The main material of the ring varistor is ZnO or SrTiO3, and the electrode is made of silver electrode or copper electrode.
The volt ampere characteristic of ordinary resistor obeys ohm's law, and the volt ampere characteristic of ring varistor is nonlinear. When the ring varistor voltage is lower than the rated voltage, the resistance of ring varistor is very large, equivalent to ordinary resistance, and when the ring varistor voltage to reach or exceed the rating, ring varistor will instantly from the high impedance state into a state of low resistance, working current increases sharply, when the voltage is lower than the rated voltage,ring varistor will restore to a high impedance state.
The ring varistor is used to eliminate the electromagnetic noise and spark generated by the micro motor in the commutating moment.
One of the important note it, when the working voltage of the ring varistor exceeds its limit voltage, the ring varistor will not be able to repair itself, which can easily cause damage. The ring varistor is intermittently working and cannot be in the working state for a long time, otherwise it can be easily damaged. Therefore, it is necessary to consider the matching problem between ring varistor and motor working voltage.