Actuator Opens The Door To Drier Dishes

Dishwashers are great at washing dishes and even rinsing them, most of the time. Where they tend to fail is in the drying part. Somehow these things dry hot enough to warp stoneware dishes, but not so well that things are actually dry when you open the door. Blame it on the lack of air movement.

Ideally, the dishwasher cycle is started soon after dinner time so it can be finished and opened up before it’s time for bed. But if you do that, then you miss all the dishes from late-night snacking and the occasional wine glass. Wait until bedtime to start it, and it has to sit several hours with moisture inside. Obviously, the answer is to listen for the victory beeps at the end of the cycle, and use a slow but forceful actuator to push the door open.

[Ivan Stepaniuk] is listening for the dishwasher’s frequencies with a microphone, amplifying them with a trusty LM386, and using an STM32 blue pill to crunch the audio. [Ivan] has plans to incorporate an ESP8266 board for IoT, presumably to get a notification when the door has been opened successfully. Check out the demo after the break.

Yes, dishwashers are great until they aren’t, and some little part breaks. But why pay for a new detergent compartment cover when you can just print one?

40 thoughts on “Actuator Opens The Door To Drier Dishes

    1. So does my 5 y/o Samsung. It came with a foil barrier to mount under the counter. Otherwise, it would steam the wood on the bottom when the door pops open.
      It all works well, despite the very thorough hypothesis to the contrary in the comment below.
      We do call it Creepy Dishwasher though. There is a long, silent cool down before the door latch pops then creaks open. Usually when the house starts to quiet down in the evening. Someone inevitably calls out “Creepy’s Done!”

      1. Many dishwashers come with that barrier anyway, because there’s no difference between a human opening the dishwasher after a cycle and it happening automatically. The latter just happens more consistently.

  1. Just wait until it’s done! Opening the door early is not only pointless, but counter productive.
    The drying process relies on a temperature gradient inside the dishwasher from the still hot dishes to the outside walls. If the dishes are hotter than the outside walls the water will evaporate from the dishes and condensate on the walls. This condensation frees the energy that was bound by the evaporation and the cycle starts again. It is basically a heatpipe transporting the heat from the dishes to the walls. But it is a slow one. Just wait.
    By opening the door you release all that energy that is bound in the steam and stop the drying cycle. Now it needs a lot of external energy (from the room heater) and time. And all the humidity ends up on the house walls instead of the inside walls of the dishwasher and into the drain from there.
    Maybe the root cause for the drying problems is more like a mostly empty dishwasher? It requires a certain thermal mass to workout.

    1. In the winter we have to work hard to put extra moisture into the interior air, so a little extra is welcome. Are you really going to set an alarm for 2AM so you can get out of bed to open the dishwasher?

    2. I’d like your dishwasher – our Miele is hopeless at drying. In the winter we have the wood fire burning and sucking all the moisture out of the air. The quickest way(only way ) to dry is to open the door – we don’t have a disgusting cat in the house so no chance of that spoiling the dishes .

      We run out dishwasher during the day when the solar system is pumping bout sufficient power to cover the energy requirements of the washer to reduce the energy bill.

    3. That’s illogical. You’re suggesting a closed chamber with high moisture content and poor thermal gradient at its boundary is better at removing moisture from a surface than taking that hot surface and putting it into cooler, convective unsaturated air.
      This is demonstrably not true by the fact that every day, if I forget to open the dishwasher, 4 hours later everything is still wet, but if I open the door it’s all dry in 30 minutes, and it took no more energy from the house as the pots (and residual water) are hotter than the environment.

        1. it might be that in sime climates…I guess cold ones, that after the unit turn its water heaters off at the end of the washing, the unit’s case and walls will cool before the dishes will due to their greater thermal mass. This will mean the moisture on the dishes will condense on the outer walls and run down to the sump until both the dishes and the unit’s walls are below the dew temp differential. But if you’re in a warm climate the dw case won’t cool down enough to break through the temp differencials needed for the moisture to condense on them…. leading to wet cold dishes. But really, is it so hard to pop the door on your way to brush teeth or loo

      1. +1 THIS. No need for an engineering degree either; if you leave the door closed, the moisture condenses back onto the dishes. Leave it closed for a whole day and it will even start smelling not-so-clean.

    4. Sorry, but that is entirely nonsensical. “Opening the door releases the energy and stops the drying cycle”?? The energy for drying is in the *dishes*, not in the humid air. In fact, when the unit is sealed the humidity will stay at 100% and no more *can* evaporate. Extracting the humid air and replacing it with dry air is the only way to efficiently use the remaining heat in the dishes to dry them to completion.

