Thermoelectric Module Keeps Printer Filament Cool And Dry

Anyone who has left their car windows open during a rainstorm will tell you the best way to dry the upholstery is to crank the AC and close the windows. A couple of hours later, presto — dry seats. The same can be said for 3D printer filament, and it’s pretty much what [Ben Krejci] is doing with this solid-state filament dryer.

The running gear for this build is nothing fancy; it’s just a standard thermoelectric cooling module and a fan. The trick was getting the airflow over the module right. [Ben] uses two air inlets on his printed enclosure to pull air from the cold side of the Peltier, which allows the air enough time in contact with the cold to condense out the water. It also allows sufficient airflow to keep the hot side of the module from overheating.

Water collection was a challenge, too. Water always finds a way to leak, and [Ben] came up with a clever case design incorporating a funnel to direct water away. The module is also periodically run in reverse to defrost the cold side heatsink.

The dehumidifier lives in a large tool cabinet with plenty of room for filament rolls and is run by an ESP32-C3 with temperature and humidity sensors, which allowed [Ben] to farm most of the control and monitoring out to ESPHome. The setup seems to work well, keeping the relative humidity inside the cabinet in the low 20s — good enough for PETG and TPU.

It’s an impressively complete build using off-the-shelf parts. For a different approach to solid-state filament drying, check out [Stefan]’s take on the problem.

53 thoughts on “Thermoelectric Module Keeps Printer Filament Cool And Dry

  1. “Anyone who has left their car windows open during a rainstorm will tell you…”

    Leaving the car windows open during a rainstorm only leaves the seats wet, but… leaving the car windows open during normal weather will cause you radio to be swiped, your navigation to be embezzled, you CD collection filched, which causes your eyebrows to be lifted but only to find out that your tapes are also hijacked and your phone charger has gone, the airbags poached, spare change for the meter might be misappropriated. Almost certainly you sunglasses will be pinched and your jacked purloined. Anything else that isn’t robbed or snatched from your car will most certainly be swiped some other time (if you don’t close that window).
    Any way, never leave you car window open (unless it rains) or the contents of your precious car will most certainly be stolen (for lack of another word), that is, if your car isn’t stolen as well. Close those windows people!

      1. Interesting suggestion, please name one

        However… after typing the comment I realized I might have left my car window open, so I went back to close it… but it already was too late. I did was in time to see my car going round the corner but it wasn’t me driving it. So the option of moving to another country just went out the window. And then I noticed the front door closed itself behind me, with my keys on the kitchen table and my spare keys in my car… Looking up I noticed that dark clouds are forming, so I guess it will be raining soon. What a day.

        1. Japan. It’s the only place in the world though.

          My wife has problems keeping track of her stuff and left the following in places:

          – cell phone x3
          – wallet x2
          – daughter’s bear

          Got em all back where they were left. The bear was turned into a police station.

          1. I think a citation is required.
            The places that have the lowest crime rates are also the ones you probably are thinking about moving to and frankly Japan is not one of those places. It’s like middle of the road. Certainly exponentially better than the US, but Theft and other crime only put it 27th best. Singapore, Belize, UAE, Thailand, Dominican Republic and Jamaica have lower crime rates and are also places I’d consider. TLDR; Japan is certainly not “The only place in the world”

          2. I once left $6,000 worth of camera gear on a bench in a train station, got it all back the next afternoon, nothing was touched. (The railway company was even nice enough to forward it on to a larger station where it would be easier for me to pick it up.)

          1. Thank you! Finally somebody who gets the yoke.

            For those of you who didn’t, the joke started with putting as many acronyms for the word “stolen” into one single reply. However, I do live in a normal city with normal crime rates, but leaving a car window open at night is asking for trouble, perhaps not instantly, but eventually it will. A long time ago a friend of me never locked his car at all, he stated that if a thieve stole his belonging, he would be able to find the thieve and learn him/her a lesson. Then I asked him if the potential thieve would also know that… Funny thing, he always locked his bicycle which didn’t prevent them from being stolen he also never found out who stole it.

    1. Unless of course they decided to put electronics in a cavity under the seats, in which case they’re toast. And in such horrible places where they steal anything not nailed down – I fully expect if you do nail things down they’ll just steal the nails too.

  2. Despite the hideous efficiency of TEC modules, there is genius in this approach.

    TECs are horrible at moving much actual heat: At full rated power, to move a 10 watts of heat uphill 25 degrees C, you need to dump 50 watts on the hot side. The hot side heatsink needs to be huge so the hot side of the TEC stays at a reasonable temperature.

