The problem with most filament dryers is they don’t actively exchange air to get rid of filament moisture the heat drives off. On humid days, if they do exchange air, they can even add humidity/water to filament. I started out trying to get a Sunlu S2 to dry better and had some success, but the underlying issue seems to be they need dry air pushed through them to let the heat do its work. Commercial dryers seem to do ok on low humidity days with doors propped open to get air exchange.
I’m working on a cheap air dryer and pump using various ideas some of us have bounced around. I’m waiting on a couple more parts to do a full test but am hopeful this can help a number of dryers. It’s just an air source and is pretty much guaranteed to work. The only questions are if the output air is dry enough and if it can run long enough to dry filament rolls. It uses hygrometers to monitor performance of each stage.
If it works like I hope, it will be a small source of dry air to plumb into existing commercial filament dryers. I’ll know in a few days how it does. Last bits arrive tomorrow and Wednesday.