What is DCC?

What is DCC and why should I choose DCC? What are the advantages of DCC over traditional DC control of locomotives and layouts?

Digital Command Control (DCC) as defined by the National Model Railroad Association in the US, is a universal standard for controlling model railways. Locomotives and components of a layout such as points and signals can be controlled by DCC systems.

Put simply, DCC allows multiple locomotives to be controlled independently from one power source supplied to the track. N scale DCC systems typically output approx. 13.8V AC, that use slight modification of the frequency within the current itself to transmit digital signal (e.g. 0’s and 1’s). These digital signals are read by every locomotive on the layout, but are only relevant to one particular locomotive or consist*. These signals can control a locomotive’s motor, lights and sound functions (if equipped with these features).

Each locomotive on a DCC layout must have a decoder fitted. A decoder is connected directly to the track through the wiring of a locomotive, and acts as a mediator between the track power, and the motor, lights, speaker etc. (if fitted) to a locomotive. The decoder is able to turn on/off and deliver variable current to each of these various features. Each decoder has a particular number address programmed┬║ on it, typically ranging from 1-9999. This gives the decoder and locomotive an identifying ‘address’ that allow digital signals from the command station to be addressed to one particular locomotive (or consist*).

For example, a NSW 44 class diesel locomotive numbered 4490 operating on a DCC layout could have a decoder installed inside programmed to the 4 digit address ‘4490’. All locomotives on this DCC layout will receive digital signals addressed to ‘4490’, such as drive forwards, turn the forward light on, but only the decoder in 4490 addressed ‘4490’ will carry out the actions of these signals.

Breaking up a layout into lots of switchable power isolation blocks is no longer needed, and locomotives can be run much more prototypically with controllable functions such as lights. Large DCC layouts are separated into power districts as the command station has a limited output of current, requiring the need for boosters powering further districts. The command station can be maxed out by a large number of operating and stationary locomotives, particularly when operating a significant number of sound locomotives. Stationary locomotives are always drawing a very low current, which depending on how many locomotives are on the layout can add a noticeable overall current draw. It is best to always over-compensate for how much load could be drawn in any given power district, and to prevent the impact of short circuits. When a locomotive or metal wheel set create a short circuit on a DCC layout, the system will shut off track power until the short circuit is cleared, which is very disruptive and noticeable for locomotives in operation, particularly those that are fitted with sound. The advantage of having more districts is that the impact of a short circuit is limited to the specific district that it occurs in.

*Consists

A consist is a group of DCC equipped locomotives that can be controlled in unison, double/triple/quadruple heading or a lash up.

┬║Programming and Configuration Variables (CV’s)

Programming refers to the ability to change various features/settings that a decoder has. These features are identified as ‘configuration variables’ (CV’s). Each CV has a number e.g. CV29, and using a digital number based system, values of 0-255 can be stored for a particular CV. Within a CV, particular numbers between 0-255 denote different qualities of a feature or setting, and/or may turn on or off a particular feature or setting.

What components do I need to run a DCC layout?

All that is needed to run a DCC layout is a command station, and an appropriate throttle or controller (usually of the same brand as the command station). A command station is similar to the power supply for a DC layout, as it uses mains power and typically requires a separate controller. However it also contains computer processing to create the digital signals that are sent through the track to locomotives, as well as capability to manage controllers/throttles, points and signals, and communicate with desktop computers.

Some command stations are presented in the form of a controller themselves, while others will require you to use a throttle that is connected to the command station via a RJ12 connector (as used in the Digitrax LocoNet system, a 6 pin phone cable). Some command stations will allow you to directly connect to them via in-built WiFi or via a separate WiFi module, allowing the use of smart phones and tablets. The majority of command stations will allow connection to a computer via USB to use various software programs, typically JMRI. I highly recommend JMRI, you can read more about it here: http://jmri.org

Common DCC systems available in Australia include:

  • Digikeijs – DR5000 3A command station
  • NCE – PowerPro, PowerCab
  • Digitrax – Zephyr Express, Evolution Duplex
  • ESU – ECoS
  • Roco – Z21
  • Lenz
  • MRC
  • EasyDCC
  • Third party WiFi throttles (not systems)
    • WiThrottle iPhone/iPad WiFi throttle
    • TCS UWT-100 WiFi throttle