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W1209 thermostat, test, opinion, applications

TechEkspert 20190 61

TL;DR

  • The W1209 thermostat controls heating or cooling loads with an NTC sensor, 0.1C display resolution, a simple SET/+/- menu, and an included plexiglass housing.
  • Its P0–P6 settings select heater or cooler mode, set 0.1–15C hysteresis, calibrate the probe, add relay delay, and trigger an emergency alarm shutdown.
  • It runs from 12V, draws about 16mA with the relay off and 65mA when the relay is energized, and its relay is rated for 20A at 14VDC.
  • A test with a 4.7 ohm resistor at 45C showed visible on/off cycling and delayed temperature response from thermal inertia.
  • The setup works well for simple thermostatic control, but tighter regulation would need PWM, phase control, or a PID controller.
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  • W1209 thermostat, test, opinion, applications
    The W1209 thermostat can control a heating or cooling device. The LED display shows the current temperature with a resolution of 0.1C, measured with a sensor based on the NTC element. The simple menu of the system allows, among others, to define the type of controlled device, calibrate the thermometer readings, and determine the hysteresis range. The system is supplied with 12V and consumes ~ 16mA with the relay turned off, while the relay coil is powered, the current consumption increases to 65mA. Relay contacts, as described, can switch 20A at 14VDC and 20A at 125VAC. A plexiglass housing is included with the thermostat.

    The W1209 thermostat will soon appear in the elektroda.pl gadgets.

    To set the set temperature, shortly press the microswitch marked SET (the digits on the display will start blinking) and use the + - buttons to set the temperature to be stabilized by the thermostat. We can set the value from -50C to 110C.

    Holding the SET button for longer than 5s displays the menu items from P0 to P6. Entering the settings of a certain menu level is done by pressing the SET button.

    P0 - select the type of connected device:
    H- a device generating heat, i.e. a heater, e.g. in the form of a resistor
    C- cooling device, e.g. fan or Peltier module, C is the default setting

    P1 - we set the hysteresis, i.e. the deliberate interval between switching on and switching off an element, by default they are 2C (0.1-15 adjustment),
    e.g. in case of cooling and the thermostat temperature is set to 20C, cooling will be turned on after reaching 20C,
    while cooling will be turned off at 18C (2C hysteresis). Setting the hysteresis will reduce the number of switchings of the relay, increasing the life of the contacts.

    P2 and P3 - setting the maximum and minimum temperature (by default set to the maximum and minimum measurement, I do not know what is the practical application)

    P4 - temperature sensor calibration -7C to 7C. A one-point calibration is debatable, but for the thermostat's setpoint temperature it may make sense.

    P5 - delay time of switching on the relay.

    P6 - extreme temperature alarm, when the temperature reading reaches the set alarm threshold, the relay will be turned off, the symbol --- will appear on the display. You can set this value to a temperature that is dangerous for the system, in an emergency the heater power supply will be turned off.

    The NTC sensor is closed in a metal housing which increases its resistance to damage. When the sensor is disconnected, the thermostat displays LLL. Room temperature readings are the same as with a thermocouple multimeter.
    W1209 thermostat, test, opinion, applications

    Connecting the controlled receiver is very simple. The relay is connected in series in the receiver power supply circuit. We supply 12V DC to the thermostat.
    W1209 thermostat, test, opinion, applications

    Let's make a test and use a 4.7om resistor powered from 12V as a heating element. Place the sensor so that it measures the heater temperature. At the same time, we can record the temperature of the resistor.
    W1209 thermostat, test, opinion, applications
    We set the thermostat to 45C and see how the on / off control is doing.
    W1209 thermostat, test, opinion, applications

    Considerable temperature fluctuations caused by the "inertia" of the system are visible. Around 45C you can see the moments of switching on the relay, but despite switching off the power supply to the resistor, the temperature rises for some time, then the temperature drops until the relay is switched on again. This example shows that the accuracy of the temperature sensor and measurement may not be of great importance in on / off control. Such simple control will prove itself in many applications. In more demanding applications, the heater can be controlled, for example, by PWM or phase, and even a PID controller as a controller.

