No worries. Thanks for blogging your progress. It was fun to follow your project’s evolution. I’m glad to hear you achieved what you wanted to.
2 Likes
It actually incorporates ideas from a number of people yourself included. Not all my idea by any means.
It’s on spool 8 right now with output still pegged with a display of 10%. Haven’t gone through a regeneration yet to know how that goes but the discoloration in the pellets from increasing water content doesn’t appear to be spreading while I have left it sit overnight. It will, but the rate of spread seems low compared to the increase in coloration from running it. This is good but I still expect if it sits unused for too long the water content will spread out and lead to breakthrough right off the bat when fired up again. Drierite or other chemical reaction desiccants likely won’t do this so an advantage if you want to go lower.
BTW, one last thing:
I have a number of these inexpensive bluetooth TH sensors, such as this one:
Of relevance to you, they cover the full humidity range of 0% to 99% (not 10% and up). They come with bluetooth and you can monitor wirelessly from your phone. So, for $2.19, you get more capability than you typically get with a typical low end TH sensors of the kind you already know.
1 Like
I’m a bit suspicious of that 0% bottom end especially at that price given what Olias found that pretty much all the humidity measurement devices use the same sensor. Electronics do come in the same packages but different ratings so maybe it is one rated down to (near) 0% but I searched on Amazon for it (didn’t find it yet).
Did some digging and found this - might not be uncommon or that expensive to measure that low. Some sensors can measure to a -100C dew point.
Maybe future expansion? It’s definitely something to consider since right now I’m sort of blind to any changes until they get big enough.
On the 10th spool now and exit air still has the exit hygrometer pegged at 10% RH. There’s a dark color growing into the desiccant as the indicator is changing color where the air enters the reservoir but no obvious changes to drying filament yet. Whatever the output air RH is it’s still well below the 19% RH I’ve been drying spools to. In general, each spool that I had in plastic bags in plastic tubs has given up 2 grams or more of water. New spools taken out of their shipping bags also give up water but a little less.
I don’t know how many more spools it will dry before output RH starts increasing but for a wild a** guess, I’m thinking it’s going to be 20-30 spools judging by the indicator at 10 spools. All the color change is still low in the reservoir so there is lots of silica gel above the wetter area to polish the humidity down. There has got to be breakthrough but it doesn’t seem to matter for all practical purposes.
I’m really happy with how well this dries filament. All my testing until yesterday has been with storms and rain moving through occasionally and humidities ranging from 40 to over 60% RH. @IslandBill’s suggestion of an aquarium pump was brilliant and does double duty pushing dry air into filament dryers and displacing the moist air.
There’s a dead volume issue in the custom base for the Sunlu S2 but that will get fixed today. The biggest issue with this is complexity to build. I’ve been using matte PLA to build the base with but it leaks air like a sieve which causes big problems if not dealt with. It’s easy to fix by painting the model inside and out with superglue to seal it up. Not tough but undesirable. Regular PLA may seal better but might not have superglue seal it as well. The hygrometers need pigtails soldered to the battery terminals. The hygrometers and the reservoir lid need careful applications of silicone seal when those get seated. It’s a fairly complex build and I don’t know any good ways to simplify it beyond where it is now.
I’ll post the model for the dryer and Sunlu base soon.
The stock Sunlu base can also be modified to accept dry air. Some advantages to that since that won’t add dead volume below the filament drying chamber.
Here’s what the reservoir looks like at 10 spools dried. The indicator color change is visible to the eye to about the yellow line area. It looks like reservoir capacity is much bigger than I had planned for because the silica is trapping more water right at the entrance than I thought it would. This is why I now think it may dry 20-30 spools before needing to be regenerated.
1 Like
OK, just for you, I put mine under the microscope and got the part number:
I can’t promise whether you would get the same. I guess that’s between you and the seller. Looking at the PCB, it has traces to accept 3 different sets of landing pads. My guess is they slot in whatever jellybean sensor they can find the cheapest and still meet whatever the seller’s advertised specs are.