    The genius here is that he doesn’t use it to move much heat at all: The goal is just to have a cold surface to condense on. By keeping the airflow on the cold side very low, he can run the TEC at a third its rated power and still get the cold side to freezing, largely because he doesn’t need to move very many watts.

    Great idea.

    The only additional thing I’d add is a heat exchanger: incoming air to the cold side should exchange heat to the air exiting the cold side. A 3-D printed gyroid-like infill pattern can work great for that.

    1. It looks like this thing does have success with just lowering the dew point below freezing, and maybe maintaining a cold spot in a fairly evenly warmed area is the best you can do without being able to make a closed loop of air in the cabinet. I suspect it is a decent approximation of a number of imaginary better ideas.

      But a TEC can do a bit better on efficiency at very small temperature differences and moderate power, as well as at higher absolute temperatures, so I thought like you about heat exchange and such. It seems like a heat pump dryer may be relevant, as you can move latent heat from condensation at a minimal temperature difference. Maybe it’s just that it’d have to get too warm before it could drop the dew point enough that way. Not sure if it’d help any to make sure the cold dry air goes over to lower the hot side temperature, reducing the delta, or if the two airflows in one cabinet thing gets it done well enough.

  3. Though I’m kind of surprised it doesn’t perform better, or that silica beads didn’t.
    My drybox is an old minifridge with its magnetic seal door, and with a heater in it that keeps it at 27 C. I use silica beads in Mason jars with window screening in place of solid lids.

    5 jars, about 1 kg of silica beads, keeps my box at 7% humidity. I regenerate every couple of months by baking the mason jars at 120 C for 3-4 hours. I never have to handle the beads themselves, just the jars.

        1. Wouldn’t you be better off with one of those baking tray with storage lid type concepts? Drilling a few holes in the lid to allow airflow for use and take it off to regen – much less glass and greater surface area of silica and the lid effectively becomes the shelf surface. I know IKEA does 1L oven safe glass with clip on and I think Bamboo lids as well 20x15x8 cm or something with the lid on (estimate/recall from memory having recently walked through while looking for an instant project box). All you’d need is to put a few holes in the lid.

          That said I’ve so far always just put the beads into one of those drawstring mesh bags for fruit and veg and then tipped them onto the baking tray to regen (easy not to spill any as the bags open wide enough to slide the the tray into before you tip em out). Gives a good mix of custom weights of beads for each location, rapid drying time and its easy to agitate them around if the sack is very full to get more work out them.

          1. Sure. Sounds great. I just don’t happen to have one of those “baking tray with storage lid type” that I have never seen. I dance with the one I got.

          2. Fair enough Paul, I didn’t know they existed either till I was wandering around IKEA hoping to get a good project box for a fairly rushed job. But being such a good idea I figured most folks probably would know they exist and I was just late to the party.


            As an example, and boy were my measurements close to the reported ones. Nice to know my memory does still work for inane and useless detail of something I don’t much care about I guess.

    1. I’d have to point out that is kind of overkill for filament drying in general, plus I’ve never seen an off the shelf AC or Heat pump with a compressor nearly as small the whole package here and that is before you add all the other cruft, so form factor wise you’d have much less space for your filaments. Then there is the noise issue – peltier are effectively silent unless the drive electronics whine.

      Seems to me like this is one of the few locations where a peltier element is just better for the task.

  4. I have dozens of rolls of filament stored in an un air conditioned work shop in humid Louisiana.. been using them for years with no problem. I don’t understand why people go to such great lengths to store plastic.

    1. It depends heavily on the type of plastic as well. Certain varieties (Nylon and PC come to mind) become problematic to print almost immediately if they get moist. If you’re mostly doing pla, you might not notice the moderate degradation of the mechanical properties, and maybe just a little more stringing than you’d get otherwise. It does make a definite difference however.

    2. Nylon, PC, PET are all extremely hygroscopic and will absorb moisture to the point of being unprintable within a couple of hours in a humid environment. Higher end engineering plastics like PEEK, PEKK, PEI are even worse.

      PLA and some (not all) ABS have lower hygroscopicity and so don’t need much in the way of special handling unless they’re left sitting out in the humidity for a long time.

      If you do deal with PET(G), nylons, PC etc you might like to try drying your filament before printing to see if it makes a difference, you might find an increase in quality almost for free.

