Monitoring power (and why I've ditched it)

A project log for Monitoring washing machines

One mans quest to spend less time in the basement

Lars KnudsenLars Knudsen 03/01/2016 at 15:223 Comments

In one of my earlier logs I proposed monitoring power usage of the machines, but after some research I've found that this is not a practical option (at least in Denmark where I am based). Current transformers, such as SCT-013-000 proposed by Gregor and similar models I've found all require that you break the outer insulation of your wire to expose the live or neutral wire. In Denmark (and I presume plenty other contries?) it is a legal requirement to have two layers of insulation on your wire, meaning such exposure is illegal.

If the clip went around the insulated wire then I'd consider it unobtrusive and it would be legal. This type of installation won't do. Picture by Calypso_rae

A practical solution to this could be to make a box in which the wires are exposed and the sensor mounted. The box would provide the second layer of insulation, making it a legal installation. However, personally I think this is to cumbersome and legally sketchy (and potentially really dangerous) to be a practical approach for this project, when the accelerometer data so far is really promising.

Another approach could be to hack a watt-meter, as seen here from the wattmote project, link below

Another option could be to buy a watt-meter, like Kill A Watt or similar but this falls into the same bucket as monitoring e.g. the lights on the washing machine. Different meters are likely to behave differently and I can't expect the same meters to be available to everyone, so it will be hard to make a general solution. Also, I think it might be even hard to hack a meter than to use a current transformer sensor. For examples of such projects see and

I might have overlooked options, be misinformed or otherwise mistaken. Please let me know in the comments if so :)


Prof. Fartsparkle wrote 03/12/2016 at 11:06 point

Hey, I've actually been doing exactly what you are trying to do here :)

I'm still doing the whole energy measurement and I've been pretty successfull. We can have a chat if you want, I did some more tests with op-amps with even better results than my last update showed.

Regarding the legal stuff with the cable. I just made my own cables with double insulation, you can get everything you need for that from a proper hardware store.

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Mads Chr. Olesen wrote 03/02/2016 at 14:35 point

Do you have a Kamstrup energymeter? If so can help monitor the power. The washing machine signature power usage should be easy enough to recognize. (Alternatively, you can get one installed as a "bimåler", they are quite cheap used.)

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Lars Knudsen wrote 03/03/2016 at 15:20 point

I don't have one as my main meter, which is what I think you are thinking of? Are you sure that it would be easy to recognize the individual machine signatures when I also might be running the dryer, dishwasher, water cooker, etc. on the same meter? Is there any examples of projects of that kind?

Under all circumstances, as I said, I'd rather make a solution which doesn't involve monitoring or hacking specific displays which might not be available more generally.

ps: Aalborg represent! :)

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