With the humidity inside the PolyDryer boxes being roughly proportional to the amount of filament on the spool, I printed a slightly modified airlock plate and a TPU seal ring, then stuck a tiny fan on it:
It just barely clears the curved air guide inside:
The tea bags full of desiccant allow some wind between them and the filament in the spool, but I obviously must re-think that setup. There’s enough clearance for what should be reasonable circulation, so i defined it to be good enough for now.
The box of TPU started at 25 %RH, dropped to 22 %RH overnight, then returned to 25 %RH the next day:
Now that I’m watching more often, I’ve seen the meter glitch to 10% for a few seconds:
A humidity indicator card suggests the air is under 20 %RH:
It may be the filament can outgas water vapor as rapidly as the desiccant can remove it, but I expected the fan to make at least a little difference.
I have no idea what’s going on in those boxes.
The Smell of Molten Projects in the Morning 
Comments
4 responses to “PolyDryer Internal Fan Puzzle”
is there any particular reason to think the digital hygrometer actually works? Whatever happened to your hobo loggers?
The meters started out close to the basement’s 50 %RH and decreased inside the boxes, so they’re behaving plausibly, and the indicator card shows the meter’s value is at least in the right time zone.
The glitches to 10 %RH are worrisome.
The Hobo loggers keep busy logging things around the house and I’m just now getting to the point where I often/em> remember to dump them once a month; it’s better if I don’t disturb that habit. :grin:
perhaps the photo’s color balance is misleading but the card certainly looks like well below 10%, and even at that a 150% error seems … problematic:). What does it say when the dryer box is empty, I wonder?
I’ve never been good at judging those colors, but the 10% card seems closer to being “Lavender”. The accuracy of each spot might be ±5%, as it’s chemistry at work, so the meter is likely pessimistic.
Unless all the meters are kaflooie in the same direction, which is certainly possible. I have another hygrometer that won’t quite let the spool turn, but … for science.