Elektroda.com
Elektroda.com
X
Elektroda.com

Tuya Smart High Power Switch for Boiler Water Heater

yarix2 1566 12
  • Hello,
    In this post, I will share teardown of Tuya Smart switch for boiler water heater and flashing it with OpenBK7231N.
    Tuya Smart High Power Switch for Boiler Water Heater Tuya Smart High Power Switch for Boiler Water Heater Tuya Smart High Power Switch for Boiler Water Heater Tuya Smart High Power Switch for Boiler Water Heater

    The switch was bought on Aliexpress, the major reason to buy this device is it’s advertised high power, 20A 4400W !! (I have very bad experience with cheap Sonoff 16A switches that nearly burned my entire house after few weeks of operation).
    after discovering this forum... i had to give Tuya a try ;)

    I was really hoping to get an old device with either ESP chip or at least WB2S, however the switch came with CB3S and BK2731N, which made the process a bit more educational (aka complicated).

    Teardown:
    Tuya Smart High Power Switch for Boiler Water Heater
    Tuya Smart High Power Switch for Boiler Water Heater

    The front glass cover is easily removed, and the 1st PCB layer with the LED and CB3S module are exposed.
    This PCB is connected with 4 pins socket to a 2nd PCB which contains the relay and power circuit. In between there is a thin film layer (like in other switches from Tuya).
    For the firmware upgrade there is no need to disassemble the 2nd PCB. Just remove the 1st PCB from its housing.



    CB3S:
    for the firmware upgrade we need to work with the following pins, (complete table is here)
    Tuya Smart High Power Switch for Boiler Water Heater







    PINDescription
    1RESETneed to short to ground for ~1sec. when flashing begins.
    8VCC-3.3VDC 3.3v
    9GNDGround (DC -)
    15RXD1UART1_RXD (user serial interface), which corresponds to P10 of the IC.
    16TXD1UART1_TXD (user serial interface), which corresponds to P11 of the IC.


    Prepare to flash on windows:
    1. install python3 (i used 3.7)
    2. get hidapi from https://github.com/libusb/hidapi/releases, extract it to somewhere in windows %PATH%
    3. git clone hid_download_py repo
    4. create virtual env, and activate it.
    Code:

    C:\repoo\hid_download_py>python -m venv c:\repoo\hid_download_py\py37-3nv
    C:\repoo\hid_download_py>py37-env\Scripts\activate

    5. run install
    6. test installation
    Tuya Smart High Power Switch for Boiler Water Heater
    7. Download the latest bin firmware file from https://github.com/openshwprojects/OpenBK7231T_App/releases, I used OpenBK7231N_QIO_1.12.44.bin

    Prepare to flash hardware:
    1. Breadboard with few cables
    2. A 3.3v power supply
    3. USB to serial adapter FT232RL FTDI
    4. FIMO clay or soldering iron...

    To avoid soldering, I’ve used some FIMO clay to hold breadboard cable pins right on the chip. This method requires some practice to make sure the pins actually touch the board at the correct position, and make sure that the cables don’t move while flashing.
    Tuya Smart High Power Switch for Boiler Water Heater

    Flashing:
    so, after wiring everything, and double checking that all connections are correct, it's time to run the flashing!
    when running the flashing command, you need to reset the chip by grounding pin 1 (that's the 'free' orange wire in the picture). if all goes well, you will get a successful msg!
    Tuya Smart High Power Switch for Boiler Water Heater

    OpenBK7231N config:
    by now you should see a new wifi AP from the switch, something like OpenBK7231N_#######.
    connect to this wifi, and setup access to your home wifi.
    in the configuration menu, setup:



    pintypevalue
    p6Rel1
    p7LED1
    p24Btn1

    Tuya Smart High Power Switch for Boiler Water Heater

    Cool? Ranking DIY
    About Author
    yarix2
    Level 3  
    Offline 
    yarix2 wrote 5 posts with rating 5, helped 0 times. Been with us since 2022 year.
  • #2
    gulson
    System Administrator
    Thank you very much for the presentations!
    I am curious if the relay will be durable and if it can switch 4400W.
  • #3
    p.kaczmarek2
    Level 27  
    That's a very interesting device. Thank you for posting the teardown.
    I am especially intrigued by that WB3S/CB3S switch. I have looked at the Tuya documentation to check the difference:
    Tuya Smart High Power Switch for Boiler Water Heater
    It seems that the jumper allows you to select between RXD2 and PWM3.
    For CB3S, those are pins 12 and 13:
    Tuya Smart High Power Switch for Boiler Water Heater
    Quote:

    12 CSN I/O Production test control pin. If it is used as a common I/O pin, it must be connected to the VCC externally. Do not connect it to the ground before the module is powered on.
    13 P8 I/O GPIOP_8, which corresponds to P8 of the IC, PWM 2

    It looks like they are trying to avoid using CSN pin in case of CB3S.

    Regarding 20A relay - it seems there is indeed such a relay inside, but I don't know how it will work in practise.
  • #4
    yarix2
    Level 3  
    thank you for this framework!

    Quote:
    "Regarding 20A relay..."
    - this part scares me the most!
    i hope this device is more reliable than Sonoff 16A... (i was lucky to be at home when it started burning)

    Tuya Smart High Power Switch for Boiler Water Heater
  • #5
    gulson
    System Administrator
    yarix2 wrote:
    Sonoff 16A... (i was lucky to be at home when it started burning)

    it's terrifying
  • #6
    ppprokurator
    Level 11  
    Have you considered using a contactor as an actuator that would be driven by sonoff?
  • #7
    ACCel
    Level 22  
    I used the Gosund SP111 socket for the 3kW 1F heater, it did not get extremely hot, but I did not use the disconnection too much, more of energy consumption monitoring.


    Tuya Smart High Power Switch for Boiler Water Heater
  • #8
    krzbor
    Level 24  
    In my Sonoff Dual the relay that controlled the 2kW heater stuck together. This is what it looks like after the conversion:
    Tuya Smart High Power Switch for Boiler Water Heater
    Tuya Smart High Power Switch for Boiler Water Heater
    and now it works.
  • #9
    ferbulous
    Level 11  
    Anything else you need to do find the pin for button?
    I have a similar tuya 20a switch (UK size standard) with wb3s, found the relay and led, tested remaining pins but still couldn’t get button working
  • #10
    p.kaczmarek2
    Level 27  
    Well, there are two approaches for finding the button. First is to try each pin one by one (set it to btn role In config and try pressing button and see if relays switches) and second option is to follow the PCB tracks with multimeter.
    Remember to set the channel index for button to the same value that relay has. Channel index is used to link relays, buttons and LEDs together.
  • #11
    lopr_pol
    Level 27  
    Well, do not expect that you will pull what is written on the Chinese relay. You have to divide it into 2 or better into 3.
  • #12
    yarix2
    Level 3  
    and there is a 3rd option, to try one of the pre configured "quick config". i tried the 4 gang switch and then removed the none-working buttons. Tuya Smart High Power Switch for Boiler Water Heater