Inside a ShangFang temperature controller

Video Description

Compared to the generic eBay units, this temperature controller is much better built and uses traditional power components and an external high current relay. The HVAC techs can judge will be the true reference if this type of module is reliable or not, as they may have come across them in use. The power supply is a traditional potted 2VA transformer, and the external relay means that when it does inevitably fail due to the number of switching cycles, it can be swapped easily without messing around with the controller and settings. The circuit design is traditional and very time-proven with good filtering on the thermistor input. This particular unit is a heating controller that could be used directly with resistive heating loads. It's notable that the PCB is a standard unit with the provision for two thermistors (plus circuitry for a third) and the capability of driving up to three external relays. It has provision on the module for a fourth button and a sounder. These are normally quite expensive, even on eBay, and I lucked out with a more affordable one being sold as a "refrigeration controller" when in fact it turned out to be a heating version. The display unit normally shows the measured temperature, but if the button is pressed briefly it flashes the set temperature and allows the user to adjust it within a range that has been determined by the installer. To program the unit the installer or service engineer holds the set button in for six seconds. When E1 is displayed the set button can be used to step through the options and the up/down buttons used to adjust them as follows. E1. The lowest temperature that can be set by the user. E2. The highest temperature that can be set by the user. E3. Hysteresis - the number of degrees from the set value that the unit activates. E4 Delay start - a time from zero to ten minutes that avoids frequent cycling of the load. E5 Thermistor calibration - allows the accuracy to be adjusted vs a calibrated thermometer. C1 Units of measurement - Celsius or Fahrenheit. If no button is pressed for ten seconds the unit stores the new settings and reverts back to its normal display. The hysteresis setting is to avoid rapid cycling of the load by adding a few degrees between on and off. If hysteresis is set to 3 degrees and the set temperature is 18 degrees then the unit will turn off the heater when it reaches 18 degrees, but not turn it back on until the temperature drops to 15 degrees. (18 minus the hysteresis value.) The delay start is a time setting to allow a load like a compressor to equalise pressure to reduce the risk of stalling if cycled off and on quickly, and also to reduce the stress on equipment caused by frequent starting. In the case of a heating unit like this one it may be set to zero. The COP mode may be a way to save the current settings as the new factory default ones to allow fast recovery after someone has tampered with them. Let me know if you've come across these in the wild, and how reliable they are. If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:- https://www.bigclive.com/coffee.htm This also keeps the channel independent of YouTube's algorithm quirks, allowing it to be a bit more dangerous and naughty. #ElectronicsCreators