It heats up. The water vapor gives up energy when it condenses. Here’s what it looks like in the infrared. It surprised me it’s enough heat to see but it’s actually a very small temperature increase.
This was after running about 6 hours.
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That is exactly what I’m doing.
Perfect size air tight box, priced between $19 and $24 for 4: amazon
Disposable hygrometer, $10 for 6: amazon
100g silica gel pack, $1.70: amazon
Spool holder: makerworld
And to print, I transfer the abrasive filaments to a Sunlu heater and crank the heat while printing. For the rest, I transfer them to my dry AMS.
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I appreciate it. This is exactly the way I decided to go. I think those containers aren’t perfect but close enough to what I’m looking for and will fit my shelves. Only difference is I ordered the round hygrometers. I won’t be feeding out of them - strictly storage.
I remembered this image, and couldn’t find it, but I finally found it again:
Here’s the source: Best "GoTo" Filament - #15 by user_482380812
Not sure what those round containers are, but they look a lot like the printdry containers:
at about $12.50 each, or roughly 3x a cereal container. They do stack rather nicely though, and perhaps (?) they have a better seal. Not sure.
At some point I’m going to test various containers for moisture leakage. Extremely preliminary measurements on the cereal containers are: about 0.1g moisture intrusion per day. Not sure if that’s through the seal or the plastic itself. The plastic may seem improbable, but it has a much larger surface area, so I wouldn’t rule it out. I’ll probably try a stainless steel container with a silicon gasket and see how that compares. It would be a big win if a simple cookie tin could do the job, as those are super cheap. They seem to keep Danish sugar cookies dry, so why not filament? Maybe $1/each, or “free” with cookies. Worst case: seal it with non-China metal HVAC tape that meets a NIOSH standard for ductwork, and you’re probably guaranteed to come out ahead. Still… I’ll wait for the data, and then we’ll know for sure. 
One of my favorite quotes from “The Imitation Game”:
The Americans, the Russians, the French, the Germans, everyone thinks Enigma is unbreakable. Alan Turing : Good. Let me try and we 'll know for sure , won’t we?
I’m no Alan Turing, but… I like the idea that you don’t know until you devise an experiment to decide the matter definitively. I wish more people would do that. It would spread the workload considerably!
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I use these bags too but I have heard of people using 4 litre cereal containers from amazon.
How I store, dry, and keep dry my filament:
I use these cereal boxes (@KenB-in-NC As of yet I have not noticed material fatigue of the flap hinges of the lids) with these hygrometers. I use those hygrometers specifically because they have a relative humidity range of 10% - 90%, whereas many other brands only go down to 20%.
I use this activated alumina in bulk, which I fill into nylon mesh bags, and avoid the whole time and effort of printing dessicant boxes and contraptions for the cereal boxes, because all I want is a cheap and easy dry storage solution. (Buying in bulk and filling nylon bags is a much cheaper solution than buying pre-filled bags of silica gell dessicant, my previous solution.)
When I get new hygrometers, I test them in a cereal box with copious amounts of dessicant along with a known good hygrometer, to see if they actually go down to 10%. Some don’t make it down that far; they get returned. In the image below, there is one unit that does not read below 14%:
If I need to print from a drybox (eg. TPU), then I use the PolyMaker Polydryer, printing directly from the box. In the image below, one can see a freshly opened Bambu PETG HF spool in the dryer:
The dry boxes have their place below the print station:
As one can see in that last image, taken about 20 minutes after the previous image of the PolyDryer, the RH in the PolyBox (containing the blue PETG HF) is sinking. If 6 hours doesn’t do it, then I’ll run it for another 6 hours. Ideally I want to see it at 10%. Then the spool either stays in the PolyBox, or it goes into a cereal box until it’s time to print.
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I do like those cereal boxes. They seem pretty tight and I’ve been weighing filament into and out of them. The spools pick up maybe 50mg of water weight in them which I think is from the air inside the box and the short time between the scale before it goes in the cereal box. They seem quite tight.
Also like that PolyDryer. Do regenerate the molecular sieves or just use them until spent?
Nice setup, btw.
Hi MZip, thanks.
Yes, the PolyDryer is great! And I do regenerate the activated alumina, in the kitchen oven. Since it has no indicator, it is kept in use until the RH rises above 15% - 20%, then it gets dried.
To give more reference points of my setup:
In the room with the filament, the RH is kept at 45% (this is not what we have outdoors right now, which is 80% RH). With 50ml of activated alumina in each 4l cereal box, a Bambu PLA Basic/Matte spool dried to 10% RH (meaning it reads 10% RH in the PolyDryer or in the cereal box) will keep that RH for over a month – with the “occasional” opening of the cereal box, the “swift” removal of the spool and immediate closing of the box, the spool being returned after use in the AMS.
The AMS is also kept at 10% RH (or less, but the hygrometer will not show less than 10%).
