I'm using DB-036 which is also catergorise under the AD series... from wat i know it take time to stable at the %RH u wan... and take freaking long... and it too so long... by the time it stable, i took out my camera for photoshoot and put it back, its unstable again... quite irritating one... have to keep looking out at the %RH value...
anyway, i think ur question abit strange... u set at 30%-40%... and ur RH is dropping below 50%, isn't it good?,,, coz its moving toward ur desired 30%-40%
Your RH setting is too low, might result in some damages (rubber, lube). 45-50% is recommended (see manual of your dry cabinet).
Have you checked that the door is properly closing? If RH doesn't reach outside levels (70-80%) then the dehumidifier still works outside humidity somehow sneaks in. Alternatively you can get a second RH meter to verify the readings.
Don't worry too much about the times that it needs to reach target humidity. It will always need a few hours, depending on volume of the dry cabinet and amount of humidity brought in with the equipment. A neck strap can carry a lot and many people recommend to remove it anyway before putting the cam into the cabinet.
Camera equipment is meant for usage outside and can stand much more than what we think
Like Octarine mentioned, that figure is too low and you risk damage to rubber and drying lubricant.
For Nikon, I iirc the recommended period for storing is below 60 will do. And storing means if you are not going to use it for a few months.
Fungus don't grow overnight :bsmilie:
Anyway, the control knob is sort of a rheostat only and is not a climate control. So it will fluctuate relatively to ambience changes. So it will fluctuate. I've got both the 30 liter and the 70 liter one and the 30 liter both also fluctuate between 50~60.