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727 posts

Ultimate Geek
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Topic # 97887 21-Feb-2012 19:18 Send private message

After an upsurge in my power consumption over the last few months I thought I'd better see about tracking down where it was going.  I've got an inexpensive "power meter" that goes in-line and measures things like instantaneous, cumulative, and peak power usage, voltage, power factor, etc.

I'd recently put in an AV receiver, so I thought I'd start with my HT set up.  Everything goes to a zap catcher and from there via the meter to a power point. My total standby usage was about 65 W - high I thought.

I did a systematic survey - here's how it breaks down:
The zap catcher itself, and the ethernet switch - negligible, as expected.
My Vu+ Duo PVR - 20 - 27 W (I keep this in a heightened state of readiness as I often access it via my LAN, so standby can use almost the same power as "on", which is about 27 W also; it's a bit variable depending on whether the internal disc is sleeping.)
BDP - 3 W - higher than expected, but not outrageous
VCR - 2 W - not bad for such an old machine
Onkyo 609 - negligible

... but the kicker ...
Panasonic 50V20 plasma - this is on standby mind you: 27 - 38 W!
Even when I popped the power button - 27 W.
All it should be doing is lighting one LED on the front panel, and keeping the remote receiver warmed up.  27 W.

I checked the specs in the User's Manual:
"Standby power consumption: 0.4 W".

I don't think so, Panasonic.  Would you believe 90 times that?  Something seems very fishy here.

Calling them wasn't too useful - a long wait listening to advertising, then a person who told me that their results were "lab tested", and I shouldn't trust my consumer-grade device which could show slightly more (Um, excuse me - how would an increase in 0.4W translate into a reading increase of nearly 40 W in a device that wasn't complete junk, and how is a 100-fold increase, "slight"?), who then transferred me to a person who wasn't there and whose voice-mail message said they wouldn't be back until November!

I emailled them, but then I bethought myself of my GZ brethren (and sistren too).

So, ranting aside, and seeking a reality check, does anyone else have a power meter and a 50V20 or similar who is willing to run a few tests to see if my results are typical?

Maybe my set is faulty, or the technical specifications are at best, dubious, if not downright misleading, or maybe there is a "gotcha" - having a LAN cable plugged in, or a change in the current firmware that increased standby power usage beyond that with which the "official" testing was done, or something else.

27 W may still not seem like a lot, but compared to the 0.4 W specified, it would add $300 to my power bill at today's prices over a 5 year life span.

Any input?




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1370 posts

Uber Geek
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  Reply # 584815 21-Feb-2012 21:05 Send private message

I don't like to keep any more than is necessary powered up when I'm not using it, particularly when I'm out of the house (cumulative power draw, and the (admittedly minimal) fire risk from leaving lots of stuff running etc). Since many bits of kit, including my TV, only have standby rather than an actual power switch, I use a low-tech solution.

All my kit runs off two power strips (the sockets on which are individually switched for more control). One is for the minimal amount of equipment that I want to run all the time (mainly the sky box and DVD recorder for scheduled recordings), and the other has stuff than only runs when I'm actually using it (TV, WD media player, sound system etc). I just switch the second one off at the wall when I don't want to use stuff - power draw zero.

The Tivo should be in the "always powered list", but is largely kept powered off at the moment - there simply isn't much content on Freeview that I actually think is worth recording to watch.

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  Reply # 584825 21-Feb-2012 21:20 Send private message

The cheap power meter commonly sold in hardware shops for around $30 seems to be unreliable with non-resistive loads. I had exactly the same experience with a Panasonic plasma, but when I did a more trustworthy measurement by different means, I found the consumption close to spec.



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Ultimate Geek
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  Reply # 584835 21-Feb-2012 21:43 Send private message

The meter I have was indicating 100% power factor during my tests. Doesn't that mean the load was effectively resistive?

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  Reply # 584840 21-Feb-2012 21:55 Send private message

It would if the power factor measurement was reliable. It's quite a long time since I did this but I clearly recall a reading of about 25-30W from the hardware store meter. I believe I checked RMS current with a (true RMS) multimeter to arrive at the conclusion that the Panasonic spec was credible. But I'm sure someone else out there with better equipment & experience will be able to cast more light on this than I can.

gzt

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  Reply # 584865 21-Feb-2012 22:28 Send private message

Which meter are you using exactly?




