Hey @Olias - a stable base version. Who needs brim when you have a big puddle of plastic? 
. 3mf now has 4 bases in it - with and without a port for a temperature/RH meter and with and without the stable base. Was trivial to add but definitely see the utility! Just finished printing an updated fan mount so can do the assembly and set it on a stable base with RH port when that finishes. I’ll be testing this evening…
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I can already tell this is going to work - at least with ambient room air and just the fan and holy throttle plate 
I get a good (but probably too good) stream of air out the vent holes with the lid closed. Printing the stable base now so have to wait to really test until that is done but with a base I should be able to regulate the flow out of the filament holes by using the swivel flap to regulate air into the base.
I used silicone seal to secure the fan mount. It has two locating pegs that can be expanded with m3 screws to tighten it up even more but I don’t think they are necessary. Just a little dollop of silicone in the holes should lock the fan mount in. I ran silicone around the port to seal the sides as well. The base area of the S2 is curved across the base from front to back, but it’s not as pronounced as the side to side curve. So the silicone around the port may be necessary. Not a big gap at the sides but a gap. In the last image the roller is just being used to hold the heater. But so far so good.
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@MZip I’m following your progress with great interest. 
After you get it working to your satisfaction it would be very interesting if you could somehow quantify how much extra moisture your modified S2 is able to extract from a spool of filament as compared to a stock S2.
It may be hard to quantify that since each roll has its own history and starting water content. Best I could do would be to run some rolls bought at the same time from the same lot and color but that might be close enough. I do think comparing how desiccant loses its water should be a fair analog, though.
In doing all this I think the Sunlu is actually a little leaky around its base plate but mine is now sealed. Worse, the fan has turned the base into a sort of pump so it’s hard to say how close I can get now to a stock Sunlu. I should have run tests before I started modding but this was a slippery slope. Before I knew it the feet were off and wires were cut. 
But also, I’d need to do a big filament buy to try to take starting water content out of the mix as much as possible. It’s sounding like a bridge too far, to be honest.
Hopefully these desiccant runs give data that can be compared easily. I’ve run out of time today and silicone is curing. Tomorrow we ride!
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No worries. I especially don’t want to burden you with any requests that don’t align with your own interests. Nonetheless, if you ever did get curious about it, I’d wager you could get a pretty good answer by
- Note the initial weight of a filament spool before attempting to dry it, then
- drying it to asymptote without connecting your desiccant apparatus, then
- weigh it again and record the new weight
- Connect your desiccant apparatus and dry it further until it asymptotes again, then
- record final weight measurement.
Or, maybe there’s a better way. I’m sure you get the gist of it.
I did a variation on this measurement just recently, and the results surprised me. First I dried a spool of ASA at 80C for almost 3 days, measuring its weight beforehand as well as at several points in time along the way, until the weight loss finally did asymptote.
Then I quickly transferred it along with 500g of absolutely brand-new and fresh-from-a-sealed-package dry-and-dry silica gel desiccant into one of those sealed, gasketed cereal storage containers that a lot of people use for storing their filament. If anything, I thought that maybe the filament spool might lose a little more moisture to the desiccant. Well, two weeks later I opened the container to finally use it, and so I weighed it again. It had gained 0.5g of weight. How? From where? Maybe from the desiccant itself? That would be ironic. From the container? Seems unlikely, but I can’t rule it out. Maybe from ambient moisture penetrating through the container? I’m starting to wonder. Fortunately, I was at least able to rule out a measurement error because I have a 1kg calibration weight for calibrating the scale, and when I weighed that on the same scale it showed absolutely no measurable change in weight, and the scale’s resolution goes to 0.01g.
Now it has me wondering if whether I had stored the filament spool like that even longer whether it would have gained even more weight. So, just sayin’ when you start carefully weighing stuff–which takes barely any time at all–you may be surprised at what it turns up.
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My S2’s don’t have the fan, but I’m watching.
I am curious about cardboard spools.
