Re: gEDA-user: powermeter results!

[Stefan Salewski <mail@xxxxxxxxxxxx>]

On Sun, 2009-11-15 at 16:04 -0500, DJ Delorie wrote:

> was under by about 12% but it's close enough to get interesting data.

Really interesting and surprising?

I am sure that you build a really fine powermeter.

But my feeling is, that power meters are not really useful for smart
people. I bought a simple power meter some years ago (Conrad Energy
Monitor 3000, about 30$). It gave my nearly no surprising results,
always in the range of +-10% of my guessed consumption. Only exception:
My mother had an old video recorder, which takes 12 Watt for standby.
Really worse, my guess was only 5 Watt. Two years ago she buyed a flat
TV which had 100 Watt from data sheet. My hope was, that is not really
so much. But indeed, nearly 100 Watt. Her old cathode ray TV took only
55 Watt, but was a little bit smaller. Is this really progress?
What is most useful for measurement is standby comsumption, but for very
small values about 2 Watt and not Ohms loads measurement error may be
large. I guess for devices with small case my hand is more accurate: If
device remains cold (not warmer than ambient) consumption is less than 2
Watt in nealy all cases. This simple test did not work for the video
recorder, it had a very big metal case with good air circulation, so it
was impossible to feel dissipated heat.

Conclusion: In most cases you can guess the consumption or have the
value from datasheet. And even when you know that the device has more
consumption as it should (old washing/cooling machine, refrigenerator)
it is often not a good idea to replace it with a new one, while it is
still working. Building this new device and recycling the old one may
consume a lot energy too.

Sorry for this off topic post.





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