At what speed in MPH do dynamic brakes start to function?

Dynamic brakes typically begin to function at speeds around 15 MPH. At this speed, the train can utilize the dynamic braking system effectively, which relies on the traction motors to act as generators when the train needs to slow down. This process involves converting the momentum of the train into electrical energy, which is then dissipated as heat through resistors.

The operational efficiency of dynamic braking is dependent on a balance between the speed of the train and the ability of the braking system to generate sufficient resistance. If the train speed is too low, the dynamic braking may not be able to produce enough braking force to be effective. Thus, 15 MPH is the threshold where the system is designed to engage optimally, providing a significant aid in slowing down the train without relying solely on traditional friction brakes.