If not openening the cereal box at all, the RH in the box will stay at 10% for a good two months --but I can’t say it’d last longer, because at some point the cereal boxes are opened enough that the humidity doesn’t go back down to 10% shortly after the lid is closed.
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@ RenHoek Not sure what brand cereal boxes you are using, but they look very similar to the Yashe Store brand I got. If they are made of the same material, the latches should last you a good long time. The Yashe Store boxes have very good seals on them. I hope I didn’t imply that they would break quickly - quite the opposite, they are very much like Snapware food storage containers, and they last us a few years with very heavy use. I doubt the cereal boxes with filament will see as much opening/closing as kitchen Snapware!
I also envy you the great setup you built with your printer above and filament storage below. Wish I had the space here to do so. (Old people downsizing for retirement is not all its cracked up to be LOL.)
Do you make your own nylon mesh bags for the desiccant or do you buy the bags and then fill them? Love to hear more about that.
I’m seeing very similar stuff. It’s kind of surprising how much filament likes water and just an open/close cycle has such an effect.
That PolyDryer is pretty cool, too. You’re drying to an indicated 10% or higher (20%?) when the alumina gets loaded? (And know the 10% measurement floor) What temperature do you dry PLA? And how many spools before you have to change the alumina in the dryer?
Good information!
@RenHoek At what temperature do you regenerate your activated alumina, and for how long? I can’t find anywhere where WiseSorbent actually recommends. I thought it would be in the TDS, but it’s not there:
I haven’t tried it yet, but I have the same 7.5 pound plastic jug of it as you have. It doesn’t say there either. Truly odd, because on the front of the jug it does say that it is “Rechargeable.” Surely they would know what’s optimal. Why force customers to call or email to get the information? I also have a jug of WiseSorbant Molecular Sieve, and on that the label does give directions for how to dry out the molecular sieve pellets, as one would expect.
Naturally I checked Google for other sources for guidance on the activated alumina, and the generic advice is:
180C to 350C is quite a range!
I only just now noticed in the TDS for WiseSorbant Activated Alumina that I linked above: it says the shelf life is 2 years. Huh? That seems awfully short. Unless it gets contaminated, I thought it was supposed to last forever. Do you have any insight into that?
Here’s one source online for regeneration of silica vs activated alumina:
https://www.oimchem.com/technical-article/activated-alumina-vs-silica-gel.htmlActivated Alumina vs Silica Gel-OIM Chemical
That source says 170-260 F for activated alumina.
Hi MZip and Ken and NeverDie,
Active Filament Drying: PLA on Level 1 of the PolyDryer (50C) for 6 hours normally does it, but maybe needs more. PETG Level 2 (60C) for as long as it takes. I have not measured the temperature in the box, tests online indicate the air temperature is lower (see My Tech Fun). I end up putting the spool in a cereal box with a fresh mesh bag of dessicant to get it to 10% to free up the dryer, meaning the spool is still emmiting moisture and the dessicant in the box is taking that up.
Activated Alumina Recharging: in the oven for 225°C for 3 hours. If that is enough will depend how much moisture it’s taken up, and the oven. Mine has a “4D air” mode which does a great good job of circulating the hot air instead of just baking from top and/or bottom. Builitmakeit have a very nice write-up of their setup for print spools, the dry temp/time jibing with usage reports in labs I’ve seen on Reddit. (As an aside, a simmilar commercial spool insert is available for quite a hefty price from Slice Engineering). Slice Engineering also lists recharge time for 250°C (480°F) for 2 hours|
Mesh Bags for Dessicant: The idea to use a nylon/PE bag I got indirectly from the Builditmakeit build where they use wire mesh. He makes an all-metal spool-center insert for holding the activated alumina in the spool, which is put directly in the oven (nice idea, too much work for me --I needed a simpler solution, one that just stays in the cereal box).
The wire mesh gave me the idea to look for reusable bags for the dessicant. There are descriptions of using organza gift bags for dessicant, but I wanted something more robust, and re-closable, ideally with a zipper → Filter Bags used for aquariums, are cheap, re-closable, and come in all sizes.
I have several types, with finer and coarser mesh. Since the activated alumina beads are much larger than even coarse silica gell, it’s possible to use coarser mesh as well. So far I have not directly compared the the efficiency of a finer to coarser mesh. Probably, if both work fine in an aquarium to filter water, then any mesh will have good enough air permeability as well.
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Thanks, Ken. I’m not sure why you picked that particular source, but it turned out to be useful.
- It turns out they make different kinds of activated alumina for different purposes, and those different varieties are dried at different temperatures. So, this explains the wide temperature spread that I had asked about. Mystery solved.
