[CentOS] Power-outage

Robert Heller heller at deepsoft.com
Sat Jul 2 20:13:59 UTC 2011

At Sat, 2 Jul 2011 18:58:14 +0100 CentOS mailing list <centos at centos.org> wrote:

> On Saturday 02 July 2011 18:21:27 Jason Pyeron wrote:
> > > > > But surely computers actually use DC, so couldn't my
> > > > > torch-battery
> > > > > device just supply the PC components directly?
> > > > 
> > > > A PC uses several *different* DC voltages: +12, +5, +3.3,
> > > > and several
> > > > others and they need to be *precise*.  Some of these are
> > > > not an exact
> > > > multiples of the standard 1.5V Carbon-Zinc cells typicaly used in
> > > > torch batteries.
> > > 
> > > I wonder, how is this issue solved in laptops? They use only
> > > one DC battery, typically with a single voltage output, AFAIK.
> > 
> > (sorry ctrl-enter sends...)
> > 
> > Laptops, google mother boards, etc have power supply circuits on board.
> > Remember that a switching powersupply taking AC still has dc to dc
> > converters in it after the conditioning stage.
> So couldn't the OP then plug a battery "in between" (I'm talking in principle 
> here, not realistically) --- after the AC-to-DC stage but before the 
> "conditioning" stage?

The input DC side 'normal' switching power supply is like 100+ volts DC,
since it is just rectified and lightly filtered from the Mains.  And
short of completely tearing the PC's power supply apart and rebuilding
it, it is just not a trivial thing to do.

> If a laptop can have several *different* and *precise* voltages from a single 
> DC battery, why the desktop cannot?

In theory it could, it just does not need to. The AC vs. DC mains war
was lost like 100 years ago.  ALL main 'wall' power is AC, either 110 or
220, 50 or 60hz.  Since desktops (and servers) are meant to be 'plugged
into the wall', the power supplies of all want 110VAC or 220VAC (or possible
either) at 50 or 60hz.

> I am not saying that it would be easy or cheap, just that the above "different 
> voltages" argument seems false from my POV. If a laptop can be battery-
> powered, so can a desktop (given that you have all the hardware to implement 
> it). You don't need to tweak the motherboard, just the PSU. It's routinely 
> done in laptops, so it doesn't seem to be rocket-science or something too 
> expensive. I wonder why aren't there any desktops on the market with same 
> technology?

The closest thing is a 'lunch box': a desktop system you can carry. 
Although once you get there, you just plug it into the nearest wall
outlet.  In all 'moving' situations, AC power is available: Amtrak
trains all have 110V outlets at every seat. I imagine passenger
aircraft also have 110V outlets ditto for ships at sea or even RVs (in
both cases, hanging an alternator onto the engine is a trivial task).
Building a battery powered *desktop* (or server) just does not make
sense, unless you are Google (or the Army, Airforce, Navy, or NASA) and
want servers that are imune to power failures, in which case you just
custom build what you need.

The different voltages argument is not the argument against a battery
powered desktop, just that a battery powered desktop (or server) is a
non-trivial design.  One cannot just solder a pair of wires onto the
motherboard and connect them to some random battery.  One has to start
with either a motherboard *designed* to be connected to a battery (eg
a laptop motherboard or Google custom server motherboard) OR a power
supply meant to be connected to a DC (eg battery) power source.  I
believe there do exist ATX power supplies that are meant to be connected to
a DC power source (like a battery).  I expect that the *military* might
use such in some situations.  

> I'm using an UPS for my desktop system, but I don't need it for the laptop. If 
> the AC power drops, even for a moment, the laptop battery will kick in and 
> sustain the machine. I just think that the same thing can be implemented for 
> the desktop too. If I understood the OP correctly... ;-)

A laptop effectively contains its own UPS in the form of a power brick,
battery and power supply on its motherboard.

Yes, one *could* build a desktop or server that way, but why bother,
since AC wall outlets are everywhere one might want to use a desktop or
server? Anyplace where a power outlet is not available, you use a
laptop. A laptop is a special class (as is a smart phone or a tablet)
of system.  There is (in the SciFi world) the idea that someday
'desktops' in the current / conventional sense may completely vanish
from the universe, taken over progressably by laptops, tablets, smart
phones, wearable computers (motherboard == shirt, monitor == shades,
power supply == hat with embedded solar cells, virtual mouse/keyboard
via motion sensors in your shirt sleves/gloves, etc.), or even
implanted computers (eg as a thin circuit board between your skull and
scalp, and 'wired' directly into your brain).  This seems to already be
happening to some extent, in that laptops are becoming the computer of
choise and desktops are becomming an 'old school' sort of thing.

> Best, :-)
> Marko
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Robert Heller             -- 978-544-6933 / heller at deepsoft.com
Deepwoods Software        -- http://www.deepsoft.com/
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