DCC Basics


On this page of the DCC Hobby Supply Website we'll be presenting a series of articles over the next few months concerning the basics of Digital Command Control or "DCC" as it commonly called today. It will be my goal in the next few months to (hopefully) present information of value for those of you who are new to DCC. Whether you're planning to invest in and install a DCC system or not, it is undoubtedly near the top of the list of most significant developments available to model railroaders today. So let's take a brief look at what DCC is and what makes it different from the traditional DC control systems of past (and present) years. First of all, when model trains are powered in a traditional DC system, 120 volts AC house current is first changed to approximately 12 volts DC by your power pack. Then that DC current is sent out through the track to your locomotives in any quantity from 0-12 volts or so, making it possible to vary the speed and direction of your trains. This is the first really big difference between the two types of control systems. In DCC a step-down transformer must still be used, however the 120 volts AC from your house service is reduced to around 16 volts but remains AC current. This AC current is present in your layout's track at all times, whether trains are in motion or not! The power in the rails is always on: around 12 volts or so for N scale and 14 volts for HO, a little more in the larger scales. So what is it that allows the locos to vary their speed and direction? The simple answer is, "the decoder", which every DCC controlled model train must have. It is the decoder that receives or "decodes" the DCC information (called "packets") that is sent through the track by the command center of your DCC system. All the functions of a particular locomotive, whether it's the lights, the speed, the direction, or even sounds, are controlled by the engine's decoder. One bit of information concerning train speed that I find fascinating is that in traditional DC operation if we want our train to reach say 35% of its top speed we turn a rheostat or potentiometer so that 35% of the 12 volts available is reaching the loco's motor. In DCC if we want the same 35% of top speed we turn our digital encoder up to 35% but we still have full power coursing through the rails. The difference is the power is only being sent out for 35% of the time! That's but one small reason why train control is normally more precise on DCC layouts. Next time we'll review the major components of a DCC system. In the meantime, if you have questions or comments, I would welcome your emails or phone calls.

Happy Railroading!

John Thut