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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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  • #31 17316264
    marycyś
    Level 12  
    Posts: 361
    Rate: 24
    I want to download from Aliex .. which has 8s003f3p6. But is it possible to change the software in it, is it not write-protected?
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  • #32 17316277
    miszczo997
    Level 28  
    Posts: 1052
    Help: 134
    Rate: 159
    Is not. To program, you need the programmer st link v2 and, for example, this batch from the link I gave above. If you want to write and compile the program yourself, you can use sdcc. You can find the appropriate header files for this processor on the web.
    A brief description of what and how here
  • #33 17316279
    TechEkspert
    Editor  
    Posts: 7047
    Help: 16
    Rate: 5457
    An interesting thing, if you manage to convert, I invite you to show the effects in DIY.
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  • #34 17316287
    marycyś
    Level 12  
    Posts: 361
    Rate: 24
    Is such a programmer from Aliex .. enough ?:
    1PCS ST LINK Stlink ST-Link V2 Mini STM8 STM32 Simulator Download Programmer Programming With Cover A41
  • #35 17316297
    miszczo997
    Level 28  
    Posts: 1052
    Help: 134
    Rate: 159
    Yes that's enough. To program it, you need to install stlink utility (drivers for the programmer will be installed) and stvp to upload the batch. I associate that it was somehow terribly unintuitive, but if you click, you will find which options to choose for the processor to program.
  • #36 17316347
    TechEkspert
    Editor  
    Posts: 7047
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    Rate: 5457
    What additional features do you want to get?
  • #37 17316402
    marycyś
    Level 12  
    Posts: 361
    Rate: 24
    I want to optimally manage the switching on of cooling, by additional analysis of switching periods, so as not to tire the aggregate (assuming additional tolerance).

    It's nice if you could use free pins, but I assume that there are no such pins anymore :)
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  • #38 17316415
    TechEkspert
    Editor  
    Posts: 7047
    Help: 16
    Rate: 5457
    The use of a ready-made board will speed up the implementation of the device, but it may turn out that such missing pins you write about or other difficulties may direct the project to make it from scratch, i.e. designing both the layout and writing the code.

    What do you mean by additional analysis of switching periods, something like PID, or more conditions for optimizing the number and intervals of actuator switching. Are the options available in this controller (e.g. hysteresis) not sufficient for cost-effective control?

    On / off control is generally not very optimal in many respects (for example the example of the temperature graph in the first post), but in many cases it is sufficient and, importantly, simple to implement. An example is an on / off and inverter air conditioner (there are both advantages and disadvantages of both solutions).
  • #39 17474858
    piterek-23
    Level 33  
    Posts: 3321
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    Rate: 426
    Is the "probe" waterproof / waterproof?
    I would like to use this module for an aquarium heater ;)
  • #40 17475289
    nici
    VIP Meritorious for electroda.pl  
    Posts: 4961
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    Rate: 977
    piterek-23 wrote:
    Is the "probe" waterproof / waterproof?
    Yes.
  • #41 17475437
    piterek-23
    Level 33  
    Posts: 3321
    Help: 162
    Rate: 426
    nici wrote:
    piterek-23 wrote:
    Is the "probe" waterproof / waterproof?
    Yes.

