@MZip OK, I’ll buy that. Attempting to summarize: it’s both low RH and heat (as well as dwell time) which drive the drying process, not just heat causing low RH with only just low RH and dwell time driving it. Seems as though with this configuration, heat is fairly easy to generate, so do the maximum that doesn’t destroy the filament, since it’s easy. If you can somehow dry the air before heating it, then RH should be even lower, and that too should push the filament even drier (or, at least faster). Is that a fair summary? In none of the consumer grade filament dryers have I seen an attempt to dry in the intake/make-up air prior to heating it, by, for example, running it through a desiccant column. Would doing that ultimately result in drier filament, or merely the same dryness but faster at getting there? I’m guessing the former rather than only the latter, but… by how much? i.e. how to decide whether that extra step is worth it? Seems like the consumer filament dryers all decided it wasn’t worth it.
Edit: on the other hand, if you have time to burn, then from what you all are saying, you can trade-off heat for longer dwell time (though, in doing so, you give up the lower RH that would have come from the higher heat). I guess for me it’s moot, as I want the most dry as quickly as possible, especially given that (especially compared to everything else), heat is so easily generated. i.e. it’s cheap, so why skimp on it.
I think you got it. Heat by itself reduces RH and that helps shift equilibrium to water leaving the filament. But heat also provides the energy needed to break water free of the surface where it can be removed so heat helps a couple of ways. Think hair dryers and how slow hair dries without heat.
And absolutely - if the air entering a dryer was already dry, it would be more effective at drying. Only thing is how to do that. You can use desiccant but it needs to be active to work, but pulling air through an active desiccant pack would reduce RH going in and help dry the filament even more. But “wet”desiccant can also source water if the air is dry enough and even raise the RH so have to watch for that.
I’d bet they want to balance cost and complexity. Some would likely never change the desiccant or regenerate it and that feature would be a liability for them. But absolutely - if you can reduce the makeup air’s RH going into a dryer, you’ll dry filament faster and deeper than without. In a way it’s why these “dryers” that don’t exchange the hot humid air in them for fresh “dry” air from outside are so confusing. They will actually slow down drying and can probably even make things worse by having the heat and humidity drive moisture deeper into the core of the filament since near the surface will tend to be where most water accumulates in in filament that has absorbed water. The total amount of water doesn’t really change but you help distribute it deeper into the filament.
I had to re-read and parse that passage more carefully, but, aha, it confirms what I had originally thought. If drying to an asymptote of no more loss of mass, a lower drying temperature is not going to match the higher drying temperature in drying effectiveness. Past that point of asymptoting, you can continue drying at that lower temperature for as long as you want, and it just won’t matter: the higher temperature, if allowed to dry to its asymptote, will have dried the filament better, and the lower temp drying will never catch up to it.
Thanks for the clarification! There are so many conflicting opinions on such a seemingly simple thing that it’s nice to finally get to the bottom of it. This saves me from having to run a bunch of experiments to decide it for myself empirically.
I know the thread has gone a couple directions but a couple relevant thoughts:
I wish I’d read this before buying a Sunlu S2 Plus. I used a datalogging temperature/humidity/CO2 sensor to confirm that it’s garbage - never made it above 37C when it was set to, and reporting, 50C. And it took 3 hours to get there. Back to Amazon it goes.
One thing to consider as an alternative to hygrometers is humidity indicator strips. They’re only good to the nearest 10% but for me for filament storage, knowing I’m below 20% is I think good enough. I got some from Dry & Dry which also sell giant silica gel packets that have saturation-indicating color beads.
Kudos to you for doing that. If more folks would just not let these companies get away with selling product that doesn’t meet their own claims, then maybe they would be pulled from the market.
On the larger subject of your testing methodology. This was the intent of this thread and thank you for adding your contribution to the body of knowledge.