    In the set with the W1209 thermostat you will find a plexiglass housing.
    W1209 thermostat, test, opinion, applications

    Where do you see the applications for the W1209 thermostat?
    W1209 thermostat, test, opinion, applications

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    TechEkspert
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  • #2 17177772
    ElectroTom
    Level 25  
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    And how to measure negative temperatures, e.g. -10 degrees Celsius or - 20.
  • #3 17178161
    Niebieski
    Level 12  
    Posts: 55
    Rate: 2
    For me, the third season controls the central heating pump.
  • #4 17178555
    miszczo997
    Level 28  
    Posts: 1052
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    How are minus temperatures indicated? Somehow I was recently looking for an alternative to a mechanical freezer thermostat because I couldn't find a suitable one for my medel and was considering buying a stc1000 ($ 10) regulator. I rejected the W1209 right away, because after the Chinese descriptions I concluded that it can only control the heating elements. If I had known then that it can also cool, I would have used it for sure. Especially that with the old thermostat there was a lot of space and I would have put some power supply there.

    Added after 4 [minutes]:

    It is a pity that there is no buzzer, because it would work perfectly with options P2, P3 and P6. The control microcontroller is some stm8? Maybe there are some software sources.
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  • #5 17179031
    TechEkspert
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    @ElectroTom @ miszczo997 negative temperatures are indicated by a minus,
    with two-digit numbers the resolution of indications is reduced:
    W1209 thermostat, test, opinion, applications W1209 thermostat, test, opinion, applications

    The control system is a Chinese nouvoton N76E003AT20 enriched 8051.

    @Blue* i.e. a durable product, it starts the circulation pump when the water temperature rises and stops when it drops?
  • #6 17179134
    Granat :)
    Level 34  
    Posts: 3043
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    The biggest disadvantage of this thermostat in my opinion is that when the maximum temperature (I don't know how the minimum) is reached in cooling mode, the relay is turned off.
    Let's assume that the cooling does not work and the sensor reaches 110 ° C, but the relay should not turn off the actuator, i.e. cooling, because the temperature will increase even more.
  • #7 17180033
    krisRaba
    Level 31  
    Posts: 1999
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    Granat :) wrote:
    The biggest disadvantage of this thermostat in my opinion is that when the maximum temperature (I don't know how the minimum) is reached in cooling mode, the relay is turned off.
    Let's assume that the cooling does not work and the sensor reaches 110 ° C, but the relay should not turn off the actuator, i.e. cooling, because the temperature will increase even more.

    This may be a deliberate safeguard, i.e. the controller switches the actuator on, but sees no changes in the feedback signal. It may be a situation that you write about, e.g. cooling does not work, but there may also be a lack / damage of the sensor (although it is supposed to be missing by LLL) - then switching on the actuator (heater, compressor, air conditioner) may be an error and continuous operation can damage them if they are not adapted to it (and not all are). Overall, the description of P6 suggests intentional action. The question is, do you have to set P6 or not?
    In fact, knowing what you are controlling, i.e. whether continuous work can cause damage or not, behavior in this situation should be configurable.
    On the other hand, this is a very extreme case when you are cooling and maybe quite the case when you are outside the thermostat's operating range. I understand that you are not able to cool something down to the set 25 degrees Celsius, because due to e.g. high sun exposure, the air conditioner or other devices with poor performance swing e.g. around 40 degrees ... Then it should actually cool 100% of the time, despite not reaching the set temperature. But a complete lack of response to the operation of the thermostat and going beyond the operating range is rather a mistake.
    On the other hand, for "critical missions" something like this is unlikely to apply ;)

    Well, one more question .. because it may be the opposite (unless you state it on the basis of usage, not just the description from the first post). Ie. you set the maximum temperature in heating mode, if for some reason the regulator would like to exceed a temperature that is dangerous for the system, it turns off and, similarly for cooling, you set the minimum - you chilled too much, squeak, off ;)
  • #8 17180084
    AndyNW
    Level 12  
    Posts: 30
    Rate: 3
    Hello, I control the CO circulating pump in the furnace. OK.
  • #9 17180483
    nici
    VIP Meritorious for electroda.pl  
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    Granat :) wrote:
    The biggest disadvantage of this thermostat in my opinion is that when the maximum temperature (I don't know how the minimum) is reached in cooling mode, the relay is turned off.
    Let's assume that the cooling does not work and the sensor reaches 110 ° C, but the relay should not turn off the actuator, i.e. cooling, because the temperature will increase even more.


