Date   : Tue, 01 Sep 2009 11:11:03 +0100
From   : zeem.uk@... (Alex Taylor)
Subject: Leccy @ Acorn World '09

2009/9/1 Rob <robert@...>:

> my laptop PSU proudly states "input
> 100-240V, 2.3A" (i.e. 230-550W) and "output ?19V 3.95A" (i.e. 75W)

Power consumption remains roughly the same for the device in use; if
the voltage is halved then the current doubles, and vice-versa. If
there's only one quoted maximum input current rating (2.3A) then it
must apply to the lowest voltage input. If the power supply consumes
2.3A at 100V when providing its maximum rated output, then it's only
going to need about 1A to do the same job at 240V. Basically, the
first figure you've given for the power is correct, it'll be a ~230W
power supply.

> The difference of at least 150W probably explains why it runs
> blisteringly hot most of the time!

I've had plenty of people I work with ask me about how hot their
laptop power supply runs; some of them have thought that they're
faulty. Not surprising if you're not familiar with devices that run
almost too hot to touch!

-- 
Alex Taylor