On the subject of moisture cards. They absolutely have their place. Hygrometers are great for revealing near-real-time moisture but that doesn’t measure moisture over time, does it? And if you think about it, that’s what we care about with filament, not what is the humidity now but what was the spool exposed to. For that, a moisture indicator card is absolutely the right tool.
I’m leaving this link for those folks who may visit this thread in the future or for those folks who may not be familiar with what a moisture indicator card is. It doesn’t matter which one one uses, just that one does. https://www.amazon.com/s?k=mositure+indicator+card
TIP: How many of you know that just like silica gel, a moisture indicator card can be restored by placing it in a filament dryer or in an oven or microwave? Just remove it once the color changes back.
I’m curious where you put your sensor. Did you have a filament spool to approximate in-use conditions? There won’t be a lot of circulation in the S2 even with that fan. The heating plates are in the way. Or, was a door prop used? I’d guess no but wanted to be sure.
In the testing I did with an S2, if a spool was in it or not made a big difference to my tests because of the large mixing volume not having a spool of filament in there created. I was looking at humidity and not evenness of heating, but filament in there or not made a big difference in how well it operates.
Hot and cold spots are an issue in consumer filament dryers. There’s been a number of posts here and at least one recent one where people warp their printed spools even though the temperature should be below softening.
It actually fit snugly next to a spool, which meant I could have it located above the spool’s center where I was most worried about the temperature (since I assume the dryer’s sensor is somewhere near the bottom). No door prop.
There might be an argument that because my sensor’s housing was contacting the dryer’s internal wall, which is cooler than the airspace, it was getting cooled down a bit by that. But I just don’t see that accounting for a 13C difference. Here is the specific sensor I used: Aranet and I had it with screen facing outwards so the sampling vents were right against the spool.
I’ve also found you can burn silica gel in microwaves, especially smaller packs but I’ve even burned 500g packs using defrost. I plan to use a toaster oven next for both silica gel and filament drying. Silica gel will release moisture above 130F / 55C and I’m sure it’s safe to take up near boiling. I just repeatedly weigh it to see how close to original weight it is to know when it’s done.
There probably is a small hole or grill on the back of the hygrometer which is where it samples the air for temperature and humidity. If the snug fit caused that hole to be occluded by the spool or by the filament dryer housing depending how it was oriented, that could really skew the results.
Many people think the cheap hygrometers are junk and that’s probably true for some. However, I bought a bunch of the little round ones to use for filament storage and found them to agree very will with each other - if - I was careful to not block that port in any way, and I could get them to react and settle faster if I actually directed air into that port on a project I created.
The two pockets are for those round hygrometers. The odd-shaped ports with bars across the channels are to block airflow a little to cause some to divert into the hygrometers. Response is faster and just flowing air through the assembly they read almost identically and respond quickly.
The hygrometers respond relatively slowly to humidity and take a while for readings to reach their final value if you don’t do that. They will take even longer to respond if the measuring port is blocked in some way.
This can easily happen with high power microwave ovens. All the ones I’ve ever seen do is duty cycle the full power microwaves which with small amounts of materials basically concentrates a kilowatt or so of energy even if only for a few seconds at a time.
The best way to be gentler on beads in a microwave is give the energy more places to go by putting something else in the microwave with the beads. For food, a glass of water can really help reduce the power levels in smaller amounts of food. (Ever see a small amount of some meats throw an arc?)
For drying beads water isn’t really the best sink but you can also buy special plastic-encased hot packs that you can heat in the microwave with beads. They give a place for the energy to go so the beads don’t see the full power output while not adding moisture to the microwave while beads are in it.
Obviously the hot packs have to be microwave compatible (kind of how most get heated so most are but verify if you do this) and you don’t want to overheat them by using them too long during a dry.
The Black ones seems to work great, I have had trouble with the White ones though. Which seems weird because it’s only a different color, but the White ones are bad enough that I will never buy them again.
