What is the ideal range of humidity for drying, how high is to high?
I haven't measured it. I hang in a closet for 3-4 days, opening the door a few times to exchange moist with dry air. I go by how it feels, then cut them down to fit into a Sterlite plastic container. I manage the drying using a Caliber 4 hygrometer inside the plastic container. Seems like they're about 80-88% when they first get into the container. Another 4-5 days opening, fanning, etc, the plastic container.
I haven't used the $25 humidity controller yet. I think that will be *much* easier. Step 1) Turn the fan on when it's over 85% in order to dry it to that level quickly (couple days?). Step 2) Simply push the down-arrow on the controller's face to lower the setting 2% every day. Let it do all the work monitoring humidity, turning on the fan. In 10 days, 65%.
I think how long it would take (how aggressively anyone would lower the setting) would depend on their climate's humidity. I'm in a dry area, so what I described above should work well. If I were in Florida, I might make step 1 = 70%. (I.e., it may not need 2-degree steps every day like I do.).
The controller has a "differential" feature which lets you specify the humidity difference between on/off. How far below "on" conditions the humidity must drop before going off. That would give some control over how fast it goes down. (In my dry climate I think I need only 1% differential so the fan will run more frequently, less often. More like a constant trickling operation. The controller also has a feature to specify how much time must elapse between on/off cycles so it isn't too twitchy. I might need to use that feature so it's not turning on/off too rapidly.).
This seems like a great way to do it. No guesswork about whether 40 volts is enough. Let the controller do the work. You just adjust the variac so the fan produces a calm flow. You don't have to care if it's enough. The controller does that job. If it never turns off, then you know it's not enough.