Help putting together electricity monitoring/billing system

hi, i'd appreciate some help with the following:

the background

i have a very basic understanding of household electrical installations. i am a part owner of a small boarding house with 13 bedrooms. the house has a main 3 phase distribution board. there are an additional 2 more sub-distribution boards. one in one room, feeding that room and another feeding 4 rooms. the wiring is not straight forward as for example, one plug wire may run from the main board, enter a room, feed 3 wall plugs then go through a wall to feed a plug in another room. this second room may have an additional 3 plugs which may be fed from another wire coming through another wall from another room. etc (the house has undergone many renovations over the years with additions, etc). the separate lighting wires are similarly mixed up. it's a 220 volt system (south africa)

my requirements

i would like to install some system so that each room occupant is responsible for their own electricity costs. either with a prepaid system in each room or a central PC with a database of all individual costs (sent to the PC from suitable sensors) so that the occupant could be billed accordingly.

guidance needed

so, i'd appreciate any help to achieve my goal. maybe someone could give some suggestions on what to do, maybe point me in the direction of helpful websites, forums, etc. or maybe there are some off-the shelf products that could be used as is or maybe tweaked a bit?

thanks in advance


calypso_rae's picture

Re: Help putting together electricity monitoring/billing system

Hi Clive,

I think the first thing you'll require is a clear understanding of how the mains power flows within the premises.  Having drawn up a sufficiently detailed diagram, you will then be able to identify the particular locations where the flow of power needs to be measured.  An emonTx at each of these locations could then continuously transmit power data to a central point where the relevant stats can be calculated.

For example, person X may be responsible for the power seen at point Y minus that seen at point Z.  This is the same principle as on the solar PV monitoring page where consumed power is calculated using the equation:

Power consumption = Solar PV generation + Grid import/export (negative when export)

For accurate charging data, it would seem best for power to be monitored continuously rather than only every few seconds.  I'm not sure whether any of the standard OEM sketches will do this but there are several people on the forum who should be able to help.

The project sounds entirely do-able to me.


Robert Wall's picture

Re: Help putting together electricity monitoring/billing system

I agree that it should be do-able, but in practice I feel it is likely to be full of difficulties. You've written that there are 13 potential customers, each has a lighting and a power supply. That immediately suggests a minimum of 26 monitoring nodes. Then you have the problem of accuracy: where one 'customer' is supplying the second, it is quite important that the readings are accurate. I see a potential for disputes there.

I go along with Calypso_rae's suggestion of generating an accurate diagram of the wiring, you can do nothing without that. When you have it, the scale of the problem will be clear and you can set about costing it. At that point, it would be a good idea to get quotes for a complete rewire with a "master" 13-way distribution board and 13 satellite boards. I'm fairly sure that would be a lot more expensive, but it would be good to have the information.

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