# Re: Call to ban petrol cars by 2040

• From: "Mortimer" <me@xxxxxxxxxxx>
• Date: Thu, 27 Sep 2007 17:04:39 +0100

"Depresion" <127.0.0.1> wrote in message
news:13fniu19ipk9j4d@xxxxxxxxxxxxxxxxxxxxx

news:1190904680.652721.195350@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

You are wrong too. I have actually measured the consumption of several
computers with a wattmeter. 125W is failrly typical for a desktop and
notebooks can be as little as 20W. The extra power supply capacity is
to allow for lots of optional peripherals.

Intel's latest "low power" desktop CPU is rated at 95w that leaves 30w for
you to power your MB,GPU,HDD,CDD and take into account the 70% efficiency
of a PSU. In other words once again you are talking total codswallop, the
question is are you just wrong or are you deliberately telling porkies?
The last PSU I remember seeing rated at less than 150w was on a first
generation Pentium and they were only 54% efficient. According to my
Laptop supplier the draw it places is 45w normally with a peak of 65w two

I've just checked the DC power consumption of my laptop from its charger,
and the results surprised me.

1. With a fully-charged battery in place and with the laptop running
normally, the current was just over 1A.

2. With no battery in place, so the charger is just powering the laptop, the

The no-load output voltage of the charger is about 20V - sorry, I can't
measure the on-load voltage because I can't put the testmeter leads across
the plug while it's in the socket, but I imagine the voltage will be fairly
similar since this is the rated output voltage.

So the laptop is using about 20*0.15 = 3W with the backlight, the CPU and
the disk, which seems very low. That's for a 1.8 GHz Celeron-M.

Trickle-charging the battery, even in fully-charged state, is drawing 1-0.15
= 0.85A so it's consuming 20*0.85 = 17W.

I can't be arsed to wait several hours to discharge the battery to see how
much extra current is drawn powering laptop and flat battery ;-)

Measuring the AC input is more difficult: I'm reluctant to rig-up Heath
Robinson wiring that will allow me to stick my ammeter into mains wiring.
Also, you need to take into account power factor (switched-mode power
supplies have a phase difference between voltage and current) and current
waveform which is probably not a nice simple sine wave so the test meter's
RMS reading will not be valid.

.

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