Automotive Electronics Practice Test

Series-wound electric motors are known to produce maximum power at what condition?

1. At low RPM

2. At high RPM

3. At a constant speed

4. At 0 RPM

The correct answer is: At 0 RPM

Series-wound electric motors, also known as series motors, are designed such that the field winding is connected in series with the armature winding. This configuration allows the motor to develop maximum torque at low speeds, which is particularly useful in applications requiring high starting torque, such as in electric vehicles or cranes. At 0 RPM, the motor has the ability to develop maximum torque because the current flowing through the series field winding is at its highest. Since the torque produced by a series-wound motor is directly proportional to the armature current and the strength of the magnetic field produced by the field winding, maximum torque aligns with low-speed conditions where the motor starts accelerating from a standstill. As the speed increases, the back electromotive force (back EMF) rises, which reduces the armature current, and thus the torque diminishes along with the motor’s ability to produce power at high speeds. This behavior is particularly important in applications where rapid acceleration is necessary from a stop. Overall, the characteristic of series-wound motors to produce maximum power at 0 RPM is due to the high current and associated magnetic field strength, which supports powerful start-up performance, differentiating them from other motor types that might excel in higher RPM conditions.