CT sensor inside a plug socket?

I'd like to monitor the power consumption at individual power sockets throughout my house. My idea is to fit an emonTx to each socket. I need to be able to fit a CT sensor between the socket and the plug of the appliance which is plugged into it.

I know that socket power monitors exist, e.g http://www.maplin.co.uk/plug-in-mains-power-and-energy-monitor-38343 but I wonder if any exist which have an output which would plug into the emonTx. 

Can anyone help?



Robert Wall's picture

Re: CT sensor inside a plug socket?

You're not the first to ask this. I've never seen anyone report that they've done it.

The difficulty will be making the connection to the outside world. Provided everything is inside an enclosure and double insulated, safety is pretty much assured. If you then make a galvanic connection, it becomes a major issue. That is the real obstacle.

Most look towards mounting an emonTx in a small box with a plug on one side and a socket on the other. The enemy is the need for personal safety when you're programming and testing a device such as this. In order to have a small enclosure, you need a very small dual-secondary transformer for power and voltage monitoring, or a direct connection to the mains for the power supply and for the voltage monitor. Current isn't so bad, you can get fairly small ring-core c.t's that are quite a bit smaller than the split-core ones. Once you have mains inside, the enclosure needs to be earthed metal (obviously not possible because of the need to get the radio out) or double insulated, and if you have a direct mains connection you can't work on it for testing unless you isolate all connections (in practice that means a 240 V isolating transformer) but even with transformers, there are still potentially lethal voltages around.

Decoding the radio transmissions of proprietary devices has also been mentioned, but again as far as I know, no-one has done it.

donturner's picture

Re: CT sensor inside a plug socket?

Many thanks for this, useful to know. I will consider hacking a proprietary device to see whether I can either 1) decode the signals it sends wirelessly, or 2) add wireless to it so I can integrate it into my existing system. 

The idea here is to create a virtual 'heat map' of each room's electricity consumption and potentially alerting me if the usage seems high (e.g. if I've left something on which shouldn't be on). 

calypso_rae's picture

Re: CT sensor inside a plug socket?

Building a self-contained unit which detects the amount of power flowing through it and transmits this info via RF is straightforward enough.  But equipping a whole house in this manner would be quite an undertaking.  Fixed appliances, such as lighting, would not be included by this means.  There might also be transmission difficulties, e.g. from the socket that's behind the fridge.

An alternative approach might be to monitor each of the final circuits at the Consumer Unit.  This would allow more channels of the emonTx to be used.  Trystan recently put some 4-channel power-monitoring code of mine onto the emonTx Github zone, along with a simple receiver sketch. 

A more refined version of this code, which uses all six of the Atmel's analog inputs, can be found on this thread.  At present, that code is configured to continuously monitor power on four channels, two on each phase; but could be easily changed to measure five power streams on a single phase.  With two systems like this, you could probably monitor every final circuit in the house.

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