CDUs are a common component on many model railways, but what are they?
In simple terms, a CDU – short for Capacitor Discharge Unit – is an electronic device that makes the operation of certain types of motorized points on your model railway more reliable and less likely to cause derailments. It can also help protect the motor driving points.
The longer answer is that some point motors need a lot of power to operate, and it may be that you don’t have enough power on the layout to operate them. When this happens, either the points don’t change reliably, or your trains slow down when they do. CDUs work by storing up an electrical charge and, when you need it (to change the points), release it in a powerful, short burst.
There are various types of point motors available, but CDUs are for solenoid-type motors such as the Gaugemaster SEEP PM1, Peco PL10, and Hornby R8243 motors. These work by using electromagnets to move the bar which connects to the point to move the rails. However, the amount of current on your model railways may not be enough to create activate the magnets and thus move the points. This is often an issue if you have numerous points or turnouts operating from the same power source or points that are far away from the power source – power is lost over long runs of wire.
This is where a CDU comes in handy. It is connected to a power supply (16V AC) and builds up a reservoir of current ready to be at the flick of a switch. Different capacity CDUs are available to cater for operating different numbers of points. This Gaugemaster CDU for example can power up to 6 points simultaneously.
In conclusion, CDUs can improve the reliable operation of your model railway. They’re relatively low-cost and worth trying if you are having problems with solenoid point motors. If you found this article helpful and want to know more about model railway electronics and track work, subscribe to my free email newsletter.
Andy is a lifelong modeler, writer, and founder of modelrailwayengineer.com. He has been building model railways, dioramas, and miniatures for over 20 years. His passion for model making and railways began when he was a child, building his first layout at the age of seven.
Andy’s particular passion is making scenery and structures in 4mm scale, which he sells commercially. He is particularly interested in modelling the railways of South West England during the late Victorian/early Edwardian era, although he also enjoys making sci-fi and fantasy figures and dioramas. His website has won several awards, and he is a member of MERG (Model Railway Electronics Group) and the 009 Society.
When not making models, Andy lives in Surrey with his wife and teenage son. Other interests include history, science fiction, photography, and programming. Read more about Andy.