Hygrometer for Filament Dryers (Sunlu S1 and eSun eBox)

The Sunlu S1 and eSun eBox unfortunately don't come with a built-in humidity gauge. But there are cheap mini digital hygrometer/thermometers available in many shops  which allows you to easily add one yourself.

My design consists of a base plate mounted into the dryer (no extra screws needed!) and a holder for rectangular or round humidity gouge, which can easily be attached or removed any time, even if filament is already loaded and printing.

The Sunlu mount plate is fixed using the screws of the heating metal (added a strip of Kapton tape for some (minimal) heat isolation (although PET(G) should work well without). The eSun dryer (eBox) doesn't have any such screws, but a thin slit which can be used to insert a "blade".

The gauge holders are tilted some degrees to allow easy opening of the cover. And the arm to stick it on the mount plate as a gap at the bottom which is wide enough for the filament to pass through. This way the humidity gauge can be attached or removed any time, also during a print. This is especially useful for the eBox version, because due to the limited space under the round cover, completely full spools might not allow to attach the gauge immediately.
 

All parts can be printed without support. Except for the Sunlu mount plate just lay the models flat. The Sunlu mount plate I printed standing upright - even without support (although some minor bridging is needed, but that was no problem)

As mentioned above, the hygrometers are available from many sources, if you didn't find one yet, this is an example https://www.amazon.de/Vaikby-raumthermometer-zimmerthermometer-luftfeuchtigkeitsmesser-Gew%C3%A4chshausautos/dp/B09WDVSLZ4/?content-id=amzn1.sym.0bf9ab1e-db90-4058-8c91-2e3e5b4712b7

And this design can also be found on Thingiverse: https://www.thingiverse.com/thing:5502676

Small update (2022-09-16): If the Sunlu S1 is operated on maximum heat for a longer time (I use this setup to also dry my silica bags), even PETG mounted directly to the heating metal gets a bit soft and the front plate might not stand perfectly upright any more - it bent a bit at the bottom. So far the holder is still working fine though, but I didn't like this minor degradation. As a possible solution I added some small stabilizers on the side (v2) to help keeping the plate upright. I'll keep you posted if this works well long-term.

Meanwhile I printed the mount plate for the Sunlu dryer in ASA, which withstands the heat much better than PETG. ABS is probably also fine - didn't try. But I do not recommend PLA (unless you have a special “high temperature” variant) and also not really PETG for the mount plate directly attached to the hot metal sheet. For the holder itself and all parts for the eSun eBox PETG is perfectly fine as there is no connection to hot metal.

 

Yet another minor update (2022-09-28) to the mount plate for the Sunlu S1. I found something much better to shield the plate from the heat of the metal than just thin Kapton tape: silicone. I cut out a small piece of a silicone mat (actually folded it to have two layers) and put it underneath the mount plate. And voila - no more softening of the plastic even on high temperature mode. To compensate for the thickness of the silicone mat, I raised the bottom by 1mm. Don't worry, the screws are still long enough. I used a piece of silicone baking mat, but any heat resistant mat will do, probably also other material with low heat conductive value like cork.

Update 2022-10-07: Added some little plugs (tampions) to close an unused hole (or both if you only dry Silica bags). They should be printed in TPU (or other flex) for perfect fit (although PLA or PETG will probably also work). The cap of the plugs are available in two sizes: 10mm and 12mm. I personally use the 12mm version for the lower (and bigger) hole and the 10mm pin for the upper hole (see picture). The barbel shaped plug for the lower hole need support if printed in one piece - otherwise you can print part1 and part2 separately and glue them together.

Update 2023-01-03: Added an eBox mount plate version with cut-outs at the top bar to allow for slightly larger spools. Not exactly an improvement for stability but will hopefully allow for more filament brands.

Update 2023-02-02: Yet another very minor update for the eBox mount plate as I found even larger spools which almost scratched. I widened the cu-outs a bit (now up to the side wall) and I added a minimal slope to the blade (results in only one extra layer on top half if printed with 0.2mm layers) to slightly improve pressure to the front.

Update 2023-03-04: Added a (rectangular) gauge holder for Sunlu S1 with 10mm longer legs as requested by salut (see comments)

Update 2024-04-19: Added v3 of mount plate for eBox with cut-outs for use with Bowden Adapter (see comments)