Digital Command Control makes reliable, realistic train operation and simplified layout wiring a reality. With DCC you control multiple trains independently on the same section of track without
blocking. In the real world, engineers control the speed and direction of real trains. Engines operate under their own power independent of the track. Each engine has its own motion characteristics
such as how fast it speeds up (acceleration) and how long it takes to slow down (momentum). A locomotive's performance is influenced by whether it is operating alone or as part of a multiple unit
lash-up. The weight of the train also affects its performance. DCC gives you reliable control over all these variables.
With DCC, train operation depends on the decoder installed in the locomotive. The track is powered by a command station and/or booster connected to a transformer. Each locomotive operates
independently over the track. Several locomotives can be moving at different speeds and in either direction at any time on the same electrical section of track. Blocking is not required for train
control. It's easy to move engines around in the yards and park them close to one another without worrying about where the insulated sections are. It's easier to operate trains in the wide open
spaces, too! DCC lets you run your trains instead of running your track.
The NMRA Digital Command Control Standard defines the basic communications structure at the track level for digital control signals via the rails. The standards specify a communication protocol
between transmitter and decoder without specifying transmitter and decoder hardware. The data needed to operate each decoder is transmitted in packet format on the rails in the form of a balanced
square wave. This baseline packet format allows for interoperability among equipment made by different companies that support the standard.
Interoperability is the most important advantage of the standard. Interoperability means that if you have a DCC compatible decoder, you can run it with any DCC compatible command station. This is
very important since the major part of your investment in any DCC system is in the decoders. We have all heard the horror stories: "I have a fortune invested in this equipment and now I can't even
get spare parts any more much less expand my system!!!" Any system that is available from more than one source is not as likely to disappear and leave its users stranded. Also, having equipment
available from multiple suppliers creates competition in price and features to the benefit of the end user.
The standard does not cover the actual command stations or control equipment used to operate the decoders or the features they offer. You can buy a full-featured DCC command station or a basic DCC
command station. You can spend more money or less money. There is a place in the market for both low end and high-end equipment. You decide what makes sense for you and your railroad.
What can DCC Do For Me?
DCC has advantages for everyone from the beginner to the advanced modeler and for every layout from the smallest to the largest. For beginning and intermediate modelers (most modelers classify
themselves at this skill level) the advantages of reasonably priced simple command stations and simple layout wiring are very important. Start with a relatively low cost command station and add
components as your interest grows. If you decide you want more advanced features and functions from your command station or if you want to add a computer, it's an easy transition from basic to
full-featured command stations. The equipment you already own moves on with you as you add more features to your system. Your largest investment in time and money is in the decoders you install in
the locos. These are upwardly compatible as you expand and add to your system. By simply adding components you can grow into a more advanced system at your own pace and as your budget allows.
Most home layouts are small or medium sized. They typically have a limited amount track available for block control. DCC has a real advantage in these situations. Since blocking is not required you
can operate more locos in a smaller area.
For the large home or club layout DCC offers truly prototypical operation and minimum wiring hassle.
Modular layouts running with DCC can operate more than 2 or 3 trains at a time. Let's face it, the outside loop running clockwise and the inside loop running counterclockwise all day isn't very
exciting. The ease of wiring makes modular hook up simple and lets you get operating sessions up and running more quickly.
What Are The Components of a DCC System?
All DCC systems are made up of various components that are connected by a command bus. Generally, DCC decoders and boosters are interoperable and DCC command stations are not interoperable. This is
because each DCC manufacturer uses its own command bus structure. The way communications are handled by any given system are very important to overall system performance and to system expandability.
When you are making your decision about which system to choose we recommend that you look carefully at what each manufacturer's of bus structure has to offer. Some factors to consider are ease of
hook-up, ability to run multiple devices without slower response times, future expansion capabilities and overall system architecture.
Digitrax's LocoNet is a collision sense multiple access bus with carrier detect. Lenz's X-bus is a "polled" bus. Wangrow/NorthCoast bus is similar to X-bus. As other manufacturers enter the market
they are adopting their own communications structures.
