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Arduino clothes dryer control?

Former Member

I have a clothes dryer with a stripped gear in the timer knob and had an idea to replace this time with an Arduino (or possibly even a RPi) and some relays.

 

I've taken apart the timer and all it consists of is 3 sets of contacts that are opened and closed in sequence as the timer slowly turns the knob.

 

I was thinking about replacing this unit with an Arduino, 3 relays and adding a rotary encoder and LCD to cycle through the different dryer modes.  I envision that my programming would simply switch the 3 relays open and closed in sequence that I would match with timing delays that mimic the original physical timer.

 

My questions are:

 

Does anyone see a reason why this would be bad or perhaps dangerous?  (all other circuit components- thermal switches, sensors, valve controllers and motor controllers are still in the system... the timer knob only seems to turn the motor, fuel valve and temperature controller ON and OFF)

 

Is there a better micro controller anyone would suggest for this idea?  I have a Raspberry Pi, but that seems like overkill for this application... to to mention, more complicated.

 

Lastly, can anyone recommend a reliable power supply I could use to power the arduino inside the dryer?  I can tap off the mains supply, but don't want to wire in a socket and have a wall wart inside the machine.

 

thank you!

 

Jay

  • 0

    I don't know.  But if you want the arduino info on timers and interrupts please read:

     

    Arduino 101: Timers and Interrupts

     

    http://letsmakerobots.com/node/28278

  • 0 in reply to billabott

    I have done something similar both to out ancient (beyond economic repair by a professional) heating boiler / furnace and a tumble drier. In both these cases there was just a single relay contact to close, so it was easier than this setup.

     

    I could see a big danger if say the fuel valve turned on and then no ignition occured until enough had built up for an explosion! So, really mke sure you know exactly what the existing system does.

     

    I was able to find online service manuals for my hacked appliances, which helped a bit.

     

    I used a redundant 5V phone charger, taken out of its wall wart box and put in a new box as a power supply, but I was using an 'off board' arduino. Wiring its AC input to the terminal strip where AC entered the appliances.

     

    Also, if you are embedding this permanently, then think about using an Arduino Pro of some species, maybe a mini would do?

  • 0 in reply to billabott

    Billabott - thank you for that link. This will be helpful in my design.

     

    Simon.monk - thanks for your reply...

     

    Luckily, the wiring schematic is nicely taped to the inside the dryer so I was able to see how the full system works.

     

    It appears the fuel value circuit is powered through the motor controller (looks by the schematic to be a double-throw relay or equivelant solid-state device)... If the motor is not on, then there is no power going to any other part of the system (except for the timer motor itself)... no running motor, no open fuel valve.  (The neutral for the whole system appears to flow through this motor relay.)

     

    The "Push to Start" button on the appears to start the process by powering up the solid-state "Elecronic Dry Control" (connects the neutral) which in-turn closes the motor control relay in a self-latching fashion and everything stems from there.  The one set of contacts within the timer routes line voltage to the motor control relay (and it's own timer motor) while the machine is running (open the door or turn the timer to "off" and the motor relay un-latches- everything shuts down).

     

    It appears that the other 2 sets of contacts inside the current timer do the following:  1: supplies line voltage to the "Electronic Dry Control" and 2: supplies line voltage to the temperature switch.  It is that last one that makes having a broken timer troublesome:  the dryer will run as long as I let it, so my clothes dry, but I am "over cooking them" because the heat never turns off until I shut down the dryer.

     

    It seems to me that the fail-safe in the system is that motor controller which, again, routes power to the fuel valve and everywhere else - whether it be a "stuck" microprocessor or a "stuck" mechanical timer, everything else would stay on or off accordingly.  (Even if the "temparature switch" were to be stuck in the ON position, the gas valve / igniter would not be on because it will have lost its neutral from the motor not being on.)

     

    Again, there also seems to be other safety sensors built inline with the fuel valve such as over-temp sensors and I am assuming "under-temp" (ie if it senses that the fuel turned on but never ignited - it would close the valve)

     

    I'm fairly confident that the dryer runs a really simple set of circuits and switching out the timer would be safe.. I am just curious if Arduino would be up for the task.  I will look at the pro-version you mentioned.  I have a few of "RBBB" kits that bought for another project that I never pulled the trigger on - that is what inspired me to think of Arduino or other microcontroller setup.

     

    Also, I have a couple of nice metel enclosures - I like your idea of taking wall transformer guts and putting them in a better case... If there was something I could buy that was already built to be use inside an enclosure and reliable, I would like to consider that as well.

     

    Thank you, again,

    J