In this paper, a self-excited induction generator that can act as an electric retarder is presented, and an effective control method and circuit for enacting it are proposed. To control braking torque, the equivalent circuit parameters of the retarder are changed by switching the proposed circuit. Even though the retarder is a high-voltage high-current ac machine, it uses readily available and inexpensive components including a low-voltage high current-ratingMOSFET, diodes, and a polarity capacitor. Dynamo test results show that the proposed circuit and method is effective.