Non-contact recharging system watches

Watches recharged by using a charger are called rechargeable watches.

For wrist watches, the ordinary contact recharging method is not practical as it could lead to deterioration on a watch's quality characteristics such as water resistance. In this regard, however, a non-contact recharging system can be employed, so that the watch can be recharged without opening the case back when it is simply placed on a charger. 
When a watch is placed on a charger, an alternating magnetic field is created, which induces an alternating voltage in the internal coil of the watch. This induced voltage is rectified and stored in the energy storage unit to power the quartz watch.

The mechanism of non-contact recharging system watches is explained below.

1. Place the watch on the charger.
   
2. An alternating current of approximately 20 Hz is applied to the primary coil inside the charger to produce an alternating magnetic field.
   
3. Across the secondary coil inside the watch, the induced voltage is generated based on Faraday's law of electromagnetic induction.
   
4. The alternating voltage induced across the secondary coil is rectified and stored in the secondary battery.
   
5. The secondary battery transmits the electrical energy to the driving circuit to run the quartz watch.

Refer to the illustration below.