Motion-Based Energy Harvesting Devices for Railroad Applications

As the story goes, a wise railroad man once declared: Power is the king! Although he was referring to the motive power that we need to move freight, the same could be said about the availability of electrical power on railcars. This is mainly due to the fact that the onboard applications of many smart devices that can add to the efficiency of rail operation are hindered by the lack of availability of electrical power. In this paper, innovative solutions to provide a distributed source of electrical power for railroad onboard applications are presented. In a suspension of a railcar, mechanical energy is dissipated in dampers or wedges and, therefore, wasted in heat. Meant to be placed inside the coil springs of the suspension, the proposed vibration-based electromechanical systems are designed to harvest part of that wasted energy and turn it into useful electrical power. The energy produced is then conditioned and stored in commonly available batteries. The possibility of realizing the mechanical-to-electrical power conversion without any prior transformation of the mechanical input is first investigated. This aims to avoid inherent losses induced in such processes. The prototypes use an arrangement of magnets that moves linearly with the suspension inside one or several coils. The variable magnetic field thus created generates a voltage. The prototypes prove that it is possible to use a translational generator to provide enough power for recharging batteries under conditions commonly experienced in railcar operation. The second generation of prototypes investigates the idea of transforming the input translation from the suspension into rotation and then using a rotary generator. The advantage of developing such a concept is the possibility of including a gearbox to increase the generator speed of rotation. Maintaining high shaft speed is the key to harvest more power and reach higher efficiencies. The output power is improved even more by adding a mechanism that rotates the generator shaft in the same direction independently of how the suspension is moving (jounce or rebound). Both designs prove they can recharge batteries under commonly experienced conditions. But although the linear generator shows some limitations in terms of power (up to a few watts RMS), the rotary generator design demonstrates significantly higher efficiency and greater output power (40Watts RMS with a sine wave input of ±0.75in at 1Hz). The amount of generated power can be augmented by increasing the amplitude and/or the frequency of the input, customizing the generator, and bringing new improvements to the mechanical part of the system.