Components of DCC systems
To create a DCC system you will need each of the following:
One Command Station (to generate the command signal)
One or more Power Supplies (for power to run the locomotives)
One or more Boosters (to combine the signal with the power and put them on the track)
One or more Throttles (to send your commands to the system)
One or more Mobile Decoders (to decode the signal and control the locomotives)
Most DCC Manufacturers provide everything you need (except for the transformer) in starter sets.
Optional equipment:
Automatic Reversing Devices
Accessory Decoders for turnout and other accessory control
Programming Devices
Signaling and Detection Devices
What if I want to run a regular analog engine?
With most DCC systems you can run one analog locomotive (without a decoder) along with the digital ones. This lets you convert your fleet gradually. You may also have some locomotives are too small
or too valuable as collector's items to be converted but you still want to run them on your DCC layout. If one of your friends brings his unconverted locomotives over to run on your layout, your DCC
system can probably handle it. And it goes the other way too, if you want to run your DCC equipped locomotive on a regular DC layout, many DCC decoders automatically convert to DC operation if there
is no DCC signal present. Check with your manufacturer about the availability of this feature. Analog locomotives tend to "sing" when sitting still on DCC layouts. This noise decreases as the analog
locomotive accelerates and runs. The noise is caused by the DCC track signal. This noise can be significantly reduced by using conductive brush lubricants such as Aero-Car Technology's "Conducta" and
by assuring that there is no vibration inside the locomotive that will add to the noise generated. It is best to park your analog locomotive on an un-powered section of track when it is not running
to cut down on heat build up inside the engine.
Track Wiring Considerations
Now let's turn our attention to track wiring. You will need to consider your layout power bus wiring, your command bus or network wiring and in some cases separate feedback bus wiring. With DCC the
signal and the power go hand in hand so your locomotive must have good conductivity to insure reliable train control. DCC is more tolerant of dirty track than some other command control systems
because of the fact that DCC commands are sent over and over to the decoders. Periodic track cleaning will still be needed.
Track Wiring
Early proponents of DCC touted the fact that you can hook up your railroad with just two wires. While this is technically correct, there are some issues that need clarification here. If you are
wiring a new HO layout it is a good idea to use at least 12 gauge wire with feeders to each rail every 10 feet or so as a power bus. If you have an existing layout, the general rule is that if you
can run regular DC engine around the layout, the wiring should be able to run DCC without problems.
Unless you need to section your layout for added power, the only gaps you need are for hard shorts such as reverse loops and un-insulated frogs. If you are already wired for block control, you
probably don't need to rewire to use DCC. Just open all your blocks so that the entire track has power and you are ready to go. If you are using common rail wiring and you wish to section your
layout, you will need double gaps to separate the sections.
Reasons To Section Your DCC Layout.
Even though blocking is not required for train operation with DCC, sectioning the layout has two advantages:
1. To provide additional power to operate more locomotives than one power supply can handle. For example a 4 amp booster and power supply will operate between 6 and 10 average N-scale locomotives,
between 4 and 6 HO locomotives and 2 to 4 G scale locomotives. You can run more equipment by sectioning the layout and adding additional boosters and power supplies. For large-scale operations you
can use higher current boosters to deliver more power to individual sections if needed to run more trains. Just a note about boosters and current ratings: most DCC boosters will require an external
fan in order to output the stated maximum current for extended periods of time. This is not an issue for most modelers but if you experience booster shutdown, you should consider adding fans to
increase heat-sinking capability.
2. To prevent total layout shutdown when shorts occur in any given section. If a short occurs in one section, only that section shuts down, the rest of the layout keeps operating. The reason for this
is that all of the boosters are linked to the command station and will continue to receive the DCC signal and output it to their own section of track.