    You do not need to use this feature, it can actually be troublesome in some situations.
  • #10 17181491
    TechEkspert
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    @krisRaba P6 can be set to OFF.
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  • #11 17181913
    krisRaba
    Level 31  
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    And after the "biggest flaw" ;)
  • #12 17183039
    cocokoko
    Level 11  
    Posts: 7
    Rate: 2
    I have been using two such thermostats for two years. One controls the hot water circulation pump, the other controls the relay that activates the electric heater when the water temperature in the boiler drops below the set value.
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  • #13 17185602
    dgproject
    Level 13  
    Posts: 183
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    I use three such modules to control the airflow power in the DGP installation in the fireplace and they do well with the appropriate setting of parameters.
    The only drawback, in my opinion, is the lack of a full transmission Inka connector, which forced me to solder at the bottom of the PCB ;) W1209 thermostat, test, opinion, applications
  • #14 17187842
    vodiczka
    Level 43  
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    TechEkspert wrote:
    Room temperature readings are the same as with a thermocouple multimeter.
    I read on the electrode forum that while the indications in the range of 10-30 ° C are correct with an accuracy of 1 ° C, as the temperature increases, they are burdened with more and more errors.
    When I receive the ordered copy, I will check and report the results in a wider temperature range.
  • #15 17188222
    Rezystor240
    Level 42  
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    an interesting thing about this thermostat.
    For me, it would be used with a laminate etching machine.
    I can never sense the matter and sometimes I can boil acid.
    This thermostat fits perfectly, if the limit is over and it will still be in the store, I take it.
  • #16 17189979
    brofran
    Level 41  
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    I believe that the range of voltage of the executive relay contacts (24 and 125 V) is a big disadvantage. After all, the typical voltage of our home installations is 240 V AC. :cry:
  • #17 17190393
    vodiczka
    Level 43  
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    brofran wrote:
    After all, the typical voltage of our home installations is 240 V AC.
    It will withstand 125V, it (judging from previous posts) will also withstand 240V at a much lower current, and at 20A I do not believe it, despite the manufacturer's assurances.
  • #18 17191858
    Granat :)
    Level 34  
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    P6 does not work on off, only a range is set. I have it set to max, ie 110. The sensor is on the boiler flue, at a distance from it, otherwise it would be 300 ° C. Rarely, because rarely, but if you want to, you can light it up so that the temperature rises. The thermostat controls the buffer charging pump.
    But these are only temporary, I've already figured out a better way .. and a new boiler ;)
  • #19 17198520
    AndyNW
    Level 12  
    Posts: 30
    Rate: 3
    Hello, I apply to CO in a single-family home. It works fine
  • #20 17206537
    Niebieski
    Level 12  
    Posts: 55
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    TechEkspert wrote:
    @Blue*, which is a durable product, starts the circulation pump when the water temperature rises and stops when it drops?


    I have a single-function boiler and a heat exchanger. The thermostat controls the pump in the radiator circuit. It turns it on when hot water from the boiler appears and turns it off when it cools down in the pipe.
  • #21 17207502
    vodiczka
    Level 43  
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    TechEkspert wrote:
    P4 - temperature sensor calibration -7C to 7C. A one-point calibration is debatable, but for the thermostat's setpoint temperature it may make sense.
    How to understand? Is it so that after setting the selected temperature I can compensate the difference between the actual and the measured temperature and displayed at the time of switching the thermostat, as long as the difference between them is not greater than +/- 7 ° C.
  • #22 17208700
    TechEkspert
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    This should be understood as a single point calibration,
    the thermostat shows us 20.5C, and the exact thermometer 20C,
    we correct the indication so that the thermostat at this point shows 20C,
    as I wrote in this system, such calibration is debatable.
  • #23 17210026
    vodiczka
    Level 43  
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    TechEkspert wrote:
    as I wrote in this system, such calibration is debatable.
    If we assume that it is not a sensor calibration but a compensation or correction of indications, this is a helpful solution. Unfortunately, I just received the thermostat today and it is pale. In the negative temperature range -24 ° C to -30 ° C (indications of the DT 9908A meter), the thermostat shows the temperature by approx. 10 ° C higher, i.e. the difference in indications is greater than the possible correction range.
    After introducing the maximum correction, i.e. -7 ° C, the difference decreased to three degrees, e.g. the meter showed -28 ° C and the thermostat -25 ° C

