DCC for Railway Modellers E-Book

Fiona Forty

• Herausgeber: The Crowood Press
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 241

Veröffentlichungsjahr: 2024

Beschreibung

Written in layman's terms, DCC for Railway Modellers gives an in-depth overview of Digital Command and Control. Informed by the author's extensive knowledge of DCC and model layouts, this book will give both the novice and experienced modeller a comprehensive breakdown of DCC and model railway standards. covering topics such as: The history of DCC, Components of DCC, Decoders – DCC, Sound and Function, Fitting decoders, Layout design considerations and wiring and Troubleshooting

Leseprobe

An area of Peter Annison’s layout Martin's Creek, a logging railway.

Hornby Tender Drive decoder installation.

CONTENTS

1History of Digital Command Control and the NMRA

2Digital Command Control

3Common Misconceptions and Myths

4Wiring the Layout

5Track Design

6The Basics of Wiring and Soldering

7Locomotive Maintenance

8The Basics of DCC Systems

9Locomotive Decoders – DCC and DCC Sound

10Fitting Decoders

11Accessory Decoders

12General Troubleshooting

Appendix

Glossary

Index

1

HISTORY OF DIGITAL COMMAND CONTROL AND THE NMRA

Digital Command Control (DCC) is a system for the digital operation of model railways. When equipped with Digital Command Control, locomotives on the same electrical section of track can be independently controlled. The DCC protocol is defined by the National Model Railroad Association (NMRA) and overseen by its Digital Command Control Working Group.

Lionel Trains electronic control.

Early Systems

It may be surprising to learn that a version of DCC has been around since the 1940s, when Lionel Trains introduced a two-channel system called Magic Electrol. This used frequency control via a device in the locomotive called the E-Unit, and allowed two locomotives to run at the same time in opposite directions on the same track. In the 1960s, GE introduced a five-channel control system known as Automatic Simultaneous Train Controls (ASTRAC for short). This allowed five locomotives to run at the same time on the same track.

Hornby Zero system setup.

Airfix multiple train control system.

In the 1970s and 1980s, several more companies jumped on the control-system bandwagon:

•Dynatrol CTC-16 by Power Systems Inc. was a 16-channel system that appeared in 1979. Based on the Digitrack 1600 system, using integrated circuits, it could be built by following a series of articles published in Model Railroader magazine, beginning in December 1979.

•Hornby Zero-1 was a true digital system, introduced by the UK manufacturer Hornby to the USA in 1980 and Canada in 1981. Based around a Texas Instruments TMS1000, the system incorporated a four-bit microcontroller that was able to address and control up to sixteen locomotives.

•Airfix Multiple Train Control System (MTC) was an analogue-tuned carrier control system, introduced in 1979, which could control up to sixteen locomotives, with a maximum of four at a time.

•Zimo Digital began developing a digital command control system in 1977 and launched it in 1979. The major difference in comparison with Hornby’s Zero-1 was that the Zimo system could control 99 trains and offered sixteen speed steps.

•Märklin Digital’s system, which appeared in 1984, was designed for use with Märklin’s line of Alternating Current three-rail HO locomotives. It was developed for Märklin by Lenz, using Motorola parts, hence the different mode and compatibility settings.

•The Trix Selectrix digital system appeared in 1982 and was designed for use with Trix’s Direct Current two-rail locomotives.

Controlling Speed and Direction

Traditionally, the speed and direction of a model train have been controlled by varying the voltage and polarity on the rails. The higher the voltage, the faster the locomotive moves; the lower the voltage, the slower the locomotive moves. If the right rail is positive with respect to the left rail, the locomotive moves forward; if it is negative, the locomotive moves in reverse.

Being able to control the speed and direction of a train is great, but controlling more than one at a time is even better. Over the years, modellers have come up with many ingenious methods to achieve this. The basic one has been block wiring, in which the model railway layout is divided up into electrical blocks, each of which can control one locomotive. A cab (or throttle) is used to control each train and arrays of selector switches connect each block. This method of control is also called cab control.

Probably the most ingenious method of cab control is also known as progressive cab control. As a train moves around the model railway, the connection between the cab and the block is automatically switched by relays to the next block, and the present block is released for another train to use. For a small layout, with one or two trains, block control is simple and straightforward to wire and instal. For bigger model railway layouts, however, the task can be immense.

The next evolutionary step is command control – a method of controlling individual locomotives (or trains) at the same time on the same rails.