If you don’t care about the LCD, then I’d recommend you’d get the bluetooth/zigbee version that takes 2x AAA’s and gives a minimum of 500 days runtime. They’re even cheaper! These CR2032 sensors will discharge faster than that. Maybe 6 months. Probably less if powered by the CR2032 battery that comes with it. If you like the LCD, though, some people on the forum here wire it to a battery with more mah’s. Example:
https://makerworld.com/en/models/376261#profileId-276224
In your case, I get the sense this is probably all moot anyway, since it exceeds what you want/need and already have, but for the bigger hive mind, there it is.
3 Likes
That’s a nice chip. Factory calibrated and low power. And they do say 0-100% but also 3% accuracy so might not quite go to 0 but it would get a lot closer than the hygrometers I’m using. Needs a microcontroller and separate display but would allow a whole new level of dryer that even makes decisions and could power itself off. Lots of possibilities. It actually would allow a more sophisticated design and even easier build except for the electronics and programming to talk to them and output values.
So worthy but it would take a clean sheet of paper redesign because it would change a lot and need an electronics bay, display, etc. and it adds people needing to sort how to program microcontrollers and more soldering which as simple as it is is beyond a lot of people.
But it is a cool chip and does show even more possibilities. I’m way behind on other stuff now so I can’t take it on but it could be a top dog air dryer and make it easier to use with the very hygroscopic filament types.
On this dryer, though, I’m printing what I believe will be the final version now, will build it and take photos, and then post it if anyone else is looking for an air dryer. It should be even better than the one I’m running now to get performance numbers and will then do final things with the replacement Sunlu S2 base and get that posted too.
2 Likes
Spool 13 is in the barrel now with output hygrometer still reading 10% RH. The photo is from a few minutes ago. The dark indicator region is growing in and it feels like drying is slowing just a little as time to 19% has gotten just slightly longer. Could also be these last couple of spools are wetter but they were stored the same as other rolls. Drying slowing slightly is what I would expect though as the desiccant picks up water. If this trend holds it might not get to 30 spools dried on a single charge of silica gel but 20 still seems well in reach. Time will tell.
I just set the reservoir lid in the 2nd prototype air dryer base and will have it built today. Overnight cure and I can leak test and check output pressure tomorrow.
Here’s the indicating silica gel in the 1st prototype a few minutes ago while supplying air for the 13th spool drying in the Sunlu. Posting a photo with a flashlight helper to show the desiccant color better.
1 Like
On spool 14 now still with 10% exit humidity. It’s humming along (literally). I’m going to run out of spools to dry in 8 more rolls but can just let it run and keep track of the time. There’s nothing that says the dryer has to be on or have filament in it and I’ve had the Sunlu time out and turn off a few times anyway. The dry air still flowing in protects the filament (if there is filament).
Just pressure tested the new print where I tried more walls and layers but it still leaks air. Not as much as the last one before painting with superglue, but it still leaks so looks like painting with superglue stays in the build instructions.
It could be some changes to other print parameters or type of filament might make it air tight(er) but others can experiment with that if they are so inclined. With 4 walls and 4 floor and ceiling layers it’s almost 400g of filament and an almost 10 hour print per experiment.
If so inclined, you may want to try this:
I would think that if it can hold fuel, then surely it can hold air.
If not that, there’s a couple of products I only just recenty learned about which are no doubt locally available to you:
bondo plastic metal
and
bondo glazing
I learned about it from this guy:
Don’t worry. Despite appearances, it’s not some kind of S&M contraption. 
That said, I’m about to apply a SprayMax 2K primer filler over a 3D printer project for outdoors. At least in my experience, a 2K beats a 1K every time, hands down. SprayMax has made it stupid simple to prepare it. You smash a button on the bottom of the can, which cracks a capsule inside the can so that the precisely measured two components can mix when you then shake it. Then it’s ready to go. Easy peasy. Dry time and cure time are in minutes. Pot life is about 2 days, after which it’s no good anymore. Of course, always refer to the can instructions or the latest TDS to confirm such info.
