which equates to roughly 1.6 cents per day.
Efficiency at such a low load is basically an insignificant consideration when you are comparing cents per day. Hell, worst case scenario as outlined above, 2.6 cent per day difference equates to $18.9 over the course of 2 years. It would work out cheaper so long as the ATX PSU is greater then $18.9 cheaper when examining a 2 year lifespan.
I'm in full agreement with your math. It's just the very first assumption you are making that I'm not sure about. I'm literally worried that 80 Plus Bronze PSU might just as well have sub 50% efficiency at around 20W.
EDIT: I also hope to use it for much longer than 2 years.
Tom's Hardware tests PSU efficiency including at 20w load. This test is for a white label PSU (not as efficient as a Bronze) that hits 68.6% load at 20w. This is also a higher wattage PSU which will also have worse efficiency at low wattage than a 300w. It won't hit 50%. Even if it did, you would be looking at around 5 cents a day difference between a 50%-88%. It really won't be noticeable.