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.
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 CaCl₂
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

ControlchartSML

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:

Drybox_Step