What occurs if the load is removed from an operating series DC motor?

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Multiple Choice

What occurs if the load is removed from an operating series DC motor?

In a series DC motor, the field winding is in series with the armature, so the magnetic field strength depends on the armature current. When the load is removed, there’s almost no opposing torque, so the motor speeds up. As speed increases, the back-EMF grows, which reduces the armature current and thus weakens the magnetic field even more. That weaker field means the motor loses the ability to generate torque to oppose further acceleration, so the speed climbs until some limit stops it—usually a mechanical or electrical limit like bearings, insulation, or supply constraints. In practice, this can lead to a dangerous runaway condition, which is why the motor may continue accelerating until it fails.

In a series DC motor, the field winding is in series with the armature, so the magnetic field strength depends on the armature current. When the load is removed, there’s almost no opposing torque, so the motor speeds up. As speed increases, the back-EMF grows, which reduces the armature current and thus weakens the magnetic field even more. That weaker field means the motor loses the ability to generate torque to oppose further acceleration, so the speed climbs until some limit stops it—usually a mechanical or electrical limit like bearings, insulation, or supply constraints. In practice, this can lead to a dangerous runaway condition, which is why the motor may continue accelerating until it fails.

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