| Jordan Hazen 2007-05-23, 3:25 am |
| In article <1179601502.816210.224140@k79g2000hse.googlegroups.com>,
Eric <egrumling@gmail.com> wrote:
>I am in the process of converting my ham radio "server" pc to solar
>power. It is currently used as an APRS gateway and an Echolink radio
>link. It can run for days without spinning up the hard drive and I may
>be able to underclock it to get rid of the CPU fan. I know it still is
>unlikely to be as efficient as a laptop, but I'd rather not buy more
>than I need.
>
>http://www.mini-box.com/PicoPSU-120...c=8&category=13
>
>The above link points to the one I'm looking at buying. Size is not a
>factor, but the concept of a connector sized PSU is interesting.
>
>Anyone have experience with solar powering a desktop PC?
Yes, I've been running my always-on router/firewall/Asterisk machine
on native 12V for a couple of years, and recently converted my main
workstation as well. Both use "M2-ATX' power supplies, which are very
similiar in design to that PicoPSU you're considering.
These work very well, for the most part (so long as the computer isn't
too much of a power hog-- P4's and most Athlons need not apply  , and
are significantly more efficient than DC-AC-DC through an inverter.
The router box pulls about 25-30W, a bit over 2A at 12-13V. It has
VIA C3 CPU (Nehemiah), originally at 1 GHz but underclocked to 500 MHz
at 1.5V Vcore, on a generic Pentium III-style motherboard with 256MB
RAM, basic S3 onboard video (always in text mode), four low-end
Realtek Ethernet cards, and four serial ports.
It uses a Compact Flash card in lieu of a hard drive, and runs
completely fanless and silent, with no moving parts at all.
The attached Ethernet switch, DSL modem, and two Wifi bridges are also
native 12V, and add another ~1A total. The monitor is an 12V, 9"
monochrome CRT, originally part of an NCR cash register. It's a bit
picky about its voltage and won't start up at much over 13V, but an
inline diode takes care of that, and can be bypassed when batteries
are low. This monitor draws a little over 1A at 12V, less than any
desktop LCD I've encountered.
The other 12V computer has an Athlon 64 (Socket 754) motherboard,
fitted with a 2 GHz Turion MT-37 laptop CPU , 2 GB RAM, one 500GB SATA
hard drive, and a few PCI cards (video framegrabber, satellite tuner,
MPEG decoder), but relatively low-end video by today's standards
(Matrox G450 dual-head). It pulls just under 50W at idle (~4A),
rising to 70-75W under load, at full speed... fans are
temperature-triggered and only come on at sustained high load. Newegg
had the Turions on sale recently for about $60. I've heard that some
types of normal Athlon 64s can do almost as well after undervolting,
though.
When fitted with an AC power supply (Seasonic 300W, supposedly ~80%
efficiency), the Turion drew 60W at idle, rising to 90W under load...
not counting any inverter losses.
Even when my DC system is running from grid power (via RV converter),
there's a net power savings of about 5-10W from running the 2nd
computer on 12V, vs. direct AC. The M2-ATX (and PicoPSU) are rated at
about 92-94% efficiency.
One potential problem with these DC supplies is that they tie your
PC's ground to the negative battery terminal, which can cause
ground-loop problems-- audio noise and other issues. Improving ground
connections helped some, but I had to add some inline ground-loop
isolators from Radio Shack to completely eliminate the noise.
There's also an intermittent flicker issue on one of the monitors (a
Viewsonic VA520, 15" LCD, ~2A at 12V), which may also be ground-loop
related... still troubleshooting that.
Transformer-isolated DC-DC supplies do exist, but are significantly
less efficient, usually down in the 75% range. Most telco 48V
supplies are of this type.
Anyway, with these small DC-DC PSUs and careful component choice, it's
possible to get close to a laptop in power efficiency. The desktop
does suffer small power losses from things like linear voltage
regulators on the motherboard (for the RAM, Northbridge, AGP), PCI
cards that have high idle draw and can't be shut down without putting
the whole computer to sleep, etc.
--
Jordan.
|