Also, it goes without saying that proper and appropriate PPE is a must. I know you know that, but for the benefit of anyone else who may not know, I reiterate. I recently aquired a remote air respirator, which feeds fresh air from 50 feet away, so in that regard, it’s the gold standard. No need to judge whether your filter cartridges are appropriate to the task, which is all but impossible for most people to evaluate. Which brings me to an example reason for owning such things as a PPE:
Raptor liner is probably the ultimate. If that didn’t seal your project, probably nothing would. Water proof. Moisture proof. Vapor proof. Tough as nails. Same 2K delivery mechanism as spraymax, so very easy to mix and apply. If it were me, I’d skip the windup and just reach for this, knowing that it would be a once-and-done thing.
1 Like
Not too sure about the internal design, but it looks as if the plastic tubes go into a 3d printed container with the tube containing the silica gel, and the indicators. I expect most of the 3d printed parts could be eliminated in the air path. It depends what you have to hand, or are prepared to purchase/fabricate. Air won’t leak through 3d prints, if there are no 3d prints. 
Standard plumbing fittings/solvent weld, even copper pipe and fittings, do not leak air if properly fitted.
If the bulk of the print is PLA, then ethyl acetate can be used as a solvent, or smoothing, etc. Not expensive from Amazon for half a litre.
2 Likes
My test bed was closer to what you describe. I 3D printed to house/plumb the hygrometers and just enclose everything. Dead volume is important to minimize but so is back pressure which is why the interior plumbing in the 3D print. Sure, you could omit the hygrometers but that information helps keep tabs on drying to know it’s working properly. The indicating silica gel is an at a glance way to see how it’s doing but doesn’t tell you about breakthrough if you are running too high of flow. The exit hygrometer will.
Sure, there’s lots of ways to do this and I’m sure there are better ways. All it is is an air dryer and an aquarium pump. I’ve said that numerous times in this thread. I’ve gotten what I wanted out of this and it’s just about done with spool #15. Still just cranking away.
I encourage anyone with other ideas to try them. The minimal design would just be a pump, tubing, a container of desiccant where you have an inlet and outlet, and some more tubing. Easy.
But I didn’t want parts dangling about or rolling off a table. I wanted a contained system. And I wanted to know inlet and outlet humidities. I had thought it wouldn’t be too difficult to make it air tight and the last version almost was but it started building in stresses that were warping the base a little. Painting with something to seal it air tight is a pain but mine’s air tight now and it wasn’t hard. The 3D print was to make it where you didn’t have to go buy PVC or copper fittings, braze copper, or solvent weld, etc. Had I been able to make it air tight it would have been even better but I have put too much time into this already.
You should try your ideas out though. They have merit and you could be onto something.
1 Like
The beauty of it being a positive pressure design is that even with the air leaks, it still works anyway. i.e. it’s robust, provided the leaks aren’t too severe. Without air leaks It would work longer before having to change desiccant, but even with them @Mzip is able to process a surprising number of spools. So, from that perspective, no big deal.
Nonetheless, you’re point is valid. If it were a closed loop design, as I was and still am considering, then air leaks would potentially be a problem.
But, to your point, if you were to go totally minimal, it wouldn’t need any printed parts at all. Consider:
Hook the pump to the inlet with tubing, then tubing from the outlet to the filament dryer. Done.
In that instance, the cost would be higher, and it loses the RH monitoring, and it loses the visual beauty of @MZip 's design, but in return it’s over and done probably pretty quickly, and maybe without leaks.
I hope a lot of people build their own variants and post them. There’s a lot of ways this could be built. Or just build @MZip 's version, since it’s proven. Or just do the minimum to get up and running right away and then maybe enhance it if and when time permits to monitor RH or weight or regulate airflow more tightly or switch to closed loop or whatever cool improvement you can dream up.
One of the big unknowns at the beginning was how much air pressure would be needed to push air through the desiccant column. Thanks to @MZip , we now know that it’s not much, and that an aquarium pump is enough to do it. That’s also good in another way: less pressure means less loss from leaks.
