The typical spectrum of the electrical noise of the dc motor is a very wide and chaotic pulse, and in many cases, the electrical interference level will exceed the limit (EMC) if necessary suppression measures are not taken.
The electrical noise of the dc motor is the peak voltage, which is mainly generated by the motor brush. It is caused by the disconnect between the brush and the commutator. The capacitor is used to bypass the voltage spike by providing a low impedance channel to the public end of the noise source.
The capacitance can be connected to the ground between each lead of the motor, or between two leads. Access capacitance between the brush and the ground will be very effective. Another way to reduce noise is to place an inductance device directly on the brush. The effect of inductance is to prevent the sudden change of the current of the brush when the brush passes through the gap.
The inductance of the inductance is about 10 ~ 25 mu H. The choke coil in series can be combined with the by-pass capacitance of the ground to form a low pass filter, which can enhance the filtering effect of a single inductance or capacitor. The conventional method is to add ring varistor directly to the motor process.