    3. Just because you haven’t experienced it that doesn’t mean it doesn’t happen.

      Moisture absorption is a well known issue with plastic in general, even when injection moulding they sometimes have to dry the pellets.

      It also depends heavily on which materials you use, some like PLA don’t absorb much moisture and take a long time to do so, others like nylon absorb lots of moisture very quickly. So what materials do you print?

      Even after printing moisture can be an issue, mainly with nylon or fibre reinforced nylon. The part may come off the printer stiff and strong but within a few days in a normal environment it will get more flexible and weaker or you can soak it in water to speed this process up.

      It also depends on your printer, skill level and tolerance of defects. It is still possible to print with wet filament, you just don’t get good results, if your printer isn’t very good or you don’t expect much quality then you might not notice a difference if the filament is wet.

      You can tell if a filament is wet by extruding it, if you hear little pops then it is wet. Being wet can cause a large number of issues, lower print quality, lower print strength, it can degrade the material, it can string more and things like bed and layer adhesion can be worse.

      If you don’t understand why people go to such lengths to store plastic then just look online at forums and see the number of people who have had unknown and undiagnosable issues with their printer until they dry the filament.

    1. Heating air does not lower the amount of water in it. It just increases the amount it COULD hold.

      Judging by the content of that comment, I’ll assume Fahrenheit will be more relatable, so: At 70 F, Air can contain up to 1.58% water: any more will condense out as fog. At 50% relative humidity that air contains 0.79% water. That’s 0.0079 pounds of water per pound of air, if that’s more relatable.

      The same air, warmed to 90 F, will contain the SAME amount of water, 0.79%. But, because warm air can dissolve more water than cool air, 90 F air COULD contain up to 3.1% water, so we say that 0.79% is now 25% relative humidity, even though it still contains the SAME amount of water.

      1. Comercial filament dryers just use heat and fans, they work because of the difference in relative humidity in air.

        Imagine an ambient air with 25% humidity at room temp.
        When the air heated in a filament dryer, the air becomes relatively dryer and moisture migrates from filament to air, the air is (slowly) replenished so the warm air that now contains more (absolute) amount of water is replaced with air from outside the box

      2. You are using that hotter air that can hold more water, at lower relative humidity, to draw the moisture out of the filament. You are drying the filament, not the air.

      3. You’re coming across as condescending to the first guy without conveying the logic of why making the filament warmer than the dew point may not dry it, unlike with a towel or glass or something.

        Normally, warming the object up and letting the warm moist air go away to condense elsewhere is enough. But with a hygroscopic substance, which appears to include some filament types, water is absorbed even at much lower relative humidity than 100%. Or to put it another way, the filament is at a much higher temperature than the dew point yet it still absorbs water. And you can’t just get it as hot as it takes, because it’s filament. So to do it, this project uses a very cold spot to condense the water, and that way there’s enough of a difference that the water is still encouraged to leave.

          1. One kinda needs to have a gut feel for the numbers for hot&humid weather flying (for calculating density altitude) but I have not needed to do that for a few decades so, yes, I had to look up the actual values.

  5. Great project, Ben! I’ve been contemplating something like this for years myself but never got serious about it.

    One note: It sounds like it’s working fine for your needs as is, but you can get lower relative humidity simply by dropping the temp of the cold side. A dew point of -0.5C translates to about 20% RH at 25C. If you go colder though, more water vapor will condense out. A dew point of -10C would mean 10% RH at 25C.

    The dew point is basically the temperature at which water molecules are condensing and re-evaporating at the same rate: It’s an equilibrium. The lower the temperature of the cold surface, the slower water molecules re-evaporate, so it takes fewer of them floating around in the air to balance out.

    That’s a poor, hand-waving explanation, but the bottom line is that the colder the surface, the lower it will drive the RH in the ambient-temp air. – If you want to get really crazy with it, a temp of -35C will get you to 1% RH at a 25C ambient.

    (Actually, just warming up the air inside the box will also drop the RH for a given dew point: If you warmed the air inside the box up to 36C, your current cold-side temp would mean just 10% RH at that higher ambient.)

  6. It seems this is only good for keeping filament dry, not actually drying it. Everything I have seen to do with drying filament other than this relies on heat to do so, with heat even improving results in a vacuum chamber and the temperature you dry it at having a large impact on drying time.

    If this is just a fancy dry box then wouldn’t it be much easier just to use an airtight box and some dessicant?

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