Unfortunately it can. The minimum reading in the image doesn’t count since it autoselected a pixel not on the Sunlu. The other measurements are on the exterior of my Sunlu instead of the inside, but you can actually see the uneven temperature distribution in the IR image. I think that’s why they added the fan in the S2+.
My sensor was placed between the spool and the UX panel side of the device, just above the top of the LCD screen - about where the coldest spot is in your thermal image. So there would have been the extra insulation of the multiple housing walls and cavity, and it would have moved the spool away from where the sensors are, creating more free space for air circulation near that side.
For what it’s worth, of the three spools I put in there that were each about 800g gross, it only removed 1g of water. Of course I don’t know how damp the spools were before I put them in.
There’s an easy way to get an idea how much moisture is in any spool of filament. It’s not a direct measure of water content but is indirect. Just put a spool and a hygrometer in an impervious container and seal it. No desiccant. I’ve used poly cereal boxes and gallon ziplock bags. Ziplock bags let water through them but the spool will overwhelm the virtual water leak.
Give it 10-12 hours and read the hygrometer. I haven’t gotten many to try this so there’s not a body of data to guide you but what I’ve found is filament out of the shipping bag can show 20-40% RH numbers. After I dry mine it buries the hygrometers at 10% but since that’s as low as they can read I don’t know what the final numbers are. With experience you’ll know what is pass and what is fail.
The reason I don’t have better numbers to help is the way I dry my filament really dries it. It’s why it keeps my humidity low in the AMS and why the filament pulls my storage containers below 10% humidity. I don’t have humidity issues now. Not all prints are perfect but I don’t have moisture issues at all with PLA, ASA, and PETG HF. But I’m probably well below any transitions from good to bad with filament moisture.
I bought Booth for Testing the Spacepi Double and the sunlu S2.
I definetly go with the space in Performance and drying. IT goes mich better brings good airflow and drys very Well.
But Theres one issue. The bearings are that strong that i cant Print flexibles Out of IT.
(TPU80A)
Thanks for sharing that data. That’s pretty eye-opening. I like that idea, it also gives me an idea for performing checks of new spools of filament going forward.
It’s a neat trick and really works well. Why it works is desiccants and desiccant-like materials will pick up certain amounts of water at various humidities so you can generate monotonic curves of moisture content vs humidity. The graph is desiccants but filament will behave similarly.
These are curves but the shapes don’t really matter. What matters is there’s a particular moisture content at one humidity and another moisture content at another. That’s how humidity in a sealed box or bag of filament can be used to get a handle on moisture content. Not a moisture content value, but there will be a value. When we find the go/no-go humidity, we’ve found the go/no-go humidity for that filament moisture content even not knowing the moisture content.
All that said, different manufacturers and colors could have different go/no-go humidities but for a particular type like PLA or whatever, it’s just a guess but I’d bet they are really close. Like I said somewhere here, it’s looking like drying to 24% RH at 55C is maybe enough for PLA while 20% seems necessary for PETG HF (preliminary data).
I’m in the market for another tossing up between the Sunlu S4 and Space Pi double filament version. I’ve had the Eibos Polyphemus but it didn’t rotate my spools as advetised, the rollers just slipped.
Just how bad is the touch screen on the Space Pi? I’ve watched some videos and it looks like pressing a button once can make it register 2 or 3 times - this seems super annoying! (One video I watched was by BV3D, the dude’s pressing the buttons and you can see several times on the video that it’s glitching out, but he didn’t mention the issue once - only positives to say - what a total shill.)
That’s exactly what mine does. It not only doesn’t register properly but when it does, it picks up 2 or 3 clicks. It is to the point that I am ready to see if I can get it repair under warranty. That touch screen is a resistive touch screen, the kind they used back in 1995, it’s a total sh!t-show as far as the wrong technology. Even a Raspberry PI color display has Capacitive Touch. The Sunlu wasn’t much better, they use exactly the same technology. I’m pretty sure that both those designs came out of the same company. There are too many similarities.