Since my S2’s don’t have a fan, I don’t have a problem with cardboard spools…
But my Creality Space Pi, looks like it went mudding after 2-3 days of running cardboard spools. Cardboard dust all over the inside clear lid.
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All good points and I’ll look into scales. It would just tie everything up nicely and people do use weight as a gauge for moisture.
About the ASA gaining weight in desiccant, I can see it. The ASA is known for being hygroscopic but obviously so is fresh desiccant. It could be that the ASA is a stronger desiccant than the desiccant and took water from it. It’s just a competition for who wants the water more.
What happens is the sites where water sticks have a range of affinities. It’s like those weights that get harder to pull at a tractor pull. The first water is easy to remove and the last water is really hard. It ends up just being a competition for which material has sites left that bind water stronger.
Or maybe the seal wasn’t tight or water diffused through the poly? Weighing the desiccant too would have told if it was gross water infiltration where both absorbed water or if the desiccant gave up water to the ASA in a closed system.
Hard to say for sure but water is really hard to get rid of. I used to work with vacuum systems and we had to pump things down and then heat the heck out of the vacuum chamber to get the water to unstick from very clean and dry looking metal and glass surfaces. To hit low pressures we’d have to pump and bake for hours to days.
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Hey @lion7718 - since yours doesn’t have the fan, have you removed the bottom plate with the feet to see if it still has the port at the bottom of the housing?
If you have the hole and just no fan, it’s a little tougher but your S2 power supply is still probably 24V. (Is it?) Worst case is you power the fan from the power jack but you may even have switched pads on the circuit board that would only run the fan when the dryer is on. I think @Olias figured out how to get to the board but I don’t know if there is provision or not. They may have updated the circuit board when they added the fan. Or maybe they had pads for the fan from day 1?
About cardboard spools, have a look at the spool holder @SimEyeSee posted above. It looks like it might help with cardboard spools. There may be other similar spool holders for the S2.
Cardboard dust could be a bigger issue with this mod though since the air kind of jets into the new base but is blown up by the fan slower to generate the pressure differentials. I think it would tend to concentrate and collect in this base but pop the RH meter out and the whole dryer could be tipped to pour out collected dust? I don’t have experience with it to say. Not sure?
I started it heating with PLA settings and the side port wide open. Ambient humidity is 52% at 24.2C. The meter in the base is showing 41% (room air mixing with dryer internal air) and 29.1C. And the dryer chamber is showing 29% at 55C.
I haven’t timed time to temperature but the wide open side port has to slow that down. I also notice the dryer going into heating not super frequent but more than it seemed before. Need to get numbers on power draw over time to see the impact there.
No desiccant yet. That will be the last part since the desiccant will change as it runs and I only have enough for 2 fills of the Nalgene bottle. But so far it’s behaving proper. The drying curves should be interesting. Still have some more static testing first though.
Edit - with the side vent fully closed, the numbers didn’t really change which makes sense because it’s just air right now. As long as it heats to the same temperature it will fall to the same RH. The base numbers didn’t change either and I thought they would, but that sensor is all the way across the base on the other side of the fan and all the mixing it does, so while the base is still cooler than the dryer, it’s measuring the same with vent open or closed. This implies that the base is losing more heat than the “cold” air entering uses to come up to temperature.
I think it really is working as I hoped. Got more fun stuff for later but now comes the tedious part with desiccant. All the steady state stuff looks great. It does spend more time in heating with air coming in but it still gets to PLA drying temperature. I guess I need to test max temp it can hit with full air and closed. I guess that’s next then…
The base adds more load to the heater. Temps are rising but seem slow. With the side port closed and whatever leaks may be present (hopefully small), it’s taken 6 minutes to get to 64C from 55C with a setpoint of 70C. I may go back and add fences in the base to more or less help contain the hot air or just pull the walls and floor in to minimize volume and maybe pick up more insulation value.
