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| On May 23, 12:19 am, j...@VictorTangoEleven.net.invalid (Jordan Hazen)
wrote:
> In article <1179601502.816210.224...@k79g2000hse.googlegroups.com>,
>
> Eric <egruml...@gmail.com> wrote:
>
>
>
>
> 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.
Thanks for the comprehensive answer. I think I'll be better off
looking for a used P-III laptop than trying to adapt the desktop,
mostly due to the video card. It is an ATI All in Wonder Radon, and
I'm sure it takes a lot of power to run (it is hot and has a fan on
the chip). I might still try this for my main PC, which is only on for
a few hours a week, mostly during daylight hours except in winter.
Either way it is an interesting project.
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