Low power computing - was Any suggestions, please?

[David Fletcher]

On Saturday 11 Sep 2010, Basil Chupin wrote:
> On 11/09/2010 02:49, David Fletcher wrote:
> 
> Most interesting, David. Thanks for this post and pic. I'll keep in mind.
My pleasure, Basil. The picture might not be on there for ever so keep a copy 
for reference it you like.

> 
> You are referring to your "server". But what do you use as your "client"?
I'm using the Athlon dual core that I built a couple of years or so ago. I've 
now edited my MX record so that my messages get squirted by the Internet 
directly into this server. Postfix sorts out the messages with an aliases 
table, then I'm now using dovecot-imapd to access my mail using kmail, 
thunderbird, whatever I want from the Athlon. Port 993 is forwarded by the 
router to the server so that I can use it from my laptop when I'm away. 
Pretty standard stuff so I believe but it's the first time I've set it up 
like this.

Also the printer is now plugged into the server, so we can use it from either 
PC or the laptop, and I've got cron jobs set up to back up the large 
directory of music etc. files from the desktop to the server a couple of 
times a day, also the /home/ from the server to the desktop although I 
probably ought to arrange a weekly/monthly routine for this.

> 
> And just following on from the above, one can have a setup using a car 
> battery, and kept up to charge via a charger, plus a bit more fiddly 
> bits, to run your computer and therefore without the need for a PSU and 
> which would not only give you a stable power supply but also be immune 
> to power fluctuations or power failures (the latter in the short term of 
> course).
Sounds a bit like I heard Google is now doing with their servers - 
distributing DC rather than mains AC and having batteries scattered around 
the racks. I wouldn't connect a trickle charging car battery directly to this 
motherboard though - they tend to develop more than 12V under this condition.

What I have is an APC 1500VA UPS sitting under the desk that supplies 
everything, fed via a Belkin Gold Series distribution block that also has 
surge protectors for the phone line and the TV cable (my broadband is 
delivered via the TV cable). Where I live, though, the mains power is pretty 
reliable but it only takes one hit from an induced surge....

> 
> There is an article on how to achieve this but I would need to go 
> searching for it in my archives (seeing as how my friend, who has since 
> deaded himself by having a heart-attack and now cannot provide the info, 
> was using this process).
Shit happens, mate. My wife had MND, leading to the same end result. Let's 
just say it wasn't the most pleasant night I've ever passed.

At some stage most of us have to go from AC mains to low voltage DC. With the 
previous arrangement in this server I had a board that needed an ATX PSU. You 
just can't get these in a sensible power rating matching the requirements of 
low power machines like mine. The lowest rated unit I could get was 180W. I 
suspect the PSU was wasting nearly as much energy as the electronics was 
using, plus the cooling fan exhausted from the back of the case with the PSU 
air intake near the front of the case, resulting in a stagnant, overheating 
area over the motherboard. So I had to add fans to the "fanless" motherboard 
to stir the air around it.

Plus, I no longer have any redundant cables inside the case, so there's 
nothing to look untidy or impede air flow. The picture is of the fully 
completed machine. My son said it looks good so I used a sheet of 3mm acrylic 
instead of metal for the top cover.

With the new version, the PSU is rated at 40W, ideal for what I need. Plus the 
fan blows air IN at the back of the case, hitting the back of the PSU and 
creating a nice bit of turbulence over the processor heat sink, at least 
that's my theory and the machine appears to be perfectly cool and happy. I 
used a fairly expensive 60mm, 12V Papst fan which should run more or less for 
ever. At first it was blowing almost a hurricane through the case and making 
a lot of noise in the process. I cut the 12V line and inserted a zener diode 
to reduce the fan voltage->RPM->audible noise. When I consulted lmsensors it 
reckoned the processor core was running at about 30degC.

WARNING - PLEASE READ
I chose to use an open frame switcher inside the server case partly because I 
already had more than enough space in there, partly because I hate external 
in-the-middle-of-the-cable power supplies and wall warts. I am qualified and 
experienced in electronics, so I know how to read and understand the data 
sheet on installing the open frame switcher. It MUST be mounted with 
appropriate clearances, and it MUST be properly earthed. Plus if you touch 
the wrong end of it IT WILL BITE! So, if you're not absolutely confident that 
you know how to safely install one of these, don't even try. It's not worth 
the risk. The motherboard has a DC inlet on the back panel that can perfectly 
safely be used with a wall wart.


> 
> BC
> 
Dave


-- 

Registered Linux user number 393408