This article documents the build of a DIY thermostat based on an inexpensive ($12) Chinese temperature controller.
The controller used is a 220VAC MH1230A.
Above is an internal view of the controller. Importantly it has a relay rated at 240V 30A, and 15A at PF=0.4. The datasheet rates the relay for a 2HP (1.5kW) motor. It uses a ‘conventional’ power supply, the brown component is the power transformer. Most similar products use inadequate relays and have low grade switched mode power supplies that create RF noise.
For all that it has a 30A relay, the tracks and screw terminals are not suited to more than 10A.
Beware when buying these, the Chinese cheats substitute product, and label different controllers to suit the buying demand of the times… take the cover off and inspect.
The box cutouts were done on a CNC router, but they could be done with hand tools.
Above, calcs of feeds and speeds for the CNC router. The box is actually ABS, but cutting speed for Polycarbonate is the same.
Above is the tool path for one side of the box. The cutouts suit the 7P-2 strain reliefs and the SP13 connector. The gcode is generated from a custom Python file using a custom library of common shapes that I use.
Above, the box cutouts were done on a CNC router.
- MH1230A 220V controller;
- extension cord;
- 2x Heyco 7P-2 strain relief bushings;
- SP13 2 pin plug and flange mount socket + 2x M3x10 screws and nuts;
- 2x bootlace terminals and one end splice for ground; and
- self adhesive rubber feet.
Warning: I would not use the low grade Chinese closed end terminal that use a soft aluminium sleeve for a ground / protective earth connection.
You will need to strip sufficient cable to be able to wire the controller before inserting it through the aperture as the terminal screws will not be accessible when the module is fitted to the box (well, unless you build it upside down). Install the strain reliefs so that the module can be remove without removing the strain reliefs.
Above, controller wired and ready to be turned over and inserted in the box.
Above, the completed thermostat.
Do not undertake this project unless you have the necessary competencies.