I still do like my filament dry...but a little bit different this time

What the hell is going on? Why something new?

Not long ago I wrote about my filament dry storage solution which worked for a long time.

Yeah, there are several reasons

  • As one can see from this image, the bottles don't really hold a big volume of liquids. Gaswaschflaschen
  • The liquid is a solution of lithium chloride. The "recycle" that relatively expensive and towards metals not very friendly salt, I had to boil it down in a glass beaker. Not really funny. I only did that twice during the years of usage but I recently updated my setup to a 4 spool roller with balance and more system which has not one but for passthrough for filament from the drying/storage box into the printer chamber, so I expect the amount of water to be absorbed increases. A bigger gas wash bottle system inside the chamber isn't my favorite solution either.
  • With TPU it's rather easy to make airtight connections for my acrylic plate chamber. 



New technical implementation of an old solution by a mad scientist

As I mentioned above, LiCl2 isn't really cheap and therefore I looked out for another salt well known to be hygroscopic: Calcium chloride

I can get 5kg CaCl2 for the price of 100g LiCl2.

Many people use it packed in small bags which are placed in a plastic chamber on top of a sieve. It absorbs the water from the air and the dissolved salt drops into the lower side of the plastic chamber. 

Using such a off the shelf thing would work, but then again it can be done way cheaper (not calculating my time....) 


So, here's the plan:

  • GPIO47 of my Spool Holder provides a PWM signal driving a small laptop fan
  • The fan pushed air from the storage chamber through hoses into an air drying box, containing CaCl
  • The rising pressure pushes the now dry air back into the storage chamber

Control cycle:

  • Humidity is measure every few seconds.
  • Once the value stays above the specified max level for longer than 60 seconds, the fan is switched on
  • The inflow of dry air decreases the value measures and as soon as it remains below the min level for more than 30 seconds the fan is switched off
  • Data is published to my mqtt broker

That finally leads to the following control chart


The blue jigsaw line is the measured humidity, the blue "areas" between 0 and 10% shows when the fan was actually turned on. The reddish area/topline is the temperature.The thin vertical lines are my min an max level

So far I'm good with that. However, there's room for improvement

  • I use the fan in a purely binary mode. Either it's on (90%) or off (0%). Maybe I'll implement a PID one time in the future.

Hardware wise I have printed most parts beside the main air drying chamber on my Ender. The main chamber needs to be really air tight, so I have chosen one with 8l volume which has a tight lid closure.

A first step, drybox filled with desiccant bags:


The next step, 2 ice cream containers with calcium chloride



And the final step. A 3D printed box,which is placed inside the bought box. The air flows along a 60cm stretch of distance along the CaCl2.

DehumidifierDehumidifier with airflow

Where the air flows in an our


Remarks and conclusion:

Again a completely over engineered design. But hey, YOLO