    Added after 1 [hours] 11 [minutes]:

    The thermostat is factory set to the cooling function (C), the activation temperature + 28 ° C and the hysteresis of 2 ° C. In the temperature range of + 18 ° C to + 50 ° C it is better. After introducing the -5 ° C correction, the differences in the meter and thermostat indications in the above-mentioned temperature range do not exceed 1.5 ° C
    The introduced correction is saved in the memory and does not need to be re-entered after switching it on again.
  • #24 17210353
    Freddy
    Level 43  
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    @TechEkspert Correct the description a bit:
    Quote:

    P0 - type of work H-heater / C-Cooler cooling
    P1 - hysteresis (0.1 ° C ... 15 ° C, default 2 ° C).
    P2 - upper operating temperature limit from -45 to 110 ° C ... (default 110 ° C).
    P3 - lower operating temperature limit -50 ° C ... 105 ° C (-50 ° C by default) - P2 and P3 allow to narrow the temperature range for safety reasons (limits of possible activation temperature settings)
    P4 - temperature correction (-7 ° C ... + 7 ° C, the default value is 0 ° C) - Allows a simple calibration to improve the accuracy of the measurement (only characteristic shift);
    P5 - relay operation delay (0-10 s, default 0) - It is sometimes necessary to delay the refrigerator compressor;
    P6 - alarm for too high signal temperature (0 + 110 ° C, disabled by default).

  • #25 17265473
    Justyniunia
    Level 36  
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    I want to build a lawn mower based on this thermostat, but ...

    # 1. How to measure the temperature of B327? Because probably not directly?
    Do you have a patent for shielding the sensor from acid, or maybe you don't have to?

    # 2. Is the use of power resistors as heating elements a good idea?
    You could use a 12V power supply and this factory 14V / 20A relay.
    In total, the temperature maintained at 40 * C does not require a heater with a power of hundreds of watts.

    PS:

    Horizontal lawn mower in the form of a cuvette (a cuvette from an old kitchen scale), rocking with a motor with a gear.
  • #26 17265599
    vodiczka
    Level 43  
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    Justyniunia wrote:
    Do you have a patent for shielding the sensor from acid, or maybe you don't have to?
    I wouldn't risk without cover.
    The easiest way to apply a protective layer is to dip it in the varnish 2-3 times. Unfortunately, I will not tell you what.
    Does your thermostat require a temperature correction when measuring room temperature? If so, how big?
  • #27 17266757
    Justyniunia
    Level 36  
    Posts: 4188
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    At the melting point of the ice the thermostat showed 1.9 ° C, it was calibrated down by these 1.9.
    Now it shows 0 * C
    Under the tongue I have 36.5 * C, which would be correct.
    In the room, alcohol shows 24.5 dashes, thermostat 24.4 * C
    I still have to check the boiling water, but I think now everything is OK after calibration.
  • #28 17308308
    marycyś
    Level 12  
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    Is it possible to change the software of this driver?
  • #29 17316230
    TechEkspert
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    Theoretically, everything can be done if the microcontroller allows for re-programming. However, in this case, you would have to write the software from scratch, as well as draw the driver diagram and use the appropriate compiler for the microcontroller.
    This version is based on the N76E003AT20 (Chinese enriched 8051), I've also seen similar copies with some ST.
  • #30 17316242
    miszczo997
    Level 28  
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    For those done on stm there are modified software among others this https://github.com/TG9541/W1209
    also saw some specials for brewers.
    For the N76E003AT20 I did not find anything, probably because to program it you need quite an expensive programmer.
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Topic summary