The NMRA and the DCC Working Group

DCC has been around for many years in a range of formats, and today the main principles of the system are controlled by the NMRA so that everything is compatible. Before the 1930s, there were no common standards pertaining to any model railway equipment. Equipment supplied by one manufacturer would not necessarily work with that of another manufacturer, or even run on someone else’s track. In addition, because many modellers built to their own standard or from their own designs and ideas, it was difficult, if not impossible, to take a locomotive to another modeller’s railway and expect it to run without any issues. There were nearly as many couplers as there were manufacturers. It was a situation that was bound to be detrimental to the development of the hobby.

The National Model Railroad Association, or NMRA, came into being in 1935, when a gathering of model railroaders, manufacturers and publishers got together with the aim of bringing order to the chaos. The NMRA standards were developed to help ensure that equipment could be interchanged between one model railroad and another, and that carriages and locomotives of one manufacturer could run on the track of another manufacturer together with carriages and equipment of still other manufacturers and modellers.

Many of these basic standards have remained virtually unchanged from the time of their original publication in 1935. There have been some additions and refinements, but generally they have stood the test of time, proving to be of great benefit to model railroading. Their contribution to the development of the hobby to the point where it is today has been invaluable.

GE ASTRAC – a giant step forward in model railroading.

The first command control system was known as ASTRAC, developed by General Electric in 1964. As the electronics industry grew, new methods of controlling model trains were developed. Two of the most popular systems were Keller Engineering’s Onboard, and PSI’s Dynatrol, which both used audio tones to control each locomotive. Both systems worked well, but the user was still limited in the number of trains that could be controlled.

In 1978, Model Railroader magazine published a series of articles by Keith Gutierrez, the founder of CVP Products, giving readers instructions on how to build their own command and control system. Called the CTC-16, it could control up to sixteen different trains, all on the same track. Many other companies went on to use the same methodology to control 32 or 64 trains.

The problem with all the systems that were being developed and built was the lack of standardisation. There was no common ground between them (except for the CTC-16), so, in the late 1980s, the NMRA set up a DCC Working Group to investigate the establishment of a standard. Rather than reinvent the wheel, the group decided to study all commercially available command and control systems, along with proposals received from Keller and Märklin. Their conclusion was that the best system on which to base the new standard was one that had been invented by Lenz Elektronik, which was used at that time by Märklin for their 2-rail sets. This system offered the best signalling method electrically, as well as the fewest limitations on expansion. The working group expanded the design, allowing for control of ten thousand possible locomotives, points and multiple-unit consists.

The group’s revised standards were presented in 1993 and, by July 1994, they had been approved and adopted as the official NMRA DCC Standards. The finalised set of Recommended Practices was issued in 1995.

The DCC Working Group continues to clarify and expand the existing standards and recommended practices as the need arises – for example, with extensions such as Railcom.

2

DIGITAL COMMAND CONTROL

What Is Digital Command Control (DCC)?

In a nutshell, digital command control (also sometimes referred to as ‘digital command and control’) is a system, governed by a standard set by the NMRA, which offers the user the capability to run several trains at the same time, with the bonus of more simplified wiring.

Digital command control (DCC).

As soon as the command station is switched on, the track receives full voltage. Changes to driving speed and direction are made by sending a signal to the decoders in the locomotives, which in turn control the locomotives. The track voltage is effectively AC, so direction is no longer dependent on polarity. Locomotives will respond only to those commands that are directly addressed to them. With DCC, the locomotives are being controlled by the user and not via control of the track voltage (as was the case with analogue control). When using a DCC system, full voltage is supplied all the time the command station is switched on. A controller is used to send information to the command station, telling it what operation a particular locomotive should do. The command station then transforms this information into a stream of digital code and sends it as packets via the track to the decoder, which instructs the locomotive to carry out the instruction as requested. Rather like a digital television, the locomotive will respond only to signals that are addressed directly to it and will ignore all other signals.

The same process applies for accessories, which can also be controlled by a decoder. Accessory decoders can be used to control points, lighting, turntables, servos for crossing gates, and much more.

There are many different terms used in the realm of DCC; a glossary is included at the end of the book to help with understanding.

Basic DCC connections.

Choosing a System

When selecting a DCC system, asking a few questions will help you find your way around the range available:

•How many locomotives will be running at the same time?

•What gauge of locomotive will be run with the system?

•Will there be the control via DCC of points and/or signals to consider?

•Will computer control be required now or in the future?

•What power will be required for additional track-powered items, such as LEDs for carriage lighting, and so on.

The answers to these questions will point you towards identifying a system that will be the best fit. They can be used as a basis for discussions with a local retailer, who should be able to indicate what options are available, or for an online search. For more details on choosing a DCC system, seeChapter 8.

