Review of inexpensive Chinese thermostat – STC-1000

This is a review of an inexpensive STC-1000 Chinese bang-bang  thermostat that was purchased on eBay for around A$12 complete with thermistor sensor and postage.

Above is the front view of the thermostat. There are many thermostats on the market with similar front panels, but they differ in internals and most importantly, performance and quality.

STC-1000-03

Above, the rating label is clear and informational, but it does not give the sensor parameters. 

STC-1000-02

Above, a view of the interior. To the lower left is a switched mode AC power supply to power the electronics. A risk with switched mode supplies is inadequate suppression of radio frequency emissions, and this one has radio frequency emissions in spades. There is no sign of RF filtering on the input or output of the power supply section, and emissions are high from the mains wires and sensor wires.

The sensor terminals are isolated from the mains terminals, but voltage withstand was not tested.

Observations

The calibration accuracy was checked with 10k and 2k0 0.1% resistors and the displayed temperature recorded, and calibration constants calculated (Two point thermistor calibration).

Screenshot - 11_07_16 , 14_43_39

The readings suggest a nominal 10k/3435 thermistor. Note that a two point calibration for a different temperature range is likely to yield slightly different results.

Quality

The thermostat is of poor quality due to its excessive radio emissions. It works well in other respects and there is adequate isolation between the primary power circuit, the sensor, and the output terminals.

This one is cheap Chinese junk.