The Dreaded Reverse Loop
You can operate reverse loops manually or automatically using DCC. You must double gap (completely isolate) both ends of the reversing section. If you choose manual operation you will power the
reverse section separately and use a switch or relay to handle the polarity change as the locomotive enters and leaves the reversing section. If you use an auto reversing strategy you will power the
reverse section separately and use an auto reversing booster or other auto reversing device to handle the polarity change. Note that when the polarity change occurs DCC equipped locomotives will
continue at the speed and in the direction commanded but any analog engines running will reverse direction because they "see" the polarity change and respond to it. If you choose the auto reversing
booster strategy, you will need at least two boosters. One will be the system reference booster and the second will be the auto reverser. The good news is that you can run more than one reversing
section on a single auto-reversing booster. Also, note that some auto reversing devices require that you make changes to locomotive wiring where the pickups are not "side by side" on the locomotive.
This is an issue in many steam locomotives where one power pickup is on the locomotive and the other is on the tender.
How Many Trains Can I Run?
The actual number of trains you can run is determined by several factors. Seriously, how much room do you really have to run trains? For most people the answer is "Not Enough!" To figure out how many
trains you can run with DCC you'll need to know the address range supported by your system and your decoders, how much power you will need to run a given number of locomotives and how many throttles
your system will support.
Address Range: DCC systems can access anywhere from 6 to over 9,000 addresses. This is the number of addresses you can assign to your decoders, not necessarily the number of locomotives you can run
at a time. Some decoders can only use "2-digit addressing" others can use both "2 digit" and "4 digit addressing". The advantage to 2 digit addressing is that it is much simpler to use. The advantage
of 4 digit addressing is that you can assign the number painted on the side of the locomotive as its address. Most DCC systems can run both types of decoders on the same layout.
Power Requirements: The number of trains you can actually run will ultimately be determined by the amount of power you supply to your layout. Each DCC booster is rated for between 3 and 8 amps. This
means that you can run as many locomotives as your booster can power. To run more locomotives, you'll need to add more boosters.
How Many Throttles Can Your System Support?: Another factor that determines how many trains you can run is the number of throttles your system will support. DCC systems support from 4 to over 200
throttles. Check with your manufacturer if you are planning to have a lot of operators.
How Can I Customize Each Locomotive's Performance?
Each decoder installed in your locomotives can be programmed to have its own unique personality. When you program DCC decoders, the command station sends programming information to decoders and the
decoders store that information for future use. You do not have to open up the locomotive to program decoders. Just press a few keys and you are ready to go. Each decoder can have a different
personality and it "remembers" its programming until you change it. We use configuration variables or "CV's" to set up various operating characteristics in our decoders.
DCC decoders have a wide variety of features. Not all features are important to everyone so, you will find decoders available in a wide variety of feature combinations and price ranges. The following
is an outline of most of the features available in today's decoders. Check with your manufacturer to be sure whether the decoder you are buying has the features that are important to you. Remember
that DCC decoders are interoperable and you don't have to put the same decoder in every locomotive.
Locomotive Address
The locomotive address is a two digit (CV01) or four digit number (CV17 and 18) assigned to a certain decoder. This is the number you will use to access the locomotive in your system. Some systems
use color designations instead of numbers but in reality, these colors correspond to numbers.
Locomotive Speed Controls
Because DCC is a digital system, discrete speed steps define locomotive speeds. The DCC standard calls for 14 forward and reverse steps for speed control. Some decoders offer advanced 28-step
operation to give you even more speed control. And if that's not enough, how about 128 step operation. With 128 step operation you have extremely fine speed control. You can really make those
locomotives crawl! The ability to take advantage of more speed steps depends on the throttle you are using. The number of speed steps a particular decoder can use is determined by the manufacturer,
some systems use CV29 to set up which mode the decoder will operate in.
Back EMF Speed Control
This is cruise control for your locomotives. Some decoders have this feature that lets you set a speed for your locomotive and have it run at that speed "up hill and down dale." It is also called
load compensation. This is particularly useful for low speed operation when 128-speed step control is not available.
Acceleration and Deceleration Rates
Acceleration is the rate at which the decoder increases speed from one speed step to the next in response to a new increase speed command. The acceleration rate (CV03) can be set to simulate train
weight. Deceleration is the rate at which the decoder decreases speed from one speed step to the next in response to a new decrease speed command. The deceleration rate (CV04) can be used to simulate
inertia. Just like the prototype, you can set your locomotives to get off to a slow start because of a heavy load and to take a long time to come to a stop because of the inertia of the train once it
is moving.