✨ The W1209 thermostat is a versatile device capable of controlling both heating and cooling systems, featuring an LED display with a temperature resolution of 0.1°C. Users have discussed its applications, including controlling central heating pumps, electric heaters, and circulation pumps in various setups. The thermostat operates on a 12V supply and has a relay capable of switching 20A at both 14VDC and 125VAC. Concerns were raised about its accuracy at extreme temperatures, particularly in the negative range, and the lack of a buzzer for alerts. Users have also noted the importance of calibrating the device and the potential for software modifications. The NTC temperature sensor is waterproof, but users have reported issues with corrosion over time. Overall, while the W1209 is praised for its functionality, reliability issues with the relay and sensor longevity have been highlighted.
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FAQ

TL;DR: Relay handles 20 A @ 14 VDC [Elektroda, TechEkspert, post #17177090]; "works fine" when driving a CO pump [Elektroda, AndyNW, post #17198520] Fans love the W1209 for its −50 °C…+110 °C span and ₹300-level price. Why it matters: cheap, hackable control beats mechanical thermostats.

Quick Facts

• Temp span: −50 °C to +110 °C, 0.1 °C step [Elektroda, TechEkspert, post #17177090] • Hysteresis adjustable 0.1–15 °C via P1 [Elektroda, TechEkspert, post #17177090] • Supply: 12 V DC, 16 mA idle / 65 mA relay on [Elektroda, TechEkspert, post #17177090] • Relay contacts: 20 A @ 14 VDC or 20 A @ 125 VAC (expect ≈5 A @ 240 VAC) [Elektroda, TechEkspert, #17177090; Elektroda, vodiczka, #17190393] • Board MCU: N76E003AT20 or STM8S003F3P6, both re-flashable [Elektroda, TechEkspert, #17179031; miszczo997, #17316242]

1. What temperature range can the W1209 measure and control?

The on-board firmware accepts set-points from −50 °C to +110 °C. The same limits apply to displayed readings and to the P2 (upper) and P3 (lower) safety boundaries [Elektroda, TechEkspert, post #17177090]

3. Is the supplied NTC probe waterproof?

Yes, the NTC is potted in a metal sleeve, but corrosion in aquaria has been reported after 6 months. Slide on heat-shrink or coat with two-part epoxy to seal it fully [Elektroda, pierotez, post #17475828]

4. Can the relay safely switch 230 V AC mains loads?

The PCB relay is rated 20 A @ 125 VAC; users confirm it survives 240 V AC but at lower current (~5 A) [Elektroda, vodiczka, post #17190393] For higher power, drive an external contactor or SSR instead.

6. What do parameters P0–P6 actually change?

P0: Heat (H) or Cool (C) P1: Hysteresis 0.1–15 °C P2/P3: Max/Min set-point limits P4: Sensor offset −7…+7 °C P5: Relay delay 0–10 s P6: Over-temp alarm OFF or 0…110 °C [Elektroda, Freddy, post #17210353]

7. How do I disable the P6 alarm that kills cooling at 110 °C?

Enter menu (hold SET 5 s), scroll to P6, set value to OFF. The relay then ignores the temperature ceiling [Elektroda, TechEkspert, post #17181491]

8. Can I replace the probe with a 3-wire DS18B20 sensor?

No. The firmware expects a 10 kΩ NTC. A DS18B20 will read 3× too high even with two wires connected [Elektroda, Fisqss, #20846901; #20847307]. Swap in any waterproof 10 kΩ NTC instead [Elektroda, vodiczka, post #20847443]

9. How reliable is the board?

Field data: about 20 % of new boards have relay contact issues and occasional MCU failure has been logged (pin 6 shorted) [Elektroda, Kkaz, #21156208; sergiuszf, #18022978]. Quote: "very unreliable thermostat" [Elektroda, Kkaz, post #21156208]

11. How do I quickly set a target temperature with hysteresis?

  1. Tap SET; digits blink. 2. Use +/− to choose target, tap SET to save. 3. Hold SET 5 s, pick P1, set hysteresis, save. The relay now toggles at target±hysteresis/2 [Elektroda, TechEkspert, post #17177090]

12. What are common applications shared by users?

Users drive CO pumps, DHW heaters, fireplace blowers, aquarium heaters, PCB etching baths, and lawn-mower acid batteries [Elektroda, multiple posts #17178161, #17183039, #18210292, #17265473]. A 65 mA coil current lets battery systems run efficiently [Elektroda, TechEkspert, post #17177090]
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