
DIY quest for a 6 watt high-end desktop computer - ck2
http://ssj3gohan.tweakblogs.net/blog/8217/fluffy2-59-watt-high-end-desktop-computer.html
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ChuckMcM
This guy should totally go work in Google's platforms power group, they would
love him and give him better tools to work with.

That said, its inspiring to see folks tinkering at this level. I desoldered
the floppy connector on a motherboard so it would fit into a case once and the
guy who needed it was shocked that such things could be done successfully. I
was pretty amused until I realized an whole bunch of people who are really
bright technically have artificially limited themselves to just making changes
in software. That is too bad. Old PC's are really easy to get hold of and
great for practicing your rework skills, get an old Metcal iron off Ebay or
somewhere, a magnifying visor, and boom go to work.

The author didn't mention a weight limit but you can passively cool the CPU
with a copper heatsink on the back of that monitor, something like 9" x 21" of
copper fins has a lot of surface area to work with. Might save a bit of power
there too.

~~~
asdfs
>The author didn't mention a weight limit but you can passively cool the CPU
with a copper heatsink on the back of that monitor, something like 9" x 21" of
copper fins has a lot of surface area to work with. Might save a bit of power
there too.

He actually intends to do passive cooling, though I'm not certain his heatsink
is going to be large enough when the CPU is running at full load for an
extended period of time. You can see him discuss the casing and see the
planned heatsink here:
[http://www.youtube.com/watch?feature=player_embedded&v=S...](http://www.youtube.com/watch?feature=player_embedded&v=SmqtcvqXapI)

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ck2
His 8-watt i3 is also a great story:

[http://ssj3gohan.tweakblogs.net/blog/6112/85w-core-i3-based-...](http://ssj3gohan.tweakblogs.net/blog/6112/85w-core-i3-based-
desktop-computer-%28english%29.html)

~~~
gvb
Thanks for the link, it was _much_ more detailed.

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polshaw
whilst it is an impressive job, the title is misleading; it's 6W _idle_.. 75W
load.

~~~
mmphosis
I agree, the title is misleading. And, I see a big fan on the board.

The "low-end" Raspberry Pi, not including the monitor, draws a maximum of 3.5
Watts = 5 Volts DC x 0.7 Amps

[http://www.raspberrypi.org/phpBB3/viewtopic.php?f=2&t=50...](http://www.raspberrypi.org/phpBB3/viewtopic.php?f=2&t=5068)

And, RPI doesn't have a fan.

~~~
archangel_one
The fan looks to have been replaced in a later picture.

I've got a RPi here which is doing sterling service for several tasks, but it
certainly wouldn't be satisfactory for desktop use like he appears to want -
that machine is a Core i5, the two are lightyears apart! Plus the convenience
factor - the RPi won't power USB devices that want more than a minimal amount
of juice (an external 2.5" HDD, for example) whereas this machine could
happily drive them at a temporarily increased power draw.

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erichocean
Why is he not using a low-power Xeon? The 17 watt max TDP CPU is pretty
amazing.

We've got a server design in house using commodity parts for a three-server
cluster that's less than 60 watts per server. The whole thing (including AC/DC
conversion overhead) is less than 2 amps at full draw.

~~~
aristidb
These Xeons probably don't have a HD4000 graphics unit?

~~~
erichocean
Ah, good point. Obviously servers don't need that. :)

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legulere
> It needs to be completely silent. No fans.

You can't hear fans when they run at a very low speed. This will make your cpu
cooler and use less energy

~~~
andreasvc
It is my experience that any mechanical component will start to make noise at
some point. Better to avoid it altogether.

I don't understand why you say that using a fan would make the CPU use less
energy. On the contrary, the fact that a CPU requires cooling indicates that
it uses more energy than a CPU which doesn't (more energy converted to heat).

~~~
legulere
Electrical resistance is dependent on the temperature. The lower the
temperature of your cpu is, the less power it uses.

