Inductive and capacitive couplings in DC motors with built-in damping chokes

A quantitative analysis of parasitic coupling between elements of a 12 V DC motor and its damping chokes is presented. This analysis deals both with inductive couplings between several chokes as well as armature windings, and with capacitive couplings between chokes and the motor casing. It produces a motor model to take these effects into account. It is shown that while both types of coupling depend on the orientation of the chokes within the motor, inductive couplings do not have much effect on its high frequency impedance. The capacitance between choke and casing, however, can significantly influence the impedance of the motor in critical frequency ranges, such as the FM radio band