Energy saving and monitoring devices available in NZ: www.energymonitor.org.nz



727 posts

Ultimate Geek
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  Reply # 584869 21-Feb-2012 22:33 Send private message

gzt: Which meter are you using exactly?

It's an ELTO brand one. I can't see a model number.

gzt

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  Reply # 584877 21-Feb-2012 22:46 Send private message

There was a discussion here a while ago where a guy got a 69W standby figure for a microwave using the Elto. That was not rechecked with anything else but it seems unlikely.



727 posts

Ultimate Geek
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  Reply # 584885 21-Feb-2012 22:59 Send private message

27 W for a TV seems unlikely too, and that is the cause of my concern. Something is amiss somewhere: the TV, the specification, or the measurement. My trilemma, I guess that's the word, is which.

At the moment, my money is on the specification.

gzt

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  Reply # 584892 21-Feb-2012 23:18 Send private message

xarqi: At the moment, my money is on the specification.

My money is on the meter reading incorrectly. My guess is there is not enough processing power in there to correctly calculate wattage for badly corrected switch mode power supply loads which are not consuming in a nice predictable sine wave pattern.



727 posts

Ultimate Geek
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  Reply # 584896 21-Feb-2012 23:37 Send private message

I'm thinking that at the end of the day, the only way I'm going to know for sure is by somehow laying hands on a meter of unimpeachable repute. That sounds like an expensive proposition, although hiring one may be feasible I guess. I don't want to blow a year's potential savings on the rental!

What brands would be considered reliable?

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  Reply # 584897 21-Feb-2012 23:49 Send private message

I have a Panasonic 50VT20 and one of those little meters... Unfortunately it's currently (ha!) on an active computer. When I next need to reboot that I'll move it to the TV and test if I remember...

My money though would be on not being able to measure accurately at that low level.

Cheers - N



727 posts

Ultimate Geek
+1 received by user: 7


  Reply # 584906 22-Feb-2012 00:49 Send private message

Talkiet: I have a Panasonic 50VT20 and one of those little meters... Unfortunately it's currently (ha!) on an active computer. When I next need to reboot that I'll move it to the TV and test if I remember...

My money though would be on not being able to measure accurately at that low level.

Cheers - N

Thanks for that; I'll look forward to a report at your convenience.

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  Reply # 584908 22-Feb-2012 01:18 Send private message

Cant you do this with a multimeter and just check the voltage and amperage?

Volts x Amps = Watts ?

We can safely assume that the voltage is 230-240 so it sould be less than 100mA being consumed on standby?




Ray Taylor
Taylor Broadband (rural hawkes bay)
www.ruralkiwi.com

There is no place like localhost
For my general guide to extending your wireless network Click Here






727 posts

Ultimate Geek
+1 received by user: 7


  Reply # 584909 22-Feb-2012 01:37 Send private message

raytaylor: Cant you do this with a multimeter and just check the voltage and amperage?

Volts x Amps = Watts ?

We can safely assume that the voltage is 230-240 so it sould be less than 100mA being consumed on standby?


I think it gets a bit tricky with AC current.  I'd need a proper RMS meter I think, and I'm not sure the ancient analogue multimeter I have would be reliable.  Or safe!  I'm a bit leery of putting it in series in a mains circuit as I'd have to.  Chances are good I'd give myself a belt or upset the attached electronics by making an intermittent contact.

There's also the power factor to consider, and while we could maybe assume that to be 100% (as my in-line meter claims it to be), maybe it isn't.

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  Reply # 584911 22-Feb-2012 01:50 Send private message

Thats a good point.

An electrical supply store like ideal or coreys sell industrial / electricians mains voltage multimetres. A specialised electrician should be able to loan you one if you know someone like that.

However i dont know about the AC part


Basically you switch off the appliance using a power switch on a 4-way power strip. Insert the meter between the wall socket and the power strip, then switch on the power switch once the multimeter is in place.





Ray Taylor
Taylor Broadband (rural hawkes bay)
www.ruralkiwi.com

There is no place like localhost
For my general guide to extending your wireless network Click Here




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