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hollerith
I like how the battery is integrated into the computer.

I think a typical UPS converts AC to DC and then back to AC. I wonder whether
this guy's design avoids those two conversion steps.

~~~
lutusp
That's easy to answer in general -- if a computer runs on line power, then it
has at least one AC -> DC conversion step. If it has a small, light, high-
efficiency power supply that doesn't require large 50/60Hz transformers, then
it converts twice:

120V AC -> 170V DC -> 20 KHz switching inverter -> 20 V DC.

So with respect to frequency it's 60 Hz -> DC -> 20 KHz -> DC. Yes,
complicated, but much more efficient than the old iron-core transformer days,
even though the latter involved fewer steps.

The step from 120 VAC to 170 VAC is an unavoidable increase because 120 VAC is
RMS voltage, not peak voltage, and the DC conversion yields the peak value:

Peak V = RMS V * sqrt(2)

It wasn't very long ago that 170V transistors were difficult to acquire and
notoriously sensitive to voltage spikes, but this problem is essentially
solved.

A computer that only ever runs on batteries may have one, or no, conversions,
depending on whether the battery voltage is exactly what the computer needs.

I speak as someone who has been designing electronics so long that my first
designs used vacuum tubes, and whose 20 KHz inverters flew on the Space
Shuttle.

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derwiki
Great read. I wonder why the author didn't go with something like the three
watt MK802 Linux mini-computer though?

~~~
ck2
I think the idea is he wants full processing power on demand while low power
for the 90% of the time it's at idle.

ARM is great for idle but is still a fraction of desktop cpu computational
power.

It's a couple years out of date but scroll down to the V8 and Sunspider
benchmarks here:

[http://vanshardware.com/2010/08/mirror-the-coming-war-arm-
ve...](http://vanshardware.com/2010/08/mirror-the-coming-war-arm-versus-x86/)

~~~
steevdave
The new quad core ARM boxes are actually quite good. My own personal use case
is different but as a Gentoo developer it's nice to see something like Firefox
"only" take 3 hours to compile. Which is really good when trying to debug
issues because an mx51 it takes 18-20 hours.

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3amOpsGuy
Incredible endeavour and i wish this catches on in a bigger way.

For now the average person can probably jump on this idea to some extent by
switching to a tablet where possible. I think the ipad3 is around 4.8watts
over a full charge discharge cycle with the charger unplugged after charging.

~~~
rm999
Isn't a laptop a better replacement? They are usually optimized for low energy
usage, and run a full OS.

How does the energy usage of this computer compare to say, a macbook pro?

~~~
Someone
<http://www.apple.com/macbook-pro/specs> gives 7 hours of WiFi use and 30 days
standby on a 95 Wh battery for a MacBook pro. So, it will be somewhere between
0.1-ish W and 13-ish W for idle state. I cannot find something better. For the
Mac Mini, <http://support.apple.com/kb/HT3468> gives 11W in idle.

~~~
doublerebel
FWIW I consistently get 11-13w at idle, 7 hours battery under use from my
Samsung Series 7 Chronos i7. Obviously Samsung takes cues from Apple but I'm
pleased at half the price.

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hollerith
I notice his choice of motherboard conforms to the _thin_ mini-ITX
specification introduced last year by Intel.

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ricardobeat
What exactly is a _voltmod_?

~~~
ANTSANTS
Modifying a hardware component to feed it more or less voltage. Particularly
zealous overclockers may overvolt components to allow them to run at higher
clockspeeds. Particularly zealous efficiency nuts may undervolt components to
trade decreased performance for decreased power consumption.

~~~
Someone
In both cases, part of the trade typically also is reliability. The farther
you go outside of the spec for parts, the higher the risk that they work only
sort-of. I gues that, if money wasn't a problem for this guy, he would have
bought ten different CPUs and checked which one kept working at the lowest
power.

