I have just taken delivery of a H2D Combo and HT dryer.
The printer is working fine and both AMS behaving OK with filament loading and retrieval but not performing as expected in reducing humidity.
Observations:
I get lower humidity overnight with drying function switched OFF at around 17% - both units indicate a similar reading. (!)
I have tried multiple cycles to reduce humidity level with just a single filament rolll loaded in each unit. But could not get below 18%. even after a 10 hour cycle
Dessicannt supplied by BL loaded in both units with packaging removed
Latest firmware applied to printer and AMS units
I am currently running both AMS units with reels EMPTY to see if humidity drops using the filament drying cycle but after 2 hours no drop in humidity
Something is not working properly!
Constructive sdvice welcome!
Support ticket lodged after noting the humidity stayed at around 19 % for both AMS Pro 2 and the AMS HT even with no filaments loaded after over 3 hours. Definitely may doing the job!
If the temperature in your house was 20C at 20%RH and you raised that to 55C, I’d expect that to be very dry air, like under 5% RH. Sorry I don’t have one to try.
Humidity sensors that provide precise values below 20 %rH or above 85 %rH are getting quite expensive and I heavily doubt that Bambu puts an expensive sensor in the AMS units.
I wouldn’t worry too much about the displayed value (unless it’s 25 %rH or more). If the set temperature for drying is reached and the color indicator of the dessicant has the “dry” color (which is orange with most modern indicators added to silica gel) I would ignore it.
I keep my filaments in dry boxes with a lot silica gel usually around 15 %rH (measured with a precise device) and before it even reaches 20 %rH, the silica gel has already absorbed so much water that the color indicators clearly show it.
Silly question, but do they actually get hot? Even at 100% RH 20C you shouldn’t have any problem getting to 15% RH at 55C.
Unless, of course, they simply forgot to load the sensor temperature compensation table and you are reading the raw partial pressure. That’s just too crazy.
On my way out the door, plugged the power cord into a HT and set it for PET 80C. Starting rh was 27, temp 24. Desiccant removed.
First time using the dryer mode, but it behaves very strangely, the rh didn’t drop as it heated but only when I opened the top. Seemed reproducible and it just doesn’t go down unless the lid is open. This was only over 5 minutes so the plastics were probably de-gassing themselves.
It’s been running now for about 12 minutes at 81C and is down to 7%. Guessing this is too high?
Sorry can’t play with it more now, I’ll leave it running and see if it drops more.
It took me a while to figure out how to turn mine on, don’t take offence, are you sure you are triggering the AMS dryer and not the bed drying mode? Does the temperature on the AMS display change? The rh seems too high on mine but even so it got down to 7 pretty quick empty (after I opened the lid a few times).
As mentioned several times, RH is a misleading metric because it doesn’t tell you how much moisture is actually present in the system—only how saturated the air is at the current temperature. I posted a photo earlier showing my AMS HT with different filaments, and two of them hadn’t been dried or had the lid open for quite a while.
If you dry ASA for eight hours you might see the RH drop to around 10%, but the spool still isn’t dry at that point. Once the heat is turned off and it’s left to sit, the RH will climb again within a few hours.
One effective method—if you have the time—is to load your AMS HT and AMS2 Pro with desiccants and run them at the highest setting for at least 24 hours before drying your first spool.
If you actually want to know whether a spool is dry, you need to weigh it or calculate AH instead of relying on RH.
Thanks to all who have responded - some good tips there.
here’s some results:
The comments I made were in relation to PLA with both AMS dryers indicating around 45degC for the drying process which appears correct for PLA. Both AMS’s are displaying active drying mode.
With filament reels removed I could not get the indicated RH below 18% after 3 hours. Again internal temps were 45deg C with fans audible.
I could not however identify any exhaust from either AMS vent.
I note after printing last night, the indicated RH gets up to about 30% with the same PLA loaded back as previous tests. Despite this high RH printing is OK
I gave both units another drying cycle overnight and this time the AMS Pro 2 pulled the RH down to an indicated 14% which is the best result so far!
However, the AMS HT did not perform as well with an indicated RH of 18% after the same overnight drying cycle. This reading is after about 11 hours drying eSun PLA @ 46 degrees C.
The RH after printing last night in the AMS HT rose to about 30% so it appears the AMS HT dryer is at least partially performing - reducing RH rom 30% to 18%. but not great
I purchased the AMS HT after reading your encouraging response to my thread on purchasing a dryer for the H2D. Thanks for your further clarification above. There was a range of views on AMS HT performance to that thread with Hotel Lonely reporting similar disappointing results. it appears these AMS HT dryers do vary a lot!
Photo 2 Overall Status of both AMS units 20/11/25 after full drying cycle with both PLA filaments installed. Both units had temps of around 45 deg C fans running with newBL dessicant installed.
Awaiting a response from BL Support. There is no apparent reason why the two dryers have underwhelming performance. I suspect an issue with the vents not releasing moisture or RH sensors well out of spec.
That’s an odd one. Guessing there may be a difference in sensors? As a data point, my AMS 2 Pro at work goes down to 0% when I dry filament. Stays there for a while before slowing rising over a few weeks.
Which ambient temperature and humidity do you have in the room?
This plays a big role on how deep air humidity can drop when you heat the air in a dryer.
Please also note, that the measured humidity does not directly indicate the filament moisture. I think, 45°C and round about 15% RH could be sufficient for PLA. When you place an actual roll in the dryer, it first has to heat up the role throughout. Then, moisture has to slowly make its way out of the roll. I think after initial drop, the air humidity will stay almost constant for a very long time in your environment. During that time, humidity will escape from the roll and flushed out through the vents.
If you want to see lower humidity readings, set temperature to 80° and observe the measured air humidity.
I think a much better test would be drying an actual roll that caused problems like stringing, so it is presumably wet.
You can see if the drying was successful if the roll lost the expected amount of weight. For 1kg of PLA i would expect 2-3g at most, which would be perfectly plausible.
Interesting observation and you may be correct the displayed RH is not accurate.
I may purchase a professional RH device and do a check - but feel the AMS units should be more accurate given the level of the H2D printer and cost.
Thanks for the advice and I think your comments are pretty spot on.
I don’t have any “wet” filament to try but I will leave a roll out and do the weight checks as suggested. I don’t have a RH measurement device but ambient temp is around 20 degrees C. I will purchase an accurate RH device shortly.
The bottom line is my prints are fine with filaments mentioned in this thread.
However, I would like the AMS units to display accurately.
