The Sanpla Dry Keeper Automatic Desiccator uses a granular desiccant to dehumidify the inside of the cabinet to about 30-40 % RH. The desiccant is held in a basket equipped with a heater for regeneration when saturation is reached.
The instrument goes through a 30 min regeneration phase followed by about 4-5 hours of moisture removal. This cycle is controlled by a mechanical switch driven by an AC synchronous motor.
The instrument in our lab didn’t work any more, meaning the %RH was constantly about 60. I began to take the device apart to do some troubleshooting. After removing the lower front cover, a door was visible. This door is opened during the regeneration cycle to get rid of the trapped moisture in the desiccant. During normal operation (moisture removal) this door is closed and another similar door on the inside is opened to expose the desiccant to the inside air. A fan circulates the air to enhance effectiveness.
It turned out the AC synchronous motor driving the mechanical switch was faulty. It didn’t deliver enough torque and frequently stopped moving. The dehumidifiying/desiccant-drying timer cycle (5 hrs/30 min) resembles that of an defroster timer cycle used in freezers. I therefore wanted to give it a try and see if I can modify the equipment to use a defrost timer. This is the model I chose: Paragon Defrost Timer, Model# A1400-00. it has a 6 hours cycle with 21 min “defrosting”.
As anticipated the new timer was too big to fit to the inside of the desiccator module. A new place had to be found. After disconnecting the wires from the old timer (right side of picture) I drilled a hole into the plastic enclosure and fed 3 wires to the outside, two to power the AC synchronous motor, one to be switched by the timer. On the inside I connected the 3 wires to the appropriate counterparts that were once soldered to the defective timer terminals.
The new timer was then mounted on the outside of the desiccator module with the 3 wires connected to it. The photo shows the finished work. The module was put back in place inside the desiccator cabinet and powered up for a test run. So far the modified desiccator module works fine, the humidity inside the cabinet is about 25% RH.