A portable power source (10) includes a housing (12), a stator component (20), a rotor component (18), a crank assembly (14), and a control system (24). The stator component (20) is secured to the housing (12), the rotor component (18) rotates relative to the stator component (20) and the crank assembly (14) is coupled to the rotor component (18). The crank assembly (14) is rotated by the user relative to the housing (12). As provided herein, rotation of the crank assembly (14) by the user results in rotation of the rotor component (18) relative to the stator component (20). In one embodiment, the control system (24) controls the amount of torque required to rotate the crank assembly (14). For example, the amount of torque required to rotate the crank assembly (14) is varied according to the rotational position of the crank assembly (14).