At 17 minutes to hit 68C from 55C with the port closed. I saw the utility for an IR viewer and it is showing hotspots on the base walls where the hot air from above gets ported down into the base. Maybe some insulation attached to the base inside would fix things up. And looking at the walls, the RH/temperature meter set into the base is in a very dead air and cool region compared to the end where the port is. The base itself doesn’t care. I could have mounted it either way but didn’t realize the consequences. The way the fan mount attaches the fan is on the center right looking at the S2 display. The port down into the base is to the left which the way I mounted the base, the outside air port mixing in is on that side. The meter is in dead air. Got to think if that’s good or bad for the purposes of what it measures in each location but location does matter. And it hit 70C at around 29 minutes with the side port closed. Room temp is 24C / 55%RH. RH is 20% in the chamber and 34% in the base / 36.5C.
I opened the side port all the way and temperature in the chamber is dropping a little. Seems to be holding at 67C at the same 70C max temperature setpoint. It can’t hold maximum temperature at maximum port air and the heater is running full time. All this is with the “holy throttle plate” set fully into “closed” position and both filament exit ports open. The maximum temperature in the Sunlu canned routines is 65C and it’s now holding that just fine with the side port fully open. So not perfect like it is but some insulation may help.
Heating to 65C and 20%RH in the drying chamber with 1 desiccant pack with the side port fully open and fully closed. Will rerun with 65C as the target, but this morning just testing without desiccant packs and just air but to 70C, it hit 20%RH in 29 minutes.
With a desiccant pack and the port fully open, time to first heater off cycle was 35 minutes. With port closed, 19 minutes. Makes sense because of the heated air being lost from forced air exchange. It will take longer and more power to heat up to setpoint. Add a full roll of filament and it may be a while.
So far on the humidity curves, port open to ambient air for forced air exchange is lowering RH faster than port closed but not by a whole lot faster. It’s looking like where this will really matter is when the curve slope gets more shallow as it nears asymptote. Right now, port open is 8 minutes faster to 34% chamber humidity than port closed - at 30 minutes into the port closed run so a fair difference. To hit 32%RH, port open took 24 minutes while port closed is at 34 minutes. Difference is growing in. Now a 20 minute advantage to 28%RH for the open port - 30 minutes vs 50.
It’s looking really good at this point. I still need to finish this run, run a duplicate port open run to verify I can trust differences in the numbers, re-run with just air at 65C, and try the desiccant “dry air” feed. Even if that doesn’t work the way I think it will, just a change to this base with the port open is looking like a big benefit.
The port being open with the design as is limits the maximum temperature a little (2C in my test) but some insulation or closing the port a little should get it back capable of hitting 70C in the chamber.
I’ll graph the data when I get the runs all done. I think that will really tell the tale but with a single desiccant pack if the trend holds, it could be cutting drying times significantly just as is. Haven’t explored the other throttle plate or positions, partial side port settings but even this is looking good.
Port closed may or may not accurately simulate an unmodified S2. That stock base plate might let a little air convect. But the way it looked, it wouldn’t really be forced and there is no adjustment. It’s now timewise where I ended the port open test (at 20%RH at 64 minutes but is still showing 26%RH at the same time into the run). Just guesstimating but I bet there’s another hour to get down to 20%RH.
At 2 hours with the side port closed I ended the test. RH in the chamber was 24% and at the slow rate it was going down it could have been another hour or more before it got to 20%. Open port did that in 64 minutes.
But have an issue. The hood on the fan mount is sagging ever so slightly in the heat. It’s the closest to the heater plate. I can either delete it or print it in another plastic that takes higher temperatures. The cooler air from the fan is probably all that’s keeping it from sagging significantly. The fan mount itself is fine. It’s just that hood. From the image, though, it looks pretty effective at blowing air up and around the right side of the chamber.
I would add an Arduino or similar to control the fan, so it’s running for a few seconds every 10 minutes or so.
You only need to change the interior air when it’s moisture level has raised.
This would keep more of the energy inside, the power consumption would be less and the temp will raise faster.
@ElektroQuark - pulsing the fan just a little is going the wrong way and an Arduino is way too much complexity for this. Venting through the filament holes if anything is too restrictive. Running the fan constantly makes it harder to hit maximum temperature but the RH lowers in the chamber much quicker with the fan running than if it ran just a little.