The Throttle Response Curve
It's easy to confuse the throttle response curve with acceleration and deceleration. The throttle response curve is the relationship of the motor voltage (throttle setting) to the speed step command
sent by the command station. Acceleration and deceleration are the rate of change from one speed step to the next up or down.
The Graph below shows the various curves that can be created using V-start and V-Mid adjustments or by programming the user loadable speed table for each discrete speed step.
Adjusting the Loco's Throttle Response Curve.
The default motor voltage/speed curve is a straight line from stop to maximum speed. However, since locomotives don't really accelerate this way, DCC decoders let you alter this speed curve to
simulate prototypical train motion. Let's look at the different ways to control locomotive speed and motion that are available with DCC.
Discrete Speed Steps
Because the signal is digital, the throttle response curve has 14, 28 or 128 discrete speed steps
Start Voltage
You can set the start voltage by using CV02. The higher the start voltage, the higher the locomotive's initial speed when started. This adjustment is used to trim the locomotive to compensate for its
motor efficiency. If you have a locomotive that takes a lot of voltage to get started, this adjustment can be helpful.
Mid Point Voltage
The mid-point voltage adjustment allows the motor speed curve to be altered at step 15, the midpoint of the motor voltage curve by using CV06.
Max Voltage
The maximum voltage adjustment lets you set the maximum voltage to be applied at the top speed step. Use the maximum voltage CV05 to limit the top speed of your locomotives.
Start voltage, mid point voltage and maximum voltage can be used to quickly and effectively set your locomotive's throttle response curve to simulate the prototype.
Loadable Speed Tables
If you wish to be more precise in setting your throttle response curve, loadable speed tables let you define each individual speed step for a locomotive. Once you have defined the speed curve you
like, you can use the forward and reverse multiplier to move the curve up or down in speed.
Setting up a loadable speed table involves setting many CV's since you will set a value for each of 28 speed steps. Many DCC users find that using a computer based programmer makes this process much
easier. When you use a computer, you can even save the speed tables you like and load them into other decoders quickly and easily via the computer.
Can I MU Locomotives?
DCC systems offer three choices for consist control:
The Basic Consisting method is to reprogram all the locomotives in a consist to the same address and run them on one throttle. In this case all the locomotives must be headed in the same direction,
head to tail, head to tail, head to tail.
Advanced Consisting stores the consist information in each decoder. The locomotives can be added to and deleted from the consist in any orientation head to head or tail to tail. This method requires
that all locomotives in the consist be equipped with decoders that support this feature. This method allows you to set up a consist that will be "transportable" from one DCC layout to another but you
must be sure to always put the locomotives back on the track in the same order and orientation you programmed them for or you can get some unexpected results.
"Universal" Consisting stores the consist information in the command station and allows you to consist locomotives with any DCC decoder as well as an analog locomotive. The locomotives can be added
to and deleted from the consist in any orientation head to head or tail to tail.
The number of locomotives you can consist varies widely from system to system.
Loco Lighting and Other Features of DCC Mobile Decoders
In addition to address and motion characteristics, most DCC decoders control constant directional lighting and in some cases offer additional function outputs. DCC decoders usually have at least 2
functions available (sometimes these are set up as directional lights so that your headlights go on and off automatically when you reverse the engine). Large-scale decoders have as many as 8
functions available. Some decoders have special effects lighting built in so that you can activate additional locomotive lighting like Mars lights, ditch lights, cab lights, etc. Additional functions
can be used for smoke units for steam locomotives, sound units, and much more. These extra locomotive functions are accessible from full-featured command stations. Some DCC decoders include a mobile
decoder and sound decoder in one unit.