      1. The trick is to make sure that the stored energy is used for drying only. If you open it, most of the heat just heats up some air that goes into the room. The dishes cool off faster than the water evaporates. Then you have half-dried, but cold dishes. Sure, they still dry in the room air eventually. But all the moisture goes into the room.

        The humidity inside is constantly at 100% because every single little drop that condensates on the (slightly cooler) walls is replaced by water from the (slightly hotter) surface of the dishes.

        And when there is no more water to “refill” the air, it still cools off further and more water condensates on the walls. Not on the dishes, because they are still the hottest surface around. And yes, that means the humidity stays at 100%. But there is no (big) risk of mold because everything got sterilized while running (The water is pretty hot. Even 45°C kills most things and the soap destroys many spores). At least sterile enough to keep your things safely in there overnight.

        The dishwasher in this house here is from the 70s, nothing new or fancy. And it dries beautifully (except for plastic, of cause). And so did all the other dishwashers I used so far, dating from the 70s to 2000s.

        But there seem to be a fair number of people having different experiences. I wonder why? Really bad dishwasher design (missing insulation?), half empty?, plastic dishes? Any ideas?

        1. I can tell you my experience (I built this thing). When the dishwasher beeps, the dishes are practically dry, it beeps several minutes after it finished the actual washing cycle.

          The problem is what happens afterwards. Like you very well say, humidity condenses on the walls, but when the whole system reaches thermal equilibrium, a compartment with wet walls and bottom is not where you wanna keep your clean dishes.

          As you correctly sayand can be seen in the demo video, opening the door lets some of the heat escape, but the dishes, like @pelrun says, are still pretty hot. The droplets that might have survived the initial (door closed) drying cycle evaporate much faster this way than inside the closed, 100% saturated environment.

          Then there is the empirical evidence: this really eliminates water marks on dishes on this entry-level dishwasher. + lets me run it even if I know I will be out of my place the whole day.

    5. Sorry, but this is complete hogwash.
      Not only is my kitchen a lot colder than the walls of my washer, it is also a lot drier.
      So not only the temperature gradient is larger, so is the water concentration gradient.

  2. I have a really hard time understanding the problem.

    My 5+ year old Siemens doesn’t open up, but for the last 20something minutes I doesn’t do anything, I assume it’s just to let the dishes dry. When I open it up afterwards the dishes are too hot to touch but they’re properly dry and I could store them right away (but I usually don’t and just “live” out of the dishwasher).

  3. Funny… Our 45-year-old Kenmore simply turned on a vent fan at the end of the cycle. No problem. Worked perfectly. It also had an internal heater you could optionally have it turn on to speed the process if you were in a hurry. It even had a “dish warm” feature where you could run the heater/vent cycle separately to warm a load of clean dishes for (like, for Thanksgiving dinner). Fantastic dishwasher. It was even one of the cheapest at the time. Bonus: you could flip the front panel to choose between glorious Harvest Gold or Avocado!

    When I asked an appliance salesdroid about that vent & heater feature for our new house’s dishwasher they answered that the enviro-driven efficiency mandates killed those features. The thing is, in real terms I’m paying about a quarter as much for electricity now than it cost then. Efficiency be darned.

    And yes, that “condensation drying” stuff is bunk.

  4. You mean your washer doesn’t have a timer?

    It’s cheapest to run it in the early morning hours anyways, or in some places right in the middle of the day. Either way, you’ll have the dishes ready for when you wake up, or come home from work.

    1. Oh bummer. The LM358 has some brutal crossover distortion.

      Just went looking for a citation, b/c that’s the kinda guy I am, and stumbled on this awesome video, where the crossover distortion is not only documented nicely, but also eliminated by putting a (hefty!) load on the output to keep one set of output transistors always on, solving the problem. Cute trick, if not exactly friendly to your output impedance.

      1. Nice to see the clean demonstration of the effect. That behavior is clearly stated and and its fix recommended in the datasheet:

        “To reduce the power supply currentdrain,the amplifiers have a class A output stage for small signal levels which converts to class B in a large signal mode. […]
        For ac applications, where the load is capacitively coupled to the output of the amplifier, a resistor should be used, from the output of the amplifier to ground to increase the class A bias current and prevent crossover distortion.

    2. Indeed, the post is 27 LMs off. The LM358 is just for the microphone preamp. It took some effort to keep the MCU and Wi-Fi noise out of the audio signal. I will eventually post the circuit.

  5. Ummm… people…. you’ve provided many common-sense, plausible solutions to the wet-dishes problem (yawn).

    This, however is Hackaday, and “just remember to open the door” does not involve a linear actuator, an LM386, or even a 555. Automatic disqualification!

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