    Thanks.
    I opened the manual, and there Temperature sensor type: NTC (10K 0.5%) waterproof ;)
    I ordered the thermostat in our shop, we will see how it will work in the aquarium ;)
  • #42 17475824
    TechEkspert
    Editor  
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    If it was to be constantly immersed in water, I would prefer to somehow additionally secure it with, for example, a heat shrink tube (unfortunately there will be additional thermal insulation ...), or some varnish?
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  • #43 17475828
    pierotez
    Level 14  
    Posts: 472
    Help: 2
    Rate: 85
    One note about this detector. On aquarium forums they reported after about half a year that the measurement started to go crazy. It turned out that the probe was corroded and gave other false results! There is a method for this, when I cover the probe with a heat-shrink and taped it on both sides and it's completely OK.
  • #44 17475842
    piterek-23
    Level 33  
    Posts: 3321
    Help: 162
    Rate: 426
    It was supposed to be so beautiful...
    Thanks, gentlemen, for the idea of a heat shrink T-shirt ;)
  • #45 17475853
    TechEkspert
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    A long time ago, when I had an aquarium, I used a temperature controller with a thermistor and an operational amplifier controlling the relay to which the heater was connected. I placed the thermistor in a small dough aroma vial which was filled with sand and topped with paraffin and glue. Such a sensor worked flawlessly for many years. I was concerned about some great thermal inertia, but compared to the mass of water, it didn't really matter ...
  • #46 17475986
    piterek-23
    Level 33  
    Posts: 3321
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    Rate: 426
    Yes, I look at the photos, the NTC sensor is flooded in a metal housing, so why is it rotting?
    The weak glue (what's in there) lets the water through, or does the metal core rot?
  • #47 17477183
    pierotez
    Level 14  
    Posts: 472
    Help: 2
    Rate: 85
    The metal rots / bleds and gives a dozen%, but I don't remember which way.
    After heat-shrink or other means, the problem disappears, checked!
    Only I used a 2-ingredient, not a thermoglute.
    Simple bag, nothing to be afraid of and the probe would be replaced by the bank in six months ;)
  • #48 17477192
    vodiczka
    Level 43  
    Posts: 30170
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    pierotez wrote:
    Only I used a 2-ingredient, not a thermoglute.
    With two-component, it is enough to apply a layer of adhesive 2-3 times over the entire surface of the probe.
  • #49 17477336
    pierotez
    Level 14  
    Posts: 472
    Help: 2
    Rate: 85
    I did not think about it. The T-shirt is easy and simple to make ;)
  • #50 17983633
    sergiuszf
    Level 12  
    Posts: 87
    Rate: 160
    Good day.
    I bought such a thermostat and during its conversion to control up to 999 degrees, everything worked fine until something suddenly happened.
    Namely, all 3 letters "LLL" jumped out suddenly during the work, means the limit of lower temperature was exceeded.
    But in fact nothing was surpassed, I rummaged through all the settings and nothing. When turned on, 3 "LLL" lights up immediately, which means it does not show the temperature, although the whole settings menu is working, and it should be.
    I tried to reset the controller at all by turning it on with initial simultaneous pressing of the "+" and "-" buttons. Nothing again. 3 "LLL" are displayed
    What could it be?
    Please help.
  • #51 17983657
    Rezystor240
    Level 42  
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    sergiuszf wrote:
    What could it be?


    The probe just disconnected, maybe the wire has rubbed in some place?
  • #52 18022978
    sergiuszf
    Level 12  
    Posts: 87
    Rate: 160
    I've finally explained what the matter is. It turned out that the microcontroller has broken, the 6th leg of the controller that processes the signal sits on the ground. And, oddly enough, in the chip itself. I crossed the paths all the way to the chip, and it turned out that the 6th leg has a short circuit with the ground.
    It's very strange that everything else works, so all functions work except measuring the input signal.
  • #53 18210292
    dgproject
    Level 13  
    Posts: 183
    Rate: 272
    I'll include my few pennies.
    For me, I used these modules to heat the DHW tank through an additional SSR 10A relay and I must admit that it flashes as it should.
    In addition, I built a simple fireplace blower controller from 3 pieces.
    The modules manage the blowing force of a four-speed fan with a maximum power of 400W depending on the degree of heating (I only use 3 gears)
    For this purpose, I had to solder additional wires to the relays due to the lack of NO / NC on the PCB.
    Overall a very useful device.
  • #54 19059259
    draglukasz
    Level 12  
    Posts: 131
    Rate: 20
    I have a problem with this thermostat, because the temperature values are constantly fluctuating, with a constant temperature it shows changing temperature values every few seconds, eg 13.0; 13.7; 12.6, 13.1 etc.
    I changed the probes, nothing worked.
  • #55 19059478
    dgproject
    Level 13  
    Posts: 183
    Rate: 272
    Such their accuracy ...
    Unfortunately, the sensors used in these systems are not the same as PT100, which is a pity.
    For basic applications where there is no need to use high resolution measurements, they are rather suitable.
    For precision applications, I recommend PID controllers for PT100 and a solid-state SSR relay.
    Costs several times higher, but:
    Pros:
    + high measuring accuracy
    + Larger temperature ranges
    + More setting options
    + no moving parts (relays)
    + Alarm output
    And a lot more...
  • #56 20846901
    Fisqss
    Level 6  
    Posts: 13
    Rate: 10
    Hello,

    Let me start by saying that I am an amateur :)

    I bought the W1209 thermostat mentioned here, but the temperature sensor that I have to use has three wires (red, yellow, black). How can I connect it so that it works and shows the correct temperature since the thermostat has two wires? when I connect only 2 wires, it shows the temperature more than 3 times higher than the actual temperature.

    Thank you in advance for your help

    Regards
  • #57 20847154
    vodiczka
    Level 43  
    Posts: 30170
    Help: 1183
    Rate: 4287
    Fisqss wrote:
    I bought the W1209 thermostat mentioned here, but the temperature sensor that I have to use is 3-wire

    This thermostat has its own sensor, using another one (with different parameters) will give false measurement results.
    Write exactly what sensor you have.
  • #58 20847307
    Fisqss
    Level 6  
    Posts: 13
    Rate: 10
    Thank you for your answer. I have such a sensor "Waterproof temperature sensor DS18B20"
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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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