The Components of DCC

The basic requirements for a DCC system are a command station and handset, together with a suitable power supply. In addition, decoders will be needed for the locomotives. If points and signals are also to be controlled digitally, an accessory decoder will be required (seeChapter 11 for further details).

The choice of systems is wide-ranging, but, despite the many and varied opinions you will encounter among fellow modellers and journalists, there is no such thing as the ‘best’ one. The main advice should be to choose the system that you feel most comfortable with, and always try before you buy. All systems do the same thing, just in a slightly different manner.

Basic components for DCC.

As a user, it is essential to be comfortable with how the handset feels in the hand, and with the activation of the buttons, knobs, and so on. Basically, if there is anything about the system that does not feel good, running the layout will not be an enjoyable experience.

A DCC system can be made up of either a desktop command station with a power supply or a command station with a handset and power supply. Desktop units may also have handsets added to them if required.

Command Station

Command stations come in all shapes and sizes, some requiring a handset, some not. Some allow for the use of a smartphone or tablet as the handset.

DCC command stations.

Handset

Handsets also come in all shapes and sizes and can be added as required, as command stations are able to operate with multiple handsets. The user’s smartphone or tablet may also be used and, in some cases, can operate in conjunction with a DCC handset.

DCC handsets to go with the command stations.

Power Supply

One aspect of a DCC system that is often forgotten is the power supply. It must suit the system purchased and, of course, it needs to be appropriate for the country in which it is to be used. These days, many manufacturers will provide a suitable power supply for their systems. However, if this is not the case, it is essential to have the right information -- the maximum voltage the system will take and whether it will take DC or AC – so that you can choose the correct power supply or transformer for the system.

Power supplies and transformers.

Boosters

A booster for a DCC system is not a transformer or a power supply, but in principle an amplifier for the DCC signals from the command station. These are then combined with additional power output and the signals and power are sent to the track. Most DCC command stations come with boosters built in, and the total current output will be indicated in the manufacturer’s details. Additional boosters may be required at a later date, depending on a change in the current requirements of the layout. Should the total power required by the layout exceed that of the chosen DCC system, perhaps because the layout has developed and grown, then an additional booster can be added to the layout.

Boosters are responsible for converting the AC or DC power from the power supply into local DC power to the track. They are also responsible for converting the signals from the command station into packets of information to be sent to the locomotives.

Different boosters may offer various features: short-circuit protection, automatic circuit breaker function, regulated voltage provision and auto reversing. These are not essential but can be added bonuses for the layout.

Boosters can be beneficial to a layout if it is some-what more complicated or if it is being used for demonstration purposes, for example, at a club or exhibition. For the average home layout, however, a booster is not necessarily required, especially if best practices are followed for the wiring and the system has sufficient current for its running requirements.

Decoder

The next component required is a decoder for the locomotive, if it is not already fitted with one. Again, there are many makes, with different sizes and capabilities. To decide which is the best one for your requirements, ask yourself the following questions:

•Is it just for control of the locomotive or is sound going to be wanted too?

•What is the current draw of the locomotive?

•Will there be a need to have operational lights on the locomotive? If yes, how many?

•Is the locomotive DCC-ready? If so, what socket does it have fitted?

•What space is there in the locomotive for a decoder? If sound is going to be fitted, then it is essential to consider the space required for the speaker too.

Some manufacturers may specify a particular decoder to be used in their locomotives. Although this is useful information for the user, it may be the case that a third-party decoder offers more features.

For more on decoder choices, seeChapter 9.

Accessory Decoder

The final optional component is an accessory decoder, which will allow for the digital operation of points, signals, lights, and much more.

Accessory decoders are normally multi-output units that are mounted under the layout in a stationary position. They can be used to control points/turnouts, structure lights, scene lights, animation, signals, and other items that require an on/off signal. They may or may not provide power to the accessory.

Anatomy of a Peco turnout/point.

As with everything else, accessory decoders come in a variety of shapes, sizes and outputs. They are usually multifunctional; however, when considering them for control of points, it is very important to know what point motors are being used. There are specific modules for solenoid (snap-action) point motors and for slow-action (stall motor) motors, as well as for servo motors.

Points (also known as turnouts and switches) are movable sections of track that allow a train to move from one line to another, guiding the wheels towards either the straight or the diverging track. In the model railway arena, points are used to change the direction of travel. They are typically made from metal and plastic and can be operated manually or by a point motor. The most important thing to remember when using points is that they must be correctly aligned with the track.

