In article ,
writes:
Is there any cheap/easy way to measure the power consumption of mains
powered equipment that consumes a few tens of watts and is almst
certainly non-sinusoidal? In particular I want to measure the power
consumption of a (hopefully) low power PC that should be consuming
around 25 watts.

A cheap plug-in power meter (a Brennendal one) claims it's consuming
about 50 watts but I'm not at all convinced it's telling me the truth.

I found the Brennendal one to be very inaccurate. It was suggested
to me that this happens if you don't fit batteries in it, but I
never got around to seeing if that was the case.

I know 'proper' power meters are expensive and I don't really want to
spend lots of money, nor do I really want a very accurate answer. If
I can just confirm it's consuming something between 20 and 30 watts
I'll be happy.

Simply buy a different make. AFAIK, it's only the Brennendal which
is very inaccurate. Get one which can give you the power, VA, and
power-factor readings - it's likely to understand the concept of
non-sinusoidal current loads.

I also still have one I made about 30 years ago, before the cheap
plug-in ones appeared.

BTW, some time ago, I wrote a blog on the significance of power-factor,
which you might find interesting, with some java applets you can play
with changing various parameters and see what the effect is...
http://blogs.sun.com/agabriel/

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]