This is a project I was going to patent in March last year, but the costs were horrendous and offered little protection against copying. So, although I have dismantled most of the working pro-types, I'm hoping this will qualify for the Invention Competition, and maybe encourage someone to perfect and possibly market the device.

A similar technique could be used to protect Mains 4 Way sockets or any environment where 'fuse popping' needs to be prevented.

I tried using cheap powerline communication with little success so I opted for 443 Mhz transmitters receivers.

iSwitch (An intelligent switch which is only enabled if maximum current will not be exceeded). ByT Reynolds March 2016 An inconvenience solved !

Touring caravan sites in the UK limit the amount of power which can be drawn from the electrical supply to 16 amps per caravan. In France, the limit is a mere 6 amps! A standard electric kettle draws about 9.5 amps which is fine providing not much else is running! When an electric grille is in use, switching on the kettle will pop the caravan trip. In some instances it may pop the supply post trip – these posts feed 4 caravans !

For some time now, energy monitors for the home have been available. Basically, the live or neutral feed to the distribution box is fed through a coil of wire and the output is measured by a micro controller and the voltage and current being drawn are displayed. My idea takes this a stage further! I have made an energy monitor with a touch screen display and a low power transmitter! The voltage and current are monitored in the same way as the commercial units. It is possible to set the maximum allowed current and an arbitrary warning level via the touch screen. (See circuit diagrams)

These two values are transmitted to all prepared sockets along with the mains voltage and amps being drawn. The power (Watts) is also calculated and displayed. A ‘channel code’ is also transmitted to prevent stray information from other devices nearby interfering with the receivers.

(See screen shots of the transmitter in set up & run mode).

Step 1: The Receivers

The receivers consist of a relay controlled mains socket, a display and a couple of switches. There is also a rotary encoder for the channel selection. I have made three types of receiver. A learning receiver, a fixed (known) value receiver and an RFID / NFC ad hoc receiver.

The learning receiver (Picture 1)

The learning receiver will ‘learn’ how much current a device is drawing. It will then store and display the information, along with the information sent by the transmitter. Armed with this information, the receiver socket is programmed to act as follows. If the stored amps value plus the amount of current which is being drawn is less than the Max value, the display will be green and the socket enabled. If this value is higher than the ‘warning’ level, the display is amber’. If this value is higher than the Max value, the display is red AND a relay in series with the live wire is opened. To prevent this relay opening and closing randomly when other devices are switched on and off, human intervention is required to close the relay and re-enable the socket.

The fixed value receiver Picture 2)

The fixed value receiver will work in the same way as the learning receiver. The two major differences are :- Its value will be pre-programmed, i.e. no learning facility so the current draw will be fixed The display will be replaced with red, yellow and green LEDs

RFID / NFC ad hoc (Pictures 3 & 4)

RFID / NFC ad hoc receiver power sockets will be fitted with a display showing the information as in version 1. The difference being, appliances and devices will be fitted with an RFID / NFC Tag which will hold information about the device i.e. what it is and how much current it draws. The display on the socket (which contains a reader), will display, for example, Hair dryer, Microwave, TV etc.and control the colour of the display and the relay when the device is plugged in. The relay will be open until the values have been read. In conclusion Because the electrical socket is ‘aware’ of how much current is being drawn at any given time, popping the trip could be avoided !

Step 2: Amendments, Conclusion & Hopes

I have modified a mains socket (on the RFID version) by adding a mechanical switch which is open when the plug is removed, this tells the Arduino that something has changed, so disable the relay until another is scanned.

I played around with a small magnet and a hall effect transistor to achieve the same, which worked fine, but I was not happy having to stick a magnet to a mains plug! Maybe, if ever the device goes into production, this could be manufactured into the plug and give a better option.

In my current system (excuse the pun), the mains sockets only receive information, using two way communication would be necessary for appliances with two power settings, eg a hair dryer in order to tell the other sockets (via the transmitter) that there is a possibility of a higher current draw (when the dryer is on the low setting) and send information accordingly.

My hope is that all future caravans would be fitted with an energy transmitting device as standard which could lead to other merchandising opportunities, i.e. RFID equipped appliances & devices.

The communication between the transmitter and receiver sockets could be I2C or RS485 instead of a low power transmitter which, although is an extra piece of wiring (network cable), it would simplify the sockets and eradicate the need for the 433MHz transmitters and receivers.