- They more or less state that if a client’s desire is to get the very driest drying using desiccant, especially if the goal is to do so at high temperature, then they think molecular sieve is the best choice–maybe the only real solution that can satisfy both requirements:
Looking at the directions on my jug of 3A molecular sieve, the recommended regeneration protocol is 2 hours in a “muffle oven” (whatever the heck that is) at a temperature of 550C. That’s 1022F. Then afterward transfer to a cooling vessle–I presume to keep ambient moisture from re-infiltrating back into it by isolating away from it.
I’ve looked on Aliexpress, and the least expensive muffle ovens are around $400-$500. If I were to go that route, then I’m guessing I would use molecular sieve for everything as more or less “the one desiccant to rule them all.” Is that even possible, or does anybody reading this post foresee a gotcha standing in the way of that?
Just to clarify, you are drying PLA at 50C for 6 hours in that dryer. Is the RH% at 10% (indicated) in the chamber or above that? So you aren’t drying to a chamber humidity?
Do you see RH% spike when you put in a roll of filament to dry?
The reason for the questions is I see a number of things when I put spools in my drying rig and am trying to get a feel for details in how a recirculating dryer works.
Thanks for this!
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Glad you found it helpful! I picked that site because I was investigating the difference between the two desiccants and it seemed (to me) to do a good job in that.
I looked at the Polymaker Polydryer on Amazon, and it got very negative reviews, so I shied away from purchasing one. I already have the eSun eBox, and for the PLA that I had been using (in my more novice days) it seemed to be OK. Wouldn’t rave about it, but it sufficed.
On a slightly different note, if price is not restrictive to your budget, you might want to consider the GoveeLife Smart Thermo-Hydrometer 2-pack on Amazon (GoveeLife Smart Thermo-Hygrometer 2-pack
They are bluetooth enabled (for those diehards who believe everything is better with bluetooth!) as well as having a operating humidity range of 0-99%. Pricey at $32 for 2-pack, but right now you can get 45% off on Amazon. They are VERY nice units, exceptionally clear displays that are easy to read, and the push button on top changes between F and C. Not sure I would invest in one for each of my storage boxes (which number >50 at present) but I keep one in my AMS in an unused spool slot.
Hi,
yes RH goes up rapidly when the cereal box is opened, essentially to the RH of the room air. In my case that’s 45% RH.
I find the PolyDryer very functional. I would never trust an Amazon review, positive or negative, without seeing some information from other sources. I got mine from 3DJake. I dry for 6 hours say, or 12 hours at a temperature appropriate to not melt the filament, and do not get it to 10% in the dryer; that happens afterwards in the filament box.
@KenN-in-NC, I think you asked about the AMS: it has four printed dessicant containers plus the two standard pockets in the bottom. The spools don’t really have a chance to absorb anything when the lid is briefly opened. As with the filament boxes, the RH rises and goes back down to 10%. It’ll last way more than a month before it starts to settle back at > 10%.
For the Bambu Studio / App / Orca AMS Display all this is “one drop” of water. For Bambu I guess that’s all considered totally dry. 
Someone also asked: when does the activated alumina get recharged? Somehwere between 15% and 20% RH. Meaning, I wait till I have some “wet” dessicant amassed, and when I have enough to want to turn on the oven, then it’s time.
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When did you get your AMS unit? I ask because I got mine (as well as the P1S) recently (late June 2024) and it doesn’t have those 4 printed desiccant containers you show. All it has is two bays in the bottom at the back that came with desiccant packs the likes of which I never saw before. (They seem to be one piece, folded in half and glued to one another.) There is no place to have those 4 hanging desiccant containers.
I just looked on MakerWorld and I see someone has a model for desiccant containers that fit between the four filament feeders (so you can fit 3 in). I then thought maybe my package was delivered missing those, so I went back and looked at the Bambu website and they show the AMS just as it was delivered to me; that is, sans desiccant containers.
Since I can not close the AMS lid fully due to the spools I am using (most are cardboard, which seems to be where everyone is heading, so I have a “universal spool” adapter for lack of better term that I place on each spool. That extra mm or two prevents me from closing and sealing the lid as the spool binds with the lid. So, I have to leave the lid sitting on the clips thus having the lid open a few mm. The best I am getting is down to 34% inside at 85 F. I just may print off 3 of those desiccant containers and wedge them in between the filament feeders.
As more and more filament vendors are using cardboard spools, and Bambu AMS says to NOT use cardboard spools, its going to be interesting in the very near future. I printed (3 times) a spool winder, and have so many issues with its design that it is useless to me. I managed to spool about a third of a new spool of ABS onto a Bambu spool before the works got gummed up, and wound up respooling back onto the original cardboard spool by hand. That was the end for me. If anyone knows of a reasonably-priced commercial spooler, please post it here for me and others!
These style desiccant holders are designed to slip into the open area at the front of the AMS. They are a 3rd party add on you print yourself. Makerworld has a plethora of different variations.
Example:
Makerworld Reference for picture
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