1 Like
Which air pump are you using? It sounds like to get adequate pressure, you also need to go high flow? Is that right? If so, have you found one that allows lower flow but still adequate pressure?
1 Like
I’m using this one. Turns out the metal outlet tube is a pretty severe flow restrictor so I took it out and a rubber tube connector, and connected directly to the actual pump inside the outer housing. The aquarium tubing it comes with fits the internal pump and the hole/mount for the flow restrictor.
KEDSUM Quietest Aquarium Air Pump, Adjustable Oxygen Aerator Pump with One Outlet / Amazon - ASIN B08FJ1HRTP - $21
There is an electronic throttle that controls the pump pressure/flow and those go hand in hand if that’s what you’re asking though that flow restrictor may have had something to do with that. I didn’t test flow pressure or volume except for the whole system without the restrictor since I figured the beads and air passages would have their own flow restrictions.
The pump itself would probably have highest flow at lowest backpressure and hit highest pressure at stopped or low flow maybe. There could be some funky working curve that changes that, though. I just don’t know those bits but a proper treatment would have looked into it if flow was more important “than that ought to do it.” It’s actually a pretty complicated problem. Somebody could probably go to town doing the fluid dynamics calculations to start with knowing optimum flow into the filament dryer and work backwards from that. I don’t have a clue how to do that. 
Added - I’ve been running at a pump output setting (about 3/4) that got me 5 1/2” water column pressure with a fair flow (no idea the numbers but the bubbles gave a pretty good feel for the flow). The glass I was using wasn’t tall enough to go deep enough to stop the flow to know the pressure it could hit. But it’s a compromise. You don’t want to push so much air that you don’t hit good temperatures across the filament dryer while balancing with flushing the moist air out. There’s probably an optimum.
The other thing is I found an online calculator that was eye opening and looked like maybe all you really need is an aquarium pump and don’t even need desiccant. Try it yourself. It tells you the RH when you heat or cool air from a starting RH and temperature. You can see what happens when you heat room air to filament drying temperature.
So I’ve got a spool drying using just the aquarium pump with no desiccant column. It’s 5 hours in and only lost a hair over 1g so is lagging how other spools behaved but seems to be tracking the drying session where the filament dryer door was propped open. I’ll continue the dry tomorrow. Unfortunately its weight has to level off and then I have to feed it dry air and see if weight continues down or not to answer this one.
It’s the usual problem: the thing I want isn’t what’s readily available. It’s understandable that the market wants a high flow air compressor, not a low flow one. So, they’re equipped with motors that produce high torque at high speed, but low torque at low speed. In contrast, I want adequate pressure, at low flow, and I’m not finding it on amazon.
So, I just now ordered a couple of DC powered units, and I may try running them on PWM to see if either one will do the business at pushing air at a low flow through the drierite column I posted just above. The good news is that column wasn’t available on Amazon when we first posted about drierite, and now it is. Before, there was only the over-priced $200 listing, IIRC.
Also, my prior assumptions about drierite desiccant being expensive were wrong, because they were informed by the pricing on amazon, which is high. I only just today noticed that the pricing looks quite reasonable if one were to order from drierite directly. Well, MSRP at least. I haven’t checked shipping.
What are you planning to do with your drierite? You had it in an earlier version, but you apparently dropped it in your later versions.
I too may end up putting silica gel ahead of the drierite, if only because there are some options for fast recharge on silica gel, which would get me more mileage on the drierite before having to dump it out and recharge it and then repack it.
Also, I think I’ll put at least a little bit of air filter ahead of the drierite, since dust and contamination is known to degrade it. I suppose the packing in the column might serve that purpose, but I’d just as soon keep the column components as prestine as possible. Aquarium in-line air filters are cheap.
Gosh, creeping elegance is already starting to insert itself. I’m going to keep it bare-minimum on the first pass until I can confirm how well it works. Thanks to you, though, the risk sounds pretty well removed already. By that I mean: it seems reasonable to expect positive results that justify the effort.
