The illustration shows the components mounted on a board before installation on the side wall of the airing cupboard.
To the top left is the HEMS itself (less cover) with 4 black output relays visible on the HAT of which two are connected via the white cables to operate car charger and immersion heater. Immersion heater software isn’t written yet but will mirror the charger software but on a second channel. Not illustrated is the power cable to the HEMS – a standard mobile telephone charger and USB cable.
To the top right is a 10-way junction box typically used for boiler installations. It takes switched inputs from the HEMS (x2) and ImmerSUN and uses them to drive the two outputs (radio transmitter and ImmerSUN Boost).
To the middle right is the existing radio transmitter used to operate the car charger. In this new installation it can be enabled either by the HEMS when the bought electricity price is low or by the ImmerSUN when our solar panels are in surplus.
To the bottom is the ImmerSUN. In addition to power in and power out to the immersion heater, there are also two control signals: (i) a relay contact that closes when solar is in surplus to drive the car charger and (ii) a relay input that can be configured as ‘Boost’ enabling full power to the immersion heater on an external signal (in my case from the HEMS).
Subsequently we not only have control of the immersion heater from the HEMS, but also have control of the mode of the storage battery switching between force charge, charge only and normal operation.