On Tue, 16 Feb 2010 07:06:35 -0800 (PST), Jim Wilkins
wrote:

On Feb 15, 11:57*pm, "Michael Koblic" wrote:
...Kill-A-Watt ...
My most recent purchase (Compaq Presario) does this:

Turned off 2.1W
Booting 60W
On but quiet 46W
Asleep 5.8W
Hibernating 1.7W

My old computer also draws about 3W while supposedly switched off.

So the questions a .......
--
Michael Koblic,
Campbell River, BC

In a discussion on alt.energy.homepower someone (Neon John?) wrote
that they had tested a Kill-A-Watt against lab equipment and found it
quite accurate, but like any digital instrument you can't trust that
the accuracy is as good as the resolution. If the 0.01 Amp display
resolution matches that of the A/D converter (doubtful) then the
wattage at 120V would change in steps of 1.2W and the real accuracy is
no better than +/- one step.

Switching Mode power supplies are going to throw a monkey wrench in
those accuracy tests. You have to test for that specifically.

1) Why is the computer drawing any power at all when turned off?

The circuit that commands the computer to power up when you press the
momentary-contact power button has to draw some power itself. I
believe they were designed for lowest cost rather than efficiency. The
service manual for my Dell Dimension says to press the power button -
after- unplugging the AC cord to discharge a large capacitor, before
swapping parts.

You are also supplying power to the Real Time Clock chip so you
don't run down the lithium battery on the motherboard, and the LAN
card and it's "Wake On LAN" circuit used on certain industrial use
machines - print spoolers and the like.

Some computers are also set up to power-up or wake-up when the phone
on the modem rings, or power the modem and answer the line while the
computer is still booting/waking. So it can sleep or hibernate and
still be used as a fax machine, or be remotely polled at 2 AM in a
business setting.

2) Why is the power drawn less when hibernating then when switched off?

See above. Your 2.1W and 1.7W readings don't really mean that much
unless you have checked the calibration of that KAW somehow, like with
a resistor load. Which I don't suggest. Even if you do the cheap
methods of converting 120 - 240VAC to a small amount of low voltage DC
can have high power factors.

It's a switching-mode power supply, and you might be getting
anomalous low or high readings at those low power levels. Do a little
research on "Q Factor" where power panels with large numbers of
computers burn up the neutral wires and the busbars in the panels.

The power supplies take little nibbles out of each cycle and the
cumulative current on the neutral is higher than the power phase draw
- they don't balance out like normal phase-neutral loads, because each
computer is taking it's nibble at a different moment in the cycle.

More prevalent on 120/208V 3-phase panels. They make special panels
and special "High Q Factor" 480V to 120/208V transformers with
double-sized neutral bussing to handle this. And you double-up the
neutral conductors or bus-bars between them.

3) What happens to a computer which is turned off and the plug is pulled?
The front-panel button won't turn it on until you restore AC power.

I have a main power strip on the side of this table that cuts off
everything, slays the energy vampires. (OK, I'm a fan of Joss Whedon's
work). The UPS and laptop charger are plugged into it, and sometimes a
soldering iron and small heat gun. The two desktops are on separate
strips plugged into the UPS. To use one I turn on the main strip, then
the UPS and let it self-test, then the strip for that computer. Their
monitors, USB drives, speakers, printers and keyboard lamp more than
double the power demand.

All well and good, but you'll be changing the CMOS battery more
often. Better than the old days, when the battery was molded into the
RTC chip, and you have to replace the whole thing.

Okay to kill the power totally to all the other peripherals, but
leave the computer itself plugged in. Plus, you want it to be turned
on overnight at least once a week - especially on Patch Tuesdays, when
Mickeysoft tries to plug all the holes.

I just let it run, they seem to live a whole lot longer that way. So
it costs a few pennies a day, big whoop.

4) What happens with laptops? Do they draw power from their battery
continuously even when turned off?

This Latitude doesn't, the batteries stay at 100% when it's shut down
or in hibernation. Standby does use some battery power.
I recently had to replace the 2032 CMOS batteries in my 10-year-old
Compaq laptops. Their main batteries are dead so I run them off AC and
they wake up from hibernation with no battery installed, usually the
instant I plug in the charger. Ergo they must not need battery power
in hibernation. The only symptom of the dead CMOS battery was the 1980
date.

They use a tiny bit too, but they have better power management.

-- Bruce --