"CDU" in the context of model railways typically refers to a "Capacitor Discharge Unit." A CDU is an electronic device used to provide a burst of power to the turnout (switch) motors, particularly those with solenoid-based mechanisms. Here's why a CDU is commonly used:
Reliability: Turnout motors, especially older solenoid-based ones, often require a sudden burst of power to operate reliably. Without this burst, they might fail to throw the turnout, resulting in derailments or other operational issues. A CDU ensures that there's always enough power for the turnout motor to operate effectively.
Prevention of Electrical Interference: When you throw a turnout, it requires a significant amount of current. This sudden demand can cause electrical interference on your layout, affecting other trains and accessories. A CDU helps to mitigate this by providing the extra current locally rather than drawing it from the main power bus.
Reduced Wear and Tear: Using a CDU can reduce wear and tear on your turnout motors. By providing a quick burst of power, the motor doesn't have to strain for an extended period, potentially extending its lifespan.
Smooth Operation: Capacitor discharge units can provide a smoother, more consistent operation of turnouts compared to direct power from the main bus, particularly on layouts with complex track configurations or where multiple turnouts are thrown simultaneously.
In summary, a CDU is a useful accessory on a model railway because it enhances the reliability and smooth operation of turnout motors while reducing potential electrical interference and wear on the equipment.