Measuring Power used in Household appliances.

I would like to measure the amount of power used by a few of my appliances at home, mainly the total draw on some of my extension blocks. I’ve looked
at a few of the plug-in power meters you can buy for £20 or so but have seen a few people saying that these are not very accurate. So what would be the best (most accurate) way of measuring? Should I look to get a clamp meter instead? I’m not looking to spend a fortune (£100 maximum) but would rather get something that is fairly accurate than waste £20 on something that isn’t.
Thanks
Gav
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Gav wrote:

The plug-in ones are accurate enough for most purpose. They can give misleading results for some loads, it is true. But those /tend/ to be devices that don't add significantly to most household's electric bills.
A (current) clamp meter will not give an accurate measurement of power - only a true wattmeter will do that. Whole house "energy saving meters" will tend to suffer from the same (but generally insignificant) errors as a clamp meter. Which is mostly what they are.
The most accurate (and not too expensive) way is buy a second hand regular house electric meter and wire that (with due regard for insulation and safety) into an extension lead. It will give you a definitive answer to how much electricity is being consumed and will form part of the utility bill.
-- Sue
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A couple of issues:
You haven't said what you intend to do with the data you collect and that will have an influence on appropriate instrumentation. For example, you may have a difficult time with appliances that cycle, such as dryers, ovens, ranges, irons, toasters, water heaters, air conditioners, and to some extent, lights. To make sense of power consumption, you will want to note the approximate duty cycles of each of these appliances. Collecting this data can get complicated.
The house electric meter is a good idea. But even better may be using the one you already have. If you can keep your electrical load constant for some period of time, say 10 minutes, and then turn on the appliance of interest for ten minutes, you can observe actual real power consumption of the appliance on your own meter. No need to buy a second one. Not only will that be sufficiently accurate for your calculations, but it will take duty cycle into account over the measurement period, which may be what you are really after.
Chuck
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snipped-for-privacy@nospam.at.all says...

The $25 variety watt/watt-hour meters, such as "Kill-a-Watt" or "Power Angel" work perfectly well for almost all loads (can't think of one they wouldn't). I've have on on my TV for about two months (492kWh). It's there because it's the last place I wanted to measure power. ;-)

The plug-in variety are far easier to use and also take into account cycling. 240V lash-ups are a little more difficult though.
-- Keith
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| The plug-in variety are far easier to use and also take into account | cycling. 240V lash-ups are a little more difficult though.
If they would make one of those Kill-A-Watts for NEMA 6-15, 6-20, and 14-30 maybe people would not have to lash up anything. OTOH, such things should be made a standard for a few things like electric water heaters (that is, built in to the unit).
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snipped-for-privacy@ipal.net says...

Maybe not standard, but available. Since they can be had for $20- $30 retail, one-seys, it couldn't cost much to add to major appliances/money-sinks. My guess is that almost all the hardware needed is already in high-end ovens (the only thing I can think of that already has a display).
--
Keith

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These devices are surprisingly accurate, within a few percent in most cases. The next step up is a real power analyzer but these start at around $2K last I checked. A clamp meter will be less accurate, and you won't get the ability to measure power factor or cumulative kilowatt-hours which are two very useful bits.
The most meaningful results you can achieve are with the electric company meter on your house. There exist devices which attach to the outside of the meter and bounce light off the rotating disc to monitor power consumption in real time. It looks like you're in the UK though, and the UK power meters I've seen are bizarre looking things compared to what I'm used to, I don't recall if they have a visible disc motor in them.
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