DCC control for model railways: all you need to know

23 May 2019
dcclead-02075.jpg DCC controllers for model railways
Dispelling the myths of Digital Command Control – how it works, what it's for, and how you can benefit.

There's a lot of 'buzz words' associated with DCC. Trying to figure out if this method of model railway control is right for you, can be equally confusing.

What is DCC? Why do you need DCC? How difficult is DCC wiring? We'll answer these questions to dispel some of the myths surrounding DCC.  

What does DCC mean?

The conventional method of operating model railways is known as analogue technology using a DC (direct current) transformer/controller. In the simplest of terms, using an analogue system means just one locomotive can be operated by one DC controller (and its transformer) on one section of track at any one time.

If a DC layout has tracks that are electrically isolated from each another it will be possible to move more than one train at the same time on different tracks, but it will be necessary to use one controller to operate one different train on each section of the isolated tracks.

Today, most people entering the hobby opt for Digital Command Control (DCC) because of the control flexibility and opportunities for sounds that it offers. The major advantage of using DCC over DC is that (in theory) you can connect just two wires to your layout, insert a decoder into each locomotive and address them with a unique ID number to control them.

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DCC model railway controllers

With DCC an entire layout is fed with electrical power at the same time. To control the individual locomotives the DCC controller (often known as the cab or throttle) sends instructions to each locomotive via the rails. Each locomotive is fitted with a decoder that receives commands from the controller and converts the signal (or decodes it) into instructions that relate to its movement, the lights (if fitted) and other functions such as sound effects (if fitted). This means that each DCC (decoder fitted) locomotive can be controlled individually without the need for different track sections and many of the wiring complications that might occur if DC control was used.

Each DCC-equipped locomotive is given an identifying address that is a number. So, for example, a Class 31 locomotive might carry the address 031, a Class 150 DMU might be 150 and a Class 57 diesel might be 057. When a locomotive is bought it usually carries the default address 003.

The factory-installed settings in the decoder determine how that decoder controls the locomotive. The purchaser can tailor locomotives on an advanced DCC system to configure the acceleration, braking, lighting and sound effects using CVs (configuration variables).

DCC controllers for model railways

When the person operating the layout wishes to 'control' a locomotive (for example to get the locomotive to move or to turn its lights on or off), the command from the controller must begin with the locomotive’s address (number). When the locomotive picks up the digital signal, the decoder converts the signal received into one or more actions. For example, the signal from the controller might command the locomotive to move faster or slower; to switch its lights on or off, to whistle or to hoot its horn. This takes place as the operator presses buttons or turns a knob on the controller.

The controller might operate other accessories too such as point motors, signals and working cranes.

What are the advantages of DCC?

There are a number of advantages of DCC over DC control. Some of them are down to personal choice, though DCC offers a more varied way to operate model trains.

  • DCC-equipped layouts can operate more than one locomotive at a time using a single DCC controller. They can also operate more than one locomotive on the same track at the same time (this can be quite fun, but you have to keep your wits about you!)
  • Each locomotive that is installed with a DCC decoder has a personal ‘address’. This address is a number. An operator can key in that number on the controller and the locomotive will obey its instructions. Once the instructions have been given to one locomotive the operator may turn his attention to another locomotive. Both trains can be running at the same time using the same controller, until instructions are given to stop the trains.
  • If, for example, a layout has four separate circuits of track the locomotives on all four tracks could be operated by one DCC controller. It would however be necessary to ensure that the output of the DCC system was powerful enough to control four separate locomotives at once.

DCC wiring

The wiring on a DCC layout may be simpler than on a DC layout. On a simple small DCC layout, the power can be supplied to the track through just two wires at one connection without a need to isolate sections of track. Additional wiring may be required for larger layouts to ensure a good flow of current. Some DCC practitioners solder each track connection so that the entire layout will maintain a good flow of electricity through the rails. The double heading of trains and use of banking locomotives is also possible with DCC.

Two trains can run into the same platform separately without the need for complex wiring. With a DC system, such a platform would need to have two separately-wired ‘isolated’ sections. The benefit of this facility is even greater at a locomotive depot – an operator can put as many locomotives on the same siding at a locomotive depot as its length permits. And then he can run them around and out of the depot one by one.

