The AMS 2 Pro is designed to dry filament, but there is nothing in the specs to suggest it could dry silica gel desiccant inside the AMS. The best way to find its effectiveness at drying desiccant is to run an experiment.
Normally, silica gel is dried in an oven set to 120C for an hour. This removes almost all the moisture stored in the silica gel. The effectiveness of the drying is measured by placing the desiccant in a sealed glass jar with an accurate hydrometer. Typical readings show a room temperature relative humidity of 7.5% and a dew point of -15C (dew point measures the weight of the water vapor contained in a cubic meter of air and does not vary with temperature).
The following experimental protocol was followed.
1. Leave a 50g packet of silica gel exposed to the air in the house for a week. This will become saturated with water vapor. When placed inside the sealed jar for several hours, the hydrometer stabilized at 47% RH and dew point of 11C, the same conditions in the house.
2. Remove all filament and desiccant from the AMS 2 Pro. Place the desiccant in the center of the AMS.
3. Set the AMS Dry Cycle to 65C and duration of 12 hours.
4. When the Dry Cycle completes, let the AMS cool off to room temperature for several hours.
5. Remove the desiccant from AMS and place in the sealed glass jar with the same hydrometer. Wait at least an hour before reading the hydrometer.
For this test, the hydrometer RH was 7.6% and dew point -14.9C. Within the measurement error, these are the same readings as the oven dried desiccant. The AMS 2 Pro may be less effective at drying desiccant when fully loaded with filament and the 40g of desiccant supplied by Bambu in the slots. I also use 300g of desiccant fitted between the filament feeds. Regular manual use of the AMS Dry Cycle should keep the RH low without the frequent oven drying required with the original AMS.
Now all we need from Bambu is an automatic drying function firmware update that triggers whenever the humidity exceeds a user specified threshold and may run automatically from the external power input with the printer turned off. The AMS 2 Pro could then automatically keep the filament dry even if the printer is not used for several months.
I think, the test in the jar does not really indicate if the dessicant is fully dried. Instead, I propose to weigh it before and after drying. Eg, dry it inthe oven at 120°C, then weigh it. Let it soak until weight has increased by at least 15%.
Then dry it in the AMS and weigh it again.
Where is that information from? All datasheets I found specify between 120 and 150°C for drying. None contains a minimum drying temperature. I think, I read somewhere, that 65°C is a temperature where silica gel stops taking up humidity.
Ran the experiment today. Place the Bambu AMS desiccant with colored balls in a damp bathroom last night. By morning, the balls had turned a dark purple. Placed the desiccant back in the AMS and set it to dry for 4 hours at 65C. The balls had all turned back to orange at the completion of the cycle.
How much would you expect the weight to increase in the silica gel is left out at 50% humidity for several days?
When the desiccant and hygrometer were placed in the glass jar, the air in the jar was at 50% humidity. A few hours later the desiccant had absorbed the excess moisture in the air reducing it to 7.6% humidity. The same result is achieved by using the oven dried silica gel. Both examples are equally effective at removing moisture from the air.
I think that can vary hugely depending on ambient humidity and temperature and the brand of silica gel. For some brands you can find specifications how much water they can take up in different environments.
But to see if the dryer has dried it completely, just compare the weight after drying in the AMS to the weight after drying in an oven. If you achieve the same weight, the AMS probably removed all water.