RH fell to 20% in the chamber in 64 minutes with the side port open and just letting the fan rip. With the side port closed the lowest the RH hit was 24% after 3 hours and I stopped the test. The box needs fresh air to chase out the humid air.
The port open / port closed test was very successful and showed the fan constantly pushing out humid air lowered humidity much faster. The heater ran harder with the port open but overall the time it needed to run was probably much shorter.
It’s better if the fan runs constantly by everything I saw yesterday. I do think insulation and/or minimizing the volume of the base chamber would help to minimize heat loss through the base though.
I really think running the fan less won’t provide any advantage. Like I said to Electro, with the side port fully open where air exchanged fastest, RH dropped to 20% RH in 64 minutes. With the side port closed I stopped the test at 3 hours at 24%RH in the drying chamber. Air flow through the chamber helped reduced the humidity much faster.
I’m not following what you are doing with those screen grabs. Maybe an explanation?
Since the setpoint temperature I was testing to was 65C and all runs were hitting that temperature, we should just be able to compare RH values and no need to convert to dew point or actual water content. If the temperatures were all different then I get using dew point but unless I’m missing something, that’s not needed.
The port open/closed tests were to see if there was benefit to forced air exchange. I knew there would be and the test verified it. Port open was significantly faster at lowering RH than port closed.
With air exchange you lose heat in the air you push out, but the base ended up being a heat load I hadn’t considered. Reducing volume in the base and maybe even insulating would probably allow the chamber to hit setpoint faster and waste less energy while drying, but lowering RH faster and drying rolls faster should save energy too.
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OK, that explains it. My post doesn’t apply then, so I’m taking it down.
@NeverDie - I’m not trying to get you to pull it or trying to shout it down. I was just saying I don’t understand. If you feel it was correct, I’d rather you explained it.
Boards are a hard place to navigate. When I write with trying to be accurate and precise it comes off as harsh and I don’t mean that at all. I’m just trying to understand what you were saying in a free exchange. This isn’t my area and only a little connected to parts of my background so my grasp is tenuous.
No, I don’t think you’re harsh at all. My post was based on a mis-reading, that you’ve since clarified, so leaving it up would just muddy the water.
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Printing in a high desert environment probably doesn’t need a dryer when using PLA, PETG etc. Filaments don’t have to be done-dry to print well. One can save the hours drying filaments.
But a dryer should come handy when printing hygroscopic filaments such as PA (nylon).
A fine example of “Civil Discourse.” Kudos to you both for a great example of mature interaction. All too often, such misunderstandings caused by the imperfect world of written communications can devolve into a flame war. I find it a beautiful thing when it ends up in a mature dialogue like this instead. 
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@DWdesigns Except that sometimes you might get even a pla or petg that arrives already soaked, fresh from the box. In that scenario it wont matter if you’re in the high desert or not.
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I’ve had a few times where my AMS humidity has gotten up a little and models have suffered. Plus we’re in monsoon now so humidities are more like the rest of the planet for another month or so. And, as others have said in other threads, even opening a freshly delivered roll of filament is no guarantee the roll won’t be “wet”.
I do need a dryer for more consistent results or rejuvenating stored rolls, etc. And I like how this is performing. I’m printing new parts now to fix the issues I discovered yesterday. It’s quieter, dries faster, and I can’t wait to actually dry filament with it.
But with the issues I’ve seen getting to this point, I think I’m taking this dark for liability reasons. I didn’t realize that Sulu dryers could actually start softening/melting filament at their highest temperature setting and that ability scared me.
The more I thought about it, this mod changes the operation of the dryer in ways that a lawyer would eat for lunch if anyone was to have an issue and sue me. There’s a component (fan) change as well as the heater duty cycle increasing while it’s running. I don’t think it would ever catch fire but who can say this isn’t doing something that could cause one? I don’t think a big disclaimer would protect me either and consulting a lawyer takes it way out of what I’m willing to do about this.