D-I-Y power meter for entire house

[Simon]

Hello -

Having just received an electicity bill, I'm wondering whether anyone tried building a power meter for an entire house? In other words, something that would give an instantaneous digital or analogue read-out of the power being used by the whole house, without the need to squint at the spinning dial in the electricity company's meter (which is outside in my case).

I'm thinking of something like a clamp-on ferrite core around one of the incoming cables close to the meter, with a secondary winding driving a high-impendance panel meter of some kind, or perhaps a D/A convertor attached to a PC. A simple amplifier circuit might be required. Presumably for a typical house the overall load would be close to resistive, so measuring current alone would be sufficient. It would be fairly easy to calibrate the DIY meter, using the electricity company meter.

I haven't done the sums yet, but it seems like it ought to be feasible, but I can't find much evidence that anyone else has done it, nor can I find any consumer units with this feature built in.

[John]

Something like this?

"sensors clip directly onto your existing electricity meter's cabling"

John

[Simon]

Thanks, that gives me some ideas. The manufacturers have a website at

've just found a DIY example at it sounds like he only gets 1mV output per amp of current into the house from his clamp-on cores, so the job would not be entirely trivial. If my electricity company meter was inside, I would try pointing a cheap webcam at it and writing a bit of image processing software to extract power figures - it's surprising how effective this approach can be.

[Jonathan Schneider]

Somebody else suggests a webcam but it would be simpler to blue-tac something to monitor the flashing red light that most modern meters have. I've been thinking about doing this myself lately. Of course it won't be using a PC because that would be unreliable and burn more electricity that the information might be worth. However it does involve production of a small unit to count the flashes in a non-volatile way. Kind of like the meter does itself.

Jon

[Mike Harrison]

A small LCD counter module (e.g. RS Components 337-7151), with a phototransistor would probably do the job.

[AJH]

phototransistor would probably do

My solid state meter flashes at 1000 imp (impulse??) per kWhr. If each flash was logged as a date and time, via a usb port to the pc as a text file, then it could be viewed in Excel/Oo as a chart showing peak usage.

AJH

[Andy Hall]

This is interesting, but will it make you take an action when the rate of use is higher than you think it should be?

[Andrew Gabriel]

have to make assumptions about the voltage and power factor to estimate your power draw. I suppose it could be capacitively picking up the voltage waveform too, which could be used to help estimate the power factor, but I can't imagine that would be any good to accurately obtain the mains voltage.

In France, new meters for 10 or more years have been digital, and you can cycle through about 8 readings on them, such as kWh, current, peak current (not sure over what period), voltage, power factor, power, and probably more I've forgotten. No one ever comes to read it -- it's read remotely. You could try asking EDF to fit a french meter for you;-)

[Simon]

I think it would. I almost felt physical pain when I opened my electricity bill yesterday. Electricity charges have risen sufficiently that it's now worthwhile for me to put some time and money into reducing usage. Thanks for all the suggestions so far. As my meter is a 20-year-old spinning disk model in a cramped exterior box, my options for optical sensing are limited, so I think some kind of inductive measurement will be required.

[Dave]

Know what you meant (See my Powergen 10% + 30% on this ng.) It's not only the magnitude of the increase, but the frequency :-)

[<me9]

My current meter is 53 years old, with pointers that go round althought the house isn't quite 30. The original (digital mechanical) meter was replaced by the electricity supplier about 10 years ago -- because the original one was too old.

[Peter Parry]

Optical sensing on old meters is quite easy as they have a nice black band on the disk. I made such a device many moons ago using that well known optical transistor the OC72 with paint scraped off and a pea bulb as a light source.

[MikeH]

Yeah, it's the frequency that hertz doesn't it :-)

Mike

[Harry Bloomfield]

on 29/07/2006, Simon supposed :

The instrument is called a clamp meter and has been around since (?)....

You squeeze an arm which opens the jaws and permits it to be clamped (hence the name) around a cable. The display shows the total current being consumed. The used to be analogue but most these days are digital. You just clamp it around one cable only, either live or neutral will do - but not both as the current in one would cancel out the other.

[Bob Eager]

I have one here that I've owned since about 1966.

[T i m]

And my fairly old one reads DC as well. Handy to note my EV pulled

400A on takeoff and 200A cruising ;-(

All the best ..

T i m

[Owain]

September 1950, the Clamp-on Inductive Ammeter, patented by Pyramid Instrument Company, Long Island, New York.

[Grumpy owd man]

.addendum

You can get ones that go around the sheathing of 2 or 3 core cable +/or flex. We use them all the time [sorry for the rather long link]

[Andrew Gabriel]

MC1495L 4-quadrant analogue multiplier to form the instantaneous product of the voltage and current, just like I did in one I built in the early 1980's. Trouble is that this chip is obsolete for 20 years now, and no one produces a 4-quadrant analogue multiplier chip with differential inputs, which is what you really need for this task. I suspect most true power meters nowadays work buy sampling the voltage and current and multiplying digitally.

[Andy Hall]

Ohm my goodness, we're off on this cycle again... Watt will become of us?