Rosahl M-1J1R Dehumidifier Mounting Cover Drybox

This is a mounting cover/frame for a Rosahl M-1J1R electric dehumidifer membrane which can be used for a filament drybox of around 20-30l for multiple spools. Along with a USB-C power supply module it's a convenient and low power consumption dry storage solution.

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-1J1R membrane is suitable for storing multiple filament spools in a storage box of around 20-30l. 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.

Printing

The cover is just a single part and can be printed without any supports. I printed with Overture PLA Professional on a Prusa Mini+. A .3mf file and pre-sliced .bgcode file is available along with the STL model.

Assembly/Mounting

The cover can be held upside-down to desired mounting position for marking the mounting holes. I found it works best to drill a first hole and then insert a screw into that hole to fix the position and then use the cover to drill the subsequent holes. I used a 3.5mm drill to compensate a bit of tolerance while drilling the holes.

Next the hole for the cables needs to be drilled. Its position is the center of the four surounding mounting holes, see picture, hence it's easy to mark. Do not drill larger than 5mm to allow for proper sealing with the rubber sealing ring.

Finally the larger hole for the membrane has to be marked and cut out with e.g., a Dremel with a cutting disk. Alternatively a round hole could be drilled to the center of the membrane area with e.g., a step drill down to 20mm. The M-1J1R gasket is large enough.

The cover has a compartment for the USB-C power supply module. Solder two cables to the back side of the power supply module and feed them through the hole and sealing ring. Alternatively you can solder a pin header.

The contact terminals of the M-1J1R membrane are quite large and soldering directly to them is challenging. It's more convenient to use 90° flat connectors (see below list of parts). Those are original made for crimping a cable but small wires cannot be crimped well and cables which cna be crimped well are too big to go through the cable hole and sealing ring. Best is to solder the cables to the flat connectors which works way better than soldering directly to the membrane contact terminals.

Parts Needed

The Rosahl M-1J1R dehumidifier membrane is available here, same for the USB-C power supply module here.

• Sealing ring for cable feedthrough (10/6mm outer/inner diameter, 2mm width): https://www.amazon.de/gp/product/B07JGCGQGT/
• 20l storage box: https://www.amazon.de/gp/product/B07P4SC8TQ/ (I prefer those over the often used Ikea Samla boxes because they come with a decent sealing/gasket.)
• 4.8mm flat connector: https://www.amazon.de/gp/product/B07GRH2Y71/
• 6.3mm flat connector: https://www.amazon.de/gp/product/B07BDNR5CQ/
• M3x20 screws plus nuts/washer (length would depend on the box wall thickness used)
• optional hygrometer: https://www.amazon.de/gp/product/B0BXRDWYG2/ (I prefer these over the commonly used cheaper black ones since they measure down to 10%RH and use an easier to source CR2032 battery instead of those LR-something silver oxide cells)

A kit with the M-1J1R membrane, USB-C module and above parts (except the storage box) are available here.

Comments

Yeah, the Rosahl membranes are not cheap but they are crazy efficient when it comes to power consumption with less than 1W 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.