Wireless Electricity Meters


Efergy Wireless Electricity meter

Efergy Wireless Electricity meter

I am a big fan of wireless electricity meters – they make electricity consumption visible. And if you are trying to reduce your electricity consumption they are a fantastic tool. I bought one of these units a couple of years ago but it had no memory. So earlier this year I overcame my reluctance to buy another piece of consumer nonsense and bought this Efergy unit. It keeps track of the last 7 days energy consumption in memory and so I can plot a graph showing the household electricity consumption day by day.


My Electricity Consumption for 2009

My Electricity Consumption for 2009

The graph is remarkably dull. The 7 day average plummets when we go away (but why only to 5 units a day is a mystery to me) and we have weekly peaks in consumption when we do washing and tumble drying. Surprisingly I haven’t seen much evidence of a dependence on day length yet, but I expect that will begin to show up soon. However despite their usefulness for plotting variations in electricity consumption, the thing I wanted to highlight was the poor accuracy of the units.

As I write my Electrisave meter says I am currently using 0.6 kW while my Efergy meter says I am using 0.55 kW. This 10% discrepancy is typical, and not always in the same direction. In fact this is within specification for the units which only claim 10% accuracy. Because it has memory, I can test the performance of the Efergy unit against the EDF energy meter that determines how much I pay. Since July when I began the comparison, the Efergy unit under-reads by between 15% and 25% depending on exactly which period I compare them. I think this is because the units’ sensors read only the electrical current and the energy consumption depends on the relative phase of teh current and voltage. For households using lots of low energy light bulbs (for instance) the phase can vary significantly. I don’t think this really detracts from the utility of these devices – but it is perhaps worth bearing in mind.




5 Responses to “Wireless Electricity Meters”

  1. Jeff Says:

    The poor accuracy surprises me. I wonder what the accuracy of the billing meter is. Our billing meter is a small box with a digital display, so I assume that it is a current transformer and works like the ones you have bought, and so may be of similar accuracy. 10% of my electricity bill is not insignificant.

    I note that these devices boast of a 15% saving – that is the same order as their accuracy. Hmmm.

  2. Jason Says:

    The billing meters are very accurate. I work for an electricity company. We have about 800 000 customers who would average about 2 meters each. We get plenty of complaints from customers who are sure their meter is wrong. (one of competitors has an actor in their advert say “You could be being ripped off, I know we were”, imagine how many complaints that generates…) The company has been around in it’s present form for about 10 years, so we’ve accumulated reasonable experience. While there have been many billing errors, not one single complaint (or sheduled random sample) has ever revealed a meter reading high. While lack of proof doesn’t prove lack, I can’t imagine any failure mode in which the meter would read high. The disk is driven by induced eddy currents proportinal to the power. The disk is retarded by passing through a permanent magnetic field. The drag on the disk is proportional to the speed of the disk. Hence the speed of the disk is proportional to the power used. The only ways for it to fail would be for the coils to aquire more turns, the aluminium disk to decay into a different element or the permanent magnet to fail. The only way for the magnet to fail would be for it to be heated enough to randomise the domains within. By the time it reached that temperature the meter (and the house it was attached to) would be charred to a crisp.

    The mystery of the 5 kWh used while away is generally explained by the fridge and freezer. They use between about 2-6 kWh/d when there’s no-one home.

  3. roger Bassett Says:

    Hello Sir, very interesting article. I work for efergy Technologies Ltd as the Product Support Specialist. 10% inaccuracy is the maximum you should see with our monitors but not ideal for customers such as yourself. 25% is a long way away. There are a few things we can try to increase your accuracy. On average our customers will see around 95% accuracy leading up to 100. The main reason for inaccuracies is due to the placement of the sensor and interference.

    We have a new and exciting product which reads the LED pulse on a electricity Meter. The IR sensor would give you very close to if not 100% accuracy.

    If you have a meter which has an LED pulse than we would be happy for you to test one of these units.

    For us you are the ideal person to test it as quality control is our number 1 priority. We are still a young company and any feedback good our bad will only make us better.

    When you have time mate can you give me a quick email. My email address is roger.bassett@efergy.com

  4. Efergy e2 Wireless Electricity Monitor « Protons for Breakfast Blog Says:

    […] while ago I reviewed a previous Efergy wireless electricity meter and commented on its usefulness, but noted that the unit wasn’t very accurate – it was […]

  5. meyeroimz.livejournal.com Says:


    Wireless Electricity Meters | Protons for Breakfast Blog

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