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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#61 20847443 05 Dec 2023 12:10

vodiczka vodiczka

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Post #61
20847443 05 Dec 2023 12:10

It should work, the original NTC sensor also has a resistance of 10 kΩ
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#62 21156208 16 Jul 2024 08:06

Kkaz Kkaz

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Post #62
21156208 16 Jul 2024 08:06

I have been using the W1209 for several years, and can share models for a DIN rail 3D printer and a wall switch. Functionally great. Unfortunately, in practice it is a very unreliable thermostat: about 1 in 5 new ones has a relay that contacts correctly, so you have to check with an ohmmeter right away and send back the faulty ones. Scalak fries without giving a ration, etc. I haven't had a sensor die yet, but in other units these 10k NTCs drop like flies once a year, so I'd install a few at once in units that are then hard to get to. The indications from the sensor are generally insensitive to cable extension.
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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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W1209 thermostat, test, opinion, applications

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]

2. How are negative temperatures displayed?

The display shows a leading minus sign; resolution drops to 1 °C for two-digit negatives (e.g., −18, −19) [Elektroda, TechEkspert, post #17179031]

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.

5. How accurate is the thermometer and how do I calibrate it?

Uncorrected error is typically ±1 °C from 10–30 °C, worsening beyond 30 °C [Elektroda, vodiczka, post #17187842] Use P4 to add −7 °C…+7 °C offset: 1) Measure with a reference, 2) Hold SET 5 s, pick P4, 3) Adjust until readings match [Elektroda, TechEkspert, post #17208700]

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]

10. Can I re-flash the firmware?

Yes. STM8 versions program via ST-Link V2 and open-source builds like TG9541/W1209 [Elektroda, miszczo997, post #17316277] N76E003 versions need a Nu-Link programmer and full rewrite [Elektroda, TechEkspert, post #17316230]

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

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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