DCC provides control over directional running lights of locomotives and multiple units, interior lighting effects, on board sound effects and smoke generators for steam locomotives. Some of these are possible on DC locomotives but are much more familiar and accessible on DCC locomotives.

DCC locomotive lights can be turned on and off at the operators instructions. With most DC locomotives, the lights gradually get brighter and dimmer as the locomotive builds up speeds and slows down. DCC lights are usually of constant brightness rather than needing to run a train at high speed to see the lights working as often happens with DC locomotives. Even on compact layouts, the lights on a DCC locomotive will be bright. 

Some DCC locomotives additionally feature controllable couplings, opening locomotive doors and pantographs. And if you want to fit (or buy carriages with it fitted) carriage interior lighting, you can use DCC and it’ll stay lit at a constant brightness even when the train is stopped at a platform.

Accessories such as signals, working cranes and point motors can also be operated by DCC - all from the same controller as you run your locomotive. Some modellers do choose to operate these accessories on DC power though. The layout owner has the choice.

For more advice about wiring your layout, watch these basic tips on working with wire in both DC and DCC. 

What are some of the disadvantages to DCC?

  • Some worry that DCC will be all too complicated. Many have operated a DC layout successfully over a period of years and may not want to spend a lot of time looking into DCC. While it is essential to read the manual supplied with any DCC equipment, some modellers may decide that they want a new challenge in the hobby and DCC may represent this.
  • Some feel that there is an elitist air surrounding DCC operation. There are certainly many experts in the field but do not be put off by its apparent complexities. Using DCC can be as simple as you want it to be.
  • DCC locomotives need to be fitted with decoders! Fitting decoders to locomotives has got easier because most models today are sold ‘DCC Ready’ with sockets to take decoders. Others come DCC Fitted with a decoder already installed.  You can either ask the manufacturer if it is possible to retro fit a decoder or look on the web – there are many sites that contain useful information.
  • DCC locomotives are more expensive than DC locomotives. Sound fitted locomotives are dearer still. Whilst decoders are now available from less than £10 each there will be an additional fitting charge if you decide to get someone to install the decoder for you.
  • It is not always possible to fit a DCC decoder into older and smaller locomotives.
  • There are a lot of manufacturers producing DCC equipment. Looking at all those adverts and demonstrations at model railway shows can be confusing. It is always best to see the different systems in action and choose the one that is best for you and your layout.
  • Another drawback is the number of buttons you need to press to control any locomotive, turnout or signal on your layout. With the proliferation of sound locomotives with many functions and modellers wanting motorised points and multi-aspect signals, control of these is becoming more complicated.

Can I operate DC locomotives on a DCC system?

Usually yes. Some DCC controllers permit one DC locomotive to be operated though the layout is wired for DCC. Check the manual to see whether your DCC system permits this. The downsides of this are that the DC locomotive emits a buzzing sound when used with a DCC controller that doesn't occur when the locomotive is driven under DC power.;

DCC controllers for model railways

What does ‘DCC ready’ mean?

You’ll often see new locomotives specified with either ‘DCC ready’ or ‘DCC fitted’. Put simply, ‘DCC ready’ means the locomotive has a socket fitted which is set up ready for a DCC decoder. The locomotive can also still be used on a DC layout.

If the locomotive states it is ‘DCC fitted’, that means the model already has a socket and a decoder already fitted, so will be ready to use on a DCC track immediately. These locomotives usually cannot be used on a DC track.

How to fit DCC sound decoders

DCC sound decoders are available with a range of steam, diesel and electric sound projects pre-loaded. Most are easily installed into DCC-ready models, so long as they fit into the available space. They make updating locomotives simple and are available from a variety of manufacturers with prices to suit all budgets.

Many modellers are put off by the idea of fitting their locomotives with sound because they’re concerned that a great deal of work will be required, however, that doesn’t always have to be the case. There’s also a level of flexibility if you stray from the basic kit.

How easy is it to convert old locomotives to DCC?

A lot of locomotives today come ‘DCC ready’, but if you’ve got an older locomotive that isn’t, there should be plenty of advice and guidance on manufacturers website on how to convert the model.

Read our article on how to convert a J64 to DCC.

More information

If you still have any questions regarding DCC that we’ve not managed to answer here, there are a number of articles available in our dedicated section here

If you’re after more hands-on advice on setting up a DCC decoder properly, view our easy-to-follow tutorial here.