Controllers
As I now have 3 heat pumps I needed to design and build a control system for them.
After much brainstorming I decided to build a controller for each unit that is autonomous but connected to a central controller. This allows the individual unit to perform its own defrost if necessary. The main controller can send commands to the unit to switch them on and off and to force a defrost cycle if necessary (well why not!). Also each unit can be interrogated to report its status back to the main controller. Each unit has it's own address so can be individually controlled.
Each controller also has a manual override just in case! Also the units save their last operating mode (on or off) so will re-start in event of a power failure.
The control is implemented on an RS485 bus, this allows all the units to be connected to the same two wires and for each to listen for commands from the main controller. It also means the units will not conflict with each other when transmitting data as they are in a high impedance state when not actively transmitting.
I've built one of the controllers (pictures below before mounting in the machine) and am working on the main controller.
Acuario
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