I have just received a SUNLU S2. My wife complained about the fan noise. So I opened it up unscrewed the fan and re-attached it using silicon rubber to mechanically isolate the fan. Now it’s silent. Now I have a question the thermal sensor location. It’s in the bottom of the box near the heating element. I wonder why they couldn’t have located it next to the RH% sensor located in the rear of the electronics at the centre of the spool hub. Seems it would be more accurate and less wiring.
I’ve got an S2 and got some IR images of it running. I can’t speak for Sunlu but the fan seems to create a hot spot near the lower part of the chamber. It’s the outside of the housing but you would want to regulate the hottest part of the dryer to not exceed setpoint temperature by too much somewhere else in the chamber. But can’t say for certain why they do it like that. I didn’t even know the sensors weren’t next to each other.
Those plates in it are the heating elements, though. There’s upper and lower half circles of heaters that surround the filament in regular operation.
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Ah, I see. I guess that explains the reason for the sensor location, yes it is a small black blob thing located in that hotspot at the bottom. The IR camera looks useful! Right now, I have put a glass full of fresh desiccant inside the unit and set it to 64 degrees. I want to see what the lowest RH% is, just to give me a reference point as to what RH% a dry filament should reach. After 2 hours it’s at 18% - so far…
Probably a typo but p (lowercase) is shorthand for negative log. I think you mean RH?
I’m not sure your test will tell you much but who knows? The base of the S2 is really leaky around the edge and I had to silicone mine on to stop that leak. I do my drying different and leaks impact the performance of mine significantly.
The heat helps create a flow from the leaky base up and out the top vents/filament passthroughs. Small flow though and not really enough at the first part of a filament dry when water is coming off the filament wholesale.
The desiccant in the chamber will reduce the humidity but IMHO it’s the wrong place to put desiccant when drying filament. I blow room temperature air through desiccant to dry it and then add the dry air to the filament dryer. As desiccant heats up it holds less water. It can still work as desiccant when heated but not near as well as when cool which also means more frequent changes/regeneration, etc.
Also, during drying there’s a few “stages” of sorts. At first the filament gives off more water than can easily escape the filament dryer. That’s when those door props are effective. They allow more free air exchange to get the water out faster. But after a while as the filament dries, there is less water coming off and water escape from the dryer slows. That’s when things like a dry air purge or desiccant in the chamber become more effective and even necessary to get humidity even lower. But desiccant in the chamber is heated so has reduced effectiveness.
Using a small dry air purge (~2% RH) and no initial venting by propping the door open, I tend to be at 20% RH with a full spool of filament in 10-12 hours. I’ve found that to be good enough for PETG HF and PLA though I’ve been experimenting with stopping PLA a little earlier (~22-24% RH) but not much experience with those numbers yet. May just keep it simple and take everyone to 20% though there is no need I’m aware of to dry more than what is needed to get good prints.
Anyway, that’s at temperature. When I put spools dried to 20-24% RH into a poly box with a hygrometer, it pegs the hygrometers at 10% RH in short order as the spool cools. (More evidence of hot desiccant not holding onto water - or conversely, cool desiccant holding water more strongly - the filament is desiccant too.) Prints don’t have moisture effects then.
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Yes, oops that was a typo, I’ve fixed it. Since the beginning, I have treated my filaments with some care. 
I have been using our kitchen oven. Which can use force air, convection etc and accurately hold whatever temp I set it from 35degs upwards within 2 degrees. It can take 6 reels. So quite a nice unit, except the wife objects to me “cooking” plastics. Hence, the SUNLU. I have been storing the reels using a cooking vacuum sous vide sealer thing.
I take your point about the desiccant, I have now removed it so I am now testing the Sunlu on drying just plain air. It seems to stabilize at about 18%, cracking open the lid a bit, and it’s dropped to 16%. So I am guessing that maybe 15% is rock bottom.
Interesting about your statement that the RH drops from 20% to 10% when the filament is boxed and cooling. I really don’t have the space to use boxes, so utilize sous vide bags instead. I do insert a 50mg desiccant bag.
I am shocked to see some filament dryer photos with water drops inside, that’s really wet
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Yeah, I tend to think that photo is staged. As the chamber heats up water will be less likely to condense. While the chamber is cool, there won’t be enough energy to get the water to want to leave the filament wholesale to cause that kind of moisture release to condense on walls like that. Plus, the most water I’ve had leave a spool was still less than 3g IIRC. If not it was certainly less than 4g. That water shown in the photo looks like significantly more than that. But if the room it was in had windows open in winter or similar, maybe?
You can actually calculate what the RH will be in heated air if you know the starting humidity and temperature. If you take air at 40% RH and 25C and heat it to 55C, the humidity should go to around 6% according one online humidity calculator where I just ran the numbers. That’s the principle these things work on. Where they fall flat is real world limitations on air exchange and air mixing in the dryer and having a water source (the filament) constantly adding water to the air. That’s where filament in the dryer seems like a good idea and it can be with other types of desiccant than silica gel. Drierite can absorb lots of water at relatively high temperatures - higher than silica gel.
