Electric generators are described herein. The electric generators include an interior machine formed of an interior rotor and an interior portion of a stator, and an exterior machine substantially concentric to the interior machine. The exterior machine includes: an exterior rotor substantially concentric to the interior rotor, and an exterior portion of the stator. Each of the interior machine and the external machine are driven by an engine to produce a respective current. The described electric generators can be used in diesel electric locomotives.