You’ve lost me, there. If as the chart shows, you don’t need desiccant, then why do you need to pump in ambient air? Is it to force out the heated, moisture laden air? It may work better, instead of a constant air change, you let the drier accumulate hot moist air, then purge it, and wait for it to accumulate again, then purge. For the rubbish solvol unit , I made my own controller, basically hygrometer and thermometer relay units , I found that opening the lid to let the moist air out, then closing, reduced the humidity, (but that was for the air). Adding silica gel definitely sped up the process.
I do indeed have some spare Drierite. It’s all dry - even the material that is in the test stand. Don’t know what I’ll do with it, though.
Drierite will polish the air way dry but it takes high temperatures to regenerate it. If you go the Drierite route to get the really dry air, I’d recommend putting silica gel in front of it to grab the lion’s share of the water since it’s easy to regenerate. It’ll keep your Drierite active much longer but it looked like the Drierite was still picking up a little water that the silica gel was letting through. When I was considering Drierite I was also looking at a small Drierite column and a big silica gel column for that reason. At low flows it shouldn’t need to be big but YMMV.
I may not be understanding about the high pressure but you can always throttle after an air dryer but any leaks will be more pronounced. In my case, throttling at the pump is working fine but I’d bet I’ve got lower backpressure from my column. Welcome to the balancing act. 
Pushing out moist air is absolutely a function of the pumping and it’s not a straightforward issue. Water will leave filament faster if the air is dryer. Letting moisture build up between purges may more effectively purge out the moisture (or it may not) but it leaves filament sitting in more moist air longer. This is why I said somebody with the skills could possibly determine the optimum flow rate for filament drying that balances heat loss with sweeping out moisture, etc, and then building a system that can do that.
Long time ago in chemistry lab I had a teacher who impressed on us how to properly rinse glassware. It’s an easy thing to calculate but for rinsing, batch rinsing was better but a water tap isn’t low flow and you don’t have to wait to rinse. Key to proper rinsing also was emptying residual rinse water from the glassware before adding fresh.
It’s similar but in practical terms it’s a lot easier to just let the air flow. A complicating factor is the filament is releasing water constantly in the chamber.
You also have some dryers with fans inside that make the filament dryer a big dead air space that averages out humidity and moisture and slows the exchange. But without that there will be some stratification and different filament environments from top to bottom.
To actually do the topic justice there is a lot to consider. Pair that with different filament dryer designs and there’s even more to consider.
It’s all hand waving though. The best thing to do is set up a test fixture and try out your ideas yourself. You’ll get a whole new appreciation for all the things that go into this and unless you have computational fluid dynamics skills, real world testing is all we’ve got.
What I see is an initial broad peak in humidity in the drying chamber when I put in a spool as the filament heats up it starts releasing water. Humidity rises in the chamber and a higher flow rate would help sweep out that extra moisture. But to do the equivalent with a dry air source isn’t straightforward. Maybe cobble in a servo and microcontroller to open and close the door to let out moist air, but unless you’re only doing it for yourself, now you are adding complexity and hardware, making it specific to some filament dryers, and asking more skills of those who might build it.
There’s a big difference between making something you can use and making something others can use. My goal was something anyone could use but even at that there are challenges if people have never soldered or whatever. But anything to do batch or other strategies starts taking valves, a microcontroller, programming, and so on. My design is as simple as I know how to get it and still do what I want it to do.
There are absolutely tradeoffs and that’s part of the design process. You have to decide what is important and what is nice but maybe not worth the complexity it would require. Like I said, give your design a try and let us know how it goes.
Also, look close at silica gel in a filament dryer. Silica gel regenerates at low temperature - not far away from filament drying temperature. At drying temperature, the silica gel will turn into a water source if it has absorbed much water either during other spool dryings or just sitting in a leaky dryer. The reason drying air before it goes to the dryer works is because drying the air happens at room temperature. Using a desiccant like silica gel in a filament dryer may work at first but will stop working and will even work against you if you don’t change it out when it picks up moisture.