About desiccant bags, they are great to use like that to scavenge water as long as people keep them fresh/dry. Let them sit out to absorb water from the air, or if they just get old from sitting in filament bags/boxes, and they can absorb enough water that they can become a water source. If you do a search on silica gel, a lot of articles are about using silica gel to humidify display cases in museums to keep contents at some optimum humidity level. You just put the beads into a chamber of the right target humidity and let them equilibrate. Then when they go into display cases or whatever, they give up or take water depending on conditions but their water content and capacity kind of makes them a water buffer.
Thanks, I’m learning from you Ok just to clarify something. I have just run the Sunlu empty, door closed for 10hrs @ 70C the display settled at 15 RH%. Now let’s say I reduce the heater temperature to 50C then the RH% will increase, is that right?. According to our central heating thermostat, the room is 50 RH%
That is correct - Cool the air and RH increases. 50% RH is pretty significant for ambient humidity.
Thanks for the detail, I somehow assumed that once you heated the air and the moisture was cooked out/evaporated, let’s say it’s now at 15 RH%. That was it, this percentage is fixed independent of temperature. It’s kind of hard to get my head around as to what’s happening. We just seem to be moving the moisture from one object/place to another. So in the case of filament, we heat it to expel the moisture. Then we have to put it in a hermetically sealed container to limit or slow the filament re-absorbing the surrounding moisture. As you said, it’s acting like a desiccant. I did try changing the Sunlu temperature. At 70C it was stable at 15 RH%, I then reduced the temperature to 50C, the RH increased to 36 RH% Anyway, At least now have an idea of what the endpoint RH% should be after X hours of drying vs temperature.
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I realize this is an old post but I got here looking to dry 10yo Hatchbox PLA. my old printer died long ago and I couldn’t afford to replace it. I just bought the A1 and I love it! I also ordered 4 spools from Bambu, not realizing they would come without spools. I have 3 almost full spools of 10yo PLA and was concerned about them having sat in Ziplock freezer bags for that long. Last night in an effort tor get up and running I pulled out one of roles and set the A1 to generic PLA and set up to print a reusable spool. It printed flawlessly no stringing or bubbles. So I am not sure about the whole needing a dryer. I do have a roll I am going to try tonight that has been unprotected for the same 10 years, I will update this post after trying it I will also add pics.
Maybe you live in a low humidity climate? I have read that some folks don’t ever bother to dry PLA. I think that your bigger problem is how to utilize the 4x Bambu refills. Perhaps you can return them, and buy the filament with spools? The cost is perhaps $4 per reel more. Or just keep the refills and buy more Bambu filament on reusable spools. A bit of a bummer.
Yep - the water we’re talking about as humidity is already evaporated. The mass/volume of water in air won’t change until you start condensing water out.
You can take air at one humidity, heat or cool it to another temperature and the relative humidity will change (its ability to hold moisture). But take it back to original temperature and the humidity should return to the original value as well.
Some relative humidity calculators will tell you the mass of water vapor in a volume of air at a specific temperature and relative humidity. You can then do calculations the other way and see what the relative humidity will be for that mass of water at different temperatures.
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That was surprising to me at first because ziplock bags aren’t that great for keeping moisture out. I need to try a freezer bag but the regular smaller (and thinner) Ziplocks let water through. I filled one with dry air and sealed it with a hygrometer inside and over days the humidity increased to near ambient.
But ice in freezers gradually sublimates away because of the very low humidity in the air in a freezer. I think that 10 years in a freezer was maybe similar to 10 years in a dryer?
Really curious how the spool not in the freezer makes out!
No need to send back the spools, just print some re-useable bambu spools from either Makerworld or the file included on the SD card that came with the printer.
Good info. I presume that is preferable to use a higher temperature tolerant filament for the spool
Yes thats the standard practice I believe. But I found just printing them in PLA is also fine as long as you don’t use them for drying purposes.
Ok, got it. When you use the Sunlu S2. Do you pay much attention to it’s RH indication?
Here is the recommended temperature chart for the Sunlu. Isn’t the ABS temperature on the low side?
PLA/ DIA+ WOOD PETG 45-50°C
ABS PVB ARS PVA ASA TPU PMMA 50-55°C
PA/PC 60-70°C
All 3-6h baking Time
It wasn’t in the freezer, it was just in a Ziplock freezer bag with a small pack of desiccant like the ones that come in the spools.
I’m impressed! The freezer bags are thicker. Maybe they have a water block layer?
I do but my method/setup isn’t stock. I know the onboard hygrometer may not be very accurate but it seems repeatable. I started drying until it hits 19 or 20% and pull the spool to go either in the AMS or a poly cereal box for storage. That seems to get me past all the water issues.