Thread-Mount Cover for Rosahl M-3M1R Dehumidifier Membrane

This is an new/alternative mounting cover for the Rosahl M-3M1R membrane and USB-C power supply onto a filament dry storagebox, BambuLab AMS or Creality CFS or other multi-material-system or generic storage boxes for various applications. The threaded mounting simplifies preparing the enclosure/box with just one large round hole being required.

There still exist the older non-threaded M-3M1R mounting cover.

Operation Principle

Rosahl dehumidifiers are based on a solid-state polymer membrane. When supplied with a 3V DC voltage, moisture on one side is being decomposed into Hydrogen ions and Oxygen, the Hydrogen ions pass the membrane and recombine with air Oxygen to moisture again on the other side and get discharged. The Rosahl dehumidifiers are compact, work fully mainenance-free and the power consumption is very low.

The Rosahl M-3M1R membrane is suitable for storing multiple filament spools in a storage box of around 50-80l or Bambu Lab AMS or other multi material systems. With pre-dried filament spools (especially spools made of cardboard contain quite high moisture) a continous storage at approx. 15% rH and less is achievable. See pictures of the humidity measured in a BambuLab AMS 2 Pro.

Multi-Material-Systems

A Rosahl membrane is a great addition to any (properly sealed) multi-material-system like e.g., the BambuLab AMS or Creality CFS. The threaded mount cover only requires 7mm of clearance inside hence usually does not conflict with any spools inside.

The membrane is very low-power (2W continuously) and can hence be operated 24/7 without issues ensuring always dry filament in a multi-material-system. After around 24h the humidity usually drops below 20%RH and decreases further over another 24h. See pictures of the humidity measured in a BambuLab AMS 2 Pro with a hygrometer at 16%RH and the AMS integrated humidity sensor reporting 13%RH.

The Bambu Lab AMS sitting on top of the P1P/P1S/X1C printer gets passively heated a bit during print operation and hence further reduces relative humidity inside the AMS and makes the M-3M1R even more efficient!

Printing

The mounting cover is made of four parts, see pictures. All can be printed without any supports needed. The inner fixture requires a bit of bridging, so please check in the slicer if it did chose the proper bridging direction. The large threads in the inner part and the nut are M42 x 1.5 and usually print without issues.

I added three parts with different thread length (10mm, 15mm and 20mm), choose the one best suited for your specific wall thickness. For a multi-material-system with around 3mm walls or a standard storage box with thin walls, the 10mm variant is usually fine.

I also added three nuts with different tolerance clearance (0.0mm, 0.1mm and 0.2mm) which you can select depending on your print quality. 0.0mm does not mean there is no clearance between thread and nut because a regular M42 thread already has little clearance by definition. The 0.1mm and 0.2mm just add additionaly clearance to satisfy printing tolerance.

I printed with PETG on a Bambu Lab P1S. A .3mf file is available along with the STL models.

Assembly

The picture should make the mounting sequence clear.

• The membrane goes flat into the outer cover part plus the VREG-2 USB-C power supply module sliding into its compartment. Which one goes first doesn't really matter.

• Connect the membrane with the VREG-2 (most simple is getting one with pre-assembled cables and flat-connectors).

• Insert the smaller rubber o-ring into the recess of the inner part (the one with the larger thread). It usually stays in place when then sliding the inner part on top of the membrane. Make sure the o-ring stays in its recess to ensure proper sealing. You can flip the outer part with the membrane up-side-down and keep the membrane with a finger on the connectors in place and slice it over the inner plastic part.

• Add the four M3x20 screws from the front and the M3 square nuts from the back and tighten the screws. Make sure to not tighten the screws too much. The back of both inner and outer plastic parts should be flush without any step.

• Add the small VREG lock part. This ensures that the VREG module stays in place when inserting a USB-C connector later.

Mounting

I added a printable drill-guide as STL which you can print on your printer and use it to find a good place and mark either the center of the hole when using e.g., a step-drill (recommended) or round hole-saw (can be risky with thin walls or brittle material) or mark the outline of the hole when e.g., drilling a sequence of small holes around the diameter and finishing with a file.

If going for an MMS setup it might be best to unmount the cover before driling. However, kept it mounted and just added a foil over the bottom part and closed the cover and all shavings were kept by the foil. Up to you.

When the hole is done properly you can slide through the previously mounted set. One of the larger o-ring goes into a recess around the outer thread and another larger o-ring goes into a recess of the nut. Add the nut and screw together until the o-rings have a tight fit.

Finally add a USB-C cable and connect to a USB power supply/charger. In case you would prefer the USB-C connector on the opposite side, you can simply mirror the outer part before printing.

Parts Needed

The Rosahl M-3M1R dehumidifier membrane is available here, same for the USB-C power supply module here, which is now available fully assembled with cables and crimped flat connectors.

• 50l storage box: https://www.amazon.de/gp/product/B0CLDT4815/ (I prefer those over the often used Ikea Samla boxes because they come with a decent sealing/gasket.) or a Bambu Lab AMS or a Creality CFS or other MMS!

• 1x 4.8mm flat connector: https://www.amazon.de/gp/product/B07GRH2Y71/

• 1x 6.3mm flat connector: https://www.amazon.de/gp/product/B07BDNR5CQ/

• Rubber sealing rings (1x 45mm inner diameter, 2mm cross-section, https://www.amazon.de/gp/product/B07FY9ZYYD, 2x 50mm inner diameter, 2mm cross-section, https://www.amazon.de/dp/B07FY8HH1V)

• 4x M3x20 screws plus M3 square nuts

• Step-drill covering 42mm hole diameter e.g., https://www.amazon.de/dp/B0CND5TL1M

A kit with the M-3M1R membrane, USB-C power supply module and required parts for mounting is available here.

Oxygen Increase Inside and Fire Hazard…?

Air density at sea level and 20°C is 1.204kg/m^3. Percentage of Oxygen is 20.94% so we have 252.1g Oxygen in 1m^3 of air. A relative humidity of 60%RH at 20°C corresponds to an absolute humidity of 10.37g/m^3. When we reduced this down to 10%RH, which corresponds to 1.73g/m^3, we have split 8.64g of H2O into Hydrogen and Oxygen and transported the Hydrogen to the outside. H2O is composed of 2x Hydrogen with a molecular mass of 1g/mol and 1x Oxygen with 16g/mol, so the Oxygen share of the above 8.64g H2O is 7.68g. So, we have increased the overall Oxygen in 1m^3 from 252.1g to 259.8g and hence increased the percentage from 20.94% to 21.6%.

Given this minimal increase, there is no need to worry about any negative impact of Oxygen concentration inside a Rosahl membrane based storage box.

Comments

Yeah, the Rosahl membranes are not cheap but they are crazy efficient when it comes to power consumption with less than 2W continously. I leave them running 24/7 without the need for ever re-drying a spool in a conventional filament drying or oven which would require significantly more power.