I’m beginning to suspect there are no special sensors in the digital psychrometers, because i still can’t find any sensors in that price range on mouser or digikey that would suggest otherwise. 
I suspect they simply impute the dewpoint from an RH sensor, which at a low dewpoint most likely won’t have enough spread to be accurate. Good enough for hvac, but probably not good enough for our purposes.
I don’t much care about dewpoint until experience tells me otherwise.
My A/C unit puts lots of water into the drain and it’s nowhere near 0C. I’ll accept whatever happens at about 0C and call it good until I learn, via experience printing with my “dried” filament, that it’s not good enough.
The other reason is that going below 0C means ice forms and there’s no way to get rid of it short of cracking it off which would mean opening the chamber and ruining whatever dry air it had or waiting for the ice to melt to reintroduce water to very dry air, defeating the purpose. Ice is too much of a problem for my taste.
Hi! I Have a X1 Carbon + AMS. As an external source of filament, I’m using the SUNLU FilaDryer S4 (SUNLU FilaDryer S4, Best filament dryer- SUNLU official online store – Affordable 3D Printing Filaments and Resins).
It can hold and dry 4 rolls an has a built-in 300W PTC heater, heating to 50º C. It’s working fine and also serves as a storage box.
Hi Joe, the dryers work ok (with caveats) when ambient relative humidity is low. They seem to fall flat when ambient humidity rises. My Sunlu S2 started out apparently working great but as our humidity rose in June, it hit a wall. At least the Sunlu S2 doesn’t do much air exchange with the outside so spools sit and stew in their own moisture. Prop the lid open a little in a humid environment and it can add water. I found my S2 actually adds water to filament on humid days. I took rolls out of my AMS to dry them and when I put them back, the humidity spiked big time in the AMS - way more than just opening the lid to load a spool.
It looks like the only way to get these simple dryers to work properly is to feed them dry air or remove the moisture liberated from the heated spools. As long as folks are using them in low ambient RH environments they can work well. For me these efforts are more just to get me through the summer since our humidity is way up. The rest of the year, and especially the winter, are pretty dry for me and this extra stuff generally won’t be needed.
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Although I don’t own any commercially available dryer equipment, just by looking at the design with no air exchange to move moist air out, I knew that these devices were going to be incapable of dealing with my Caribbean tropical humid environment. I saw videos where drops of water were rolling down the inside of these machines with no exit.
The heating power of several hundred watts was the final straw that told me I’m not purchasing these poorly engineered products after I built a heating chamber to make ‘black garlic’ that used 30W to set and hold the chamber at 70C for 6 weeks.
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Through other conversations here I decided to spring for a low cost infrared imager. Very revealing when looking at the S2. It loses a lot of that heat through its walls. I designed up a new base for my earlier humidity tests and it added just enough heat load that I couldn’t maintain 70C in it with the extra air makeup my setup was providing. It was close though - it could hold 65C. I redesigned the base to have thicker walls and used honeycomb infill to trap air - printed insulation of sorts. It made a huge difference. Images of the base initially showed significant hot spots on a par with the upper part of the Sunlu. The base now is much dimmer with much less heat loss through it.
But the S2 itself just has walls that let out a lot of heat and not much in the way of ventilation to let out moisture. If these other efforts do get us a dry air source, though, I think we can really improve the function of these dryers. They won’t be perfect but they hopefully will work more reliably.
Buying something that’s inherently not fit for purpose is what I won’t do. If something works only under certain circumstances, what is one to do when those conditions are not available?
All the commercial dryers I looked at had the same issues. One company cooked up a poor solution and then the copycats decided to market their poor versions. Adding bells and whistles when the primary function is inadequate is putting lipstick on a pig.
No air exchange, no insulation, huge overkill on wattage, a timer to say when drying is done, inability to attain and hold high heat settings, cheap fan bearings inside a hot chamber, etc are all obvious issues to an engineer but not the average consumer.
At this stage of the evolution of the 3D printing environment, the current crop of dryers are selling because there’s no reasonable alternative, so people are forced to DIY a solution. For some what’s available is good enough and dirt cheap. For others, such as myself, in a hot and humid environment year round, DIY is the only way to go right now.
I hadn’t realized that activated alumina was available in bulk at such low prices. Around $100 for 50 pounds of nice round pellets:
and around $150-$200 for 55 pounds of silica gel (same website).
I don’t have a firm grasp yet on how they truly compare, but I can perhaps imagine how given the seemingly low efficacy of silica gel at low RH, maybe it would make more sense to do refrigerated dehumidification for the first stage (yielding a result similar to silica gel desiccation?) and then moving on to a better desiccant for a second stage to drive the lowered RH a lot lower. It would maybe save you the separate step of having to regenerate silica gel at a later time. Surely this must be adequately explained in a good tutorial somewhere without us needing to empirically re-discover the knowledge all over again from scratch. Yet, it seems surprisingly elusive. Obviously, I haven’t found the right place to look yet.