Programming Decoders and Wiring a Programming Track
There are several ways to program your decoders. Most DCC Command Stations have built in programmers that send programming information as a broadcast message to any decoder that is listening. This
means that you could reprogram all the locomotives on the track with one simple keystroke. To prevent this, it is useful to add an isolated programming track to your layout and program decoders as
follows:
1. Run the decoder-equipped locomotive you want to program onto the programming track.
2. Throw the switch to disable the rest of the layout.
3. Switch your command station to program mode and follow the manufacturer's instructions for programming the decoder.
4. Switch the layout back on and drive away.
Some DCC Command Stations offer a separate programming output so that you can program decoders without shutting down the rest of the layout as described above. Also some systems offer operations mode
programming which allows you to send programming information to a specific decoder on the layout. Another programming option is a stand-alone programmer or a computer based programmer.
Is It Hard To Install The Decoders?
Now that DCC has been around for a few years, locomotive manufacturers are beginning to build locomotives that are more "decoder friendly." This makes installation much simpler than it used to be!
Many new HO locomotives are equipped with the NMRA standard medium plug. DCC manufacturers also build decoders that replace the factory-installed circuit board for many HO locos. If you have one of
those, it's just a matter of plugging in your decoder and programming it. Most other HO locomotives allow relatively easy decoder installation. Do the easy ones like Atlas/Kato Diesels and Athearns
first. Then as your skill increases, tackle the more difficult engines like Rivarossi Steam engines and small yard engines.
N-scale and narrow gauge installations are more difficult because of the limited space available for the decoders. N-scale locomotive manufacturers are working on making their future releases decoder
friendly. Kato's C44W-9 has a light board that can be removed and replaced by a clip in decoder made especially for that locomotive. There are decoders that replace the light boards in the Kato PA's
and E8's. Still another N scale DCC decoder is made for the Atlas GP40-2 and U25B's. If you are using other Atlas or Kato engines in N scale, it's probably a good idea to start with locomotives that
have replacement frames available. These make N-scale installations easy because you don't have to make room for the decoder or the wires, you simply replace the frame and solder in the decoder.
Other N-scale locomotives don't require replacement frames but you will need to modify the weights to fit the decoders inside.
Since almost all narrow gauge installations are in steam locomotives, space is tight! You'll want to consider installing the decoders in your tenders where there is usually more room. Sound is
another issue that many narrow gaugers want to incorporate in their operation and this requires even more room inside the locomotive because of the need to install a speaker, too.
In G-scale locomotives, there is almost always plenty of room inside to install DCC decoders and sound units, too. It is usually easy to see where the wires to and this makes large-scale installation
easy. Beware that large scale locomotive manufacturers don't follow any wire color conventions when they build the locomotives so, it will be important for you to closely examine your locomotive and
determine "which wire does what" before you start your installation. Unfortunately, many large-scale locomotives were not made to be taken apart so, getting the locomotive disassembled is often the
biggest challenge you will face in large-scale installations.
Decoder Installation
Because every engine is different we will cover only the basic concepts involved in decoder installation.
Read the Instructions and Plan the Installation
Each manufacturer provides instructions with decoders. Read them! Take a close look at the operation of the locomotive you want to convert when it is running on regular DC. Installing DCC decoders
will not improve the mechanical operation of your equipment! Prior to installing the decoder is a good time to audit the mechanisms and give them a good tune up (since you already have the shell
off). Be very careful when you take you locomotive apart, don't lose any of the little parts that tend to fly off in every direction. If you decide not to install a decoder in a given engine but plan
to run it on a DCC layout do the tune up anyway. If you are working with Athearn diesels, the November 1993 issue of Model Railroader (Page 106) has an excellent article on tuning up these
engines.
The mechanical placement of the decoder is important and may involve sculpting plastic and or metal parts to allow enough room for installation. Decoders from different manufacturers have different
form factors. You should choose the one that has a current rating appropriate for your locomotive and that fits best in your locomotive. Try to locate the decoder in the coolest part of the body.
Your decoders will provide more power to your motors if they are installed away from heat sources inside the locomotive body like motors and lamps. Try to put them where they can shed as much heat as
possible.