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Shipment cost for the 50# of activated alumina would be $60. So for about the same total cost, which would be better: 50# of activated alumina or 5# of drierite? I’m guessing the 50# would do a lot more drying? Or is it a speed issue? Supposedly both can dry “up to” -100F dewpount, but I’m guessing the 50# would be sure to have ample capacity to do the drying in one pass? Or could handle all moisture: ejected moisture as well as all moisture in whatever makeup air.
What’s the figure of merit that would indicate how fast a desiccant will uptake moisture? All else being equal, more faster is more better.
Ah, yes, shipping costs. I pay for shipping twice on routine goods and for larger things, where larger means over 2 cu ft or over 50lbs, I also pay customs duty and possibly even a customs broker’s fee. All US goods go to my freight forwarder in Florida that puts things on a ship so I get my goods 2 to 3 weeks after they received it for me. Ocean freight is expensive.
Recently, as part of an Amazon shipment, I received a small $8 box of coffee filters that was shipped in its own box, so retrieving that box cost me an additional $15. Amazon does this all the time. It was part of a much larger order that I hoped would sequester those filters in another box of goods, but no such luck.
That bag of beads would probably cost me $150 above what I paid for the product from the supplier.
That’s essentially what I’m working on. Pump > silica gel > Drierite > filament dryer
The silica gel is to precondition the air and remove whatever water it can before the Drierite gets it to help the Drierite last longer. The silica gel is easier to regenerate and at lower temperature so I’m all for letting it kock down excess humidity. The Drierite then takes out remaining moisture to actually create the “dry” air.
Oops - missed that was alumina. What I wrote doesn’t apply…
A bit late for me to take notice that the molecular sieve brand that amazon sells has a regeneration temperature of 550C (1020F) for the desiccant. I don’t own an oven which can even heat up that high. I’ve read that some people regenerate it in a microwave oven, but apparently that comes with a risk of progressively damaging it.
In contrast, Drierrite regeneration temperature is 220C for roughly1 to 2 hours. “Activated alumina” desiccant is at a similar order of magnitude. Hence, I’ll be giving these a try first.
I’ve read that one of the selling points for a molecular sieve is that it can both adsorb water and survive direct contact with liquid water, whereas, for example, silica gel will more or less explode/shatter if it directly touches liquid water. Thus, the role of molecular sieves in some systems is to protect silica gel from direct contact with water by inserting a pre-stage column of molecular sieve in front of a colummn of silica gel…
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Just started with the same issues, wet spring in Minnesota I think
I always had problems with my open printer between winter and spring or summer and vice versa. Especially when it came to cooling and ambient temperature during printing.
I went to buy a bag of the stuff at Lowes yesterday, and it turns out that calling it “pelletized” is a wild exaggeration. Those photos must have been close-ups, because the particle size was almost like sand. Useless for present purposes.
I’ve done more reading since I posted that question, and based on what degrades Drierite, I think we can guess what makes it different from the raw material that company may dig out of the ground. First, what degrades it? 1. Dust, 2. whatever gases and liquids that might get trapped inside the pores of those pebbles.
So… when it’s dug out of the ground, it will already be compromised in those ways.
Therefore… I’d wager that company has figured out how to clean those contaminates out of it, thereby establishing a prestine state. Maybe it washes the gravel with a special cleaning solution, then washes that completely out, bakes it bone dry, and finally blows away whatever dust. It’s their business, and over time they got good at doing it. i.e. By whatever means (probably tightly guarded as trade secrets) they converted gourmet dirt into high performance desiccant and then priced it according to all the goodness that it can do.
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I’ve seen a couple projects on makerworld that look like you could enclose your ams or if you want to go all out you could design your own another option could be just getting an enclosure exclusively for the ams and a filament dryer for any filaments that you aren’t actively using
@IslandBill are you in Puerto Rico by any chance?
And maybe this will help: "Arid Air" Air Dryer to Enhance Filament Drying by MZip - MakerWorld
Personally I’m just keep been keeping everything in cereal boxes with a bunch of desiccant usually activated alumina or molecular sieves.
Interesting discussion here and probably late to the party! I still wanted to add some things that I did not see mentioned:
There is no disadvantage on having your filament ‘too dry’. Brittleness (chain scission) is caused by too much moisture in the filament while hot, which is why you should not heat eg. PET(G) above 70ish degrees (Celsius) if it contains any moisture.
I also saw that Stephan from CNCkitchen upgraded his AMS with a solid state dehumidifier, which I am considering on using in my dry box 
Interestingly, he noticed that his filament was actually drying at room temperature in the box with that thing. Without heat.
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Yeah, this is because “that thing” transfers the humidity continuously out of the AMS. But it dries the filament more slowly than a heated filament dryer. To get the moisture out of the filament faster then it is useful to heat up the air. That’s the physics behind both ways.
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