Obviously, the scale you model will have a bearing on the ease or difficulty of decoder installation. In G scale, there is usually lots of room inside for decoder installation, the trick is removing
the shell. Even though decoders are smaller today than ever, it is still a tough job to get them into many N-scale engines. The small size of the HO decoders has made installation possible in most
diesels and steam engines. Some of the smaller switchers still present a challenge and some modelers use the smaller N-scale decoders in these with no problems. For N-scale modelers, Digi-Frames by
Southern Digital (available through hobby dealers or (770) 929-1888 and Aztec Manufacturing (775) 883-3327 2701 Conestoga DR #113 Carson City, NV 89706 produce replacement frames for many popular
Atlas/Kato Diesels. These frames really simplify installation in these locomotives. There is even a frame for the Kato NW-2 in HO.
Determining which Decoder To Use
Measuring Stall Current
The first and perhaps the most important part of decoder installation is being sure you have the right decoder for your locomotive. If the motor's stall current exceeds the decoder's rating you are
sure to have problems down the road so, start by using the following procedure to check the stall current of your motor.
1. Put the locomotive without the shell on a regular DC track.
2. Attach a DC current meter (ammeter) in series with one of the track feeds. Some power packs that have ammeters are really ideal for this test.
3. Apply 12V DC power to the track for N or HO. (16V for G)
4. Hold the flywheel or drive shafts to stop the motor from rotating for a couple of seconds.
5. While the motor is stalled, measure the current that the unit is drawing from the power pack. Be sure that while you are taking the measurement that the power to the track remains at 12V to get an
accurate measurement.
6. Use the manufacturers' recommendations to choose the appropriate decoder for your application.
Generally speaking, N-scale engines with can motors draw about one amp, HO engines with can motors draw about one amp. Older Athearns with open frame motors and Bowers with Pittman motors draw around
1 3/4 amps. Large scale engines (O, S G) vary in current draw and some even have two motors, those with can motors may draw less than 2 amps but each should be tested individually to determine which
decoder to use.
Test the Decoder
Test your DCC decoders before installation by following the manufacturers recommendations. Some manufacturers include basic test kits with starter sets; you can easily build your own decoder tester
or purchase one of the commercially available models. You can save yourself a lot of troubleshooting time if you perform this test first to be sure that the decoder you are installing is working
before you put it in your locomotive. You can do this test for new decoders and for ones that you are moving from one locomotive to another. You will need a test lamp and a protection resistor to
perform the test. Instead of using an actual motor, locomotive lights and functions, use a test lamp to be sure the decoder is functioning properly. Use a protection resistor to avoid any damage to
the decoder caused by wiring errors. If you are a first time installer, this procedure will have the added benefit of familiarizing you with the decoder wiring before you do the installation
Decoder Diagram
Once you have chosen the right decoder and tested it, it's time to check the installation instructions once more. Pay particular attention to the decoder wiring diagram provided. Be sure you know the
purpose of each wire and can identify where it should be soldered to the locomotive. In general decoders follow the NMRA DCC standard recommended wiring colors, but it's always best to check just to
be sure.
Note that several different types of light bulbs are used in locomotives and some lamp installations may require that you use current setting resistors to prevent the bulbs from burning out. Be sure
to follow the manufacturers instructions concerning light installations.
Isolate the Motor
For DC permanent magnet powered locomotives, the decoder must be electrically inserted between the track power pickups and the motor brushes. The most important part of any successful locomotive
conversion is proper electrical isolation of the motor brush connections, so that they are driven exclusively by the decoder circuitry.
Note: Failure to isolate the motor will damage the decoder.
Once the motor is isolated, you can proceed to follow the manufacturer's wiring diagram for installing the decoder.
Test your installation on DC and DCC
Once you have completed the installation, test the locomotive with decoder installed to be sure it runs properly on DC (if available on your system) and DCC. Address the locomotive, run it in both
directions, turn the lights on and off and try out any other functions you installed.
Program your decoder's personality
Refer to your manufacturer's instructions for programming the various CV's to set up your decoder to run the way you want it to. If you are just getting started, it is probably a good idea change the
address right away but to run your locomotive in the default settings for a while. This will allow you to learn how to operate your system and become comfortable with all the new variables you have
control over. Later you can go back and change acceleration, deceleration, speed curves, etc.