The term ‘turnout’ may be used to describe a point in some instances, but it is actually a combination of a number of components, only one of which is the actual point. The component known as the point is the short section of rail that physically moves to direct the train one way or the other. It is often referred to in model form as the ‘point blades’.

There can be many components to a DCC system, but only the command station, handset (if there is one), power supply and locomotive decoder are essential. All other items are optional.

3

COMMON MISCONCEPTIONS AND MYTHS

There are many misconceptions and myths around regarding DCC. Some of them are relevant and others are not. The main advice is always to ask as many questions as possible when starting out and do not believe everything you hear.

Misconceptions

‘It’s Expensive’

The thinking is that this type of control must be costly, even for the most basic system, but this is not necessarily the case. It is possible to start with a set-up that will do everything needed to control locomotives and even accessories for around £200. It is true, however, that a digital system that can control multiple locomotives at the same time, which will require either a multi-channel DC controller or individual controllers for each track, may cost less than a comparable analogue DC system. There are also continuous costs for locomotives that are to be run on a DCC layout, as they will all need decoders. A locomotive with no decoder fitted will not run on a DCC layout; it will just sit there and hum, with the motor oscillating very quickly. There are some systems that will allow the running of an analogue locomotive on Address 0, but these permit the user to control speed only. Again, the locomotive may produce a hum from the motor.

‘It’s Difficult’

There is a belief that you need to have a deep understanding of computers and computing. This is not the case at all. Setting up the command control system is fairly easy: two wires from the track to the command station, and two wires for power into the command, and everything is ready to go. The most difficult aspect is adjusting to a system that is different from the old DC one and learning how to control multiple locomotives at the same time. Although DCC systems are based on computer technology, there is no need to be an expert or even know anything about computers. However, although the actual use of the DCC system is very simple, installing decoders into the locomotive could present more of a challenge, especially in N gauge, and require some electrical knowledge. SeeChapter 10 for further information.

‘It’s Intimidating’

Some people believe that DCC systems are too sophisticated and have too many buttons. They do come in all shapes and sizes, so a newcomer to the hobby may find them intimidating. Reading through the manuals – which have usually been written by technical engineers – can also be quite confusing. It is usually best to have a quick initial read-through, then go away and have a cup of tea before having a more detailed look. Most manufacturers also supply a ‘quick-start guide’ on running locomotives, and in principle it should be very simple to get going by following this. As progress is made and the need to delve deeper into the capabilities of the system arises, you can then sit down and read through the manual in detail or consider attending a course or workshop.

DCC is actually a true ‘plug-and-play’ product, which does what it says on the tin. Using it requires no special skills and it is ready to go straight out of the box.

It’s a Niche Area of the Hobby

Command control has been around for over 40 years, and various versions of DCC have been available for over 20 years, but there are still some people who believe that it will never catch on! More and more layouts on the exhibition circuit are now being run using DCC, giving visitors the opportunity to see the systems in action. As DCC becomes increasingly familiar and more popular, hobbyists are seeing the benefits of using it on their own layouts and getting into the DCC scene.

As with everything, DCC is not for everyone. Everyone has their own likes and dislikes and ways of doing things. Deciding to use DCC is a personal choice and as such everyone can make up their own mind as to what is best for them, once all the facts are to hand. Again, it may be worthwhile considering attending a course/workshop to get a better understanding on what it is all about.

Myths: True or False?

There are many myths and beliefs surrounding the different elements of DCC control; some are partly true, some are partly false, and some are just plain wrong!

Signals

DCC track signal is AC or DC

Partly FALSE. Although it is like AC, it is actually neither AC nor DC. DCC is digital data sent in the form of pulse width modulation (PWM) on the rails. If the signal were to be looked at through an oscilloscope, a square wave would be seen.

DCC uses a carrier signal

FALSE. DCC does not use any carrier signals to transmit information. It is purely digital.

DCC uses DC with a signal riding on top to control the locomotive

FALSE. The DCC signal on the track is composed of both power and data. The signal is an AC-like digital waveform of a suitable amplitude to power the locomotives.

DCC square wave as seen through an oscilloscope.

The DCC signal is a low-frequency square wave with a high-frequency control signal

FALSE. The DCC waveform is both power and data, where the binary data is encoded in the form of long (100µSecond) or short (58µS) pulses. The DCC signal will vary between 5000 and 9000 Hertz (Hz) because of the pulse widths switching between those two states.

The DCC signal has polarity

FALSE. There is no concept of polarity with DCC. DCC is phased. A phase mismatch causes a short-circuit. The NMRA’s DCC Standard states that the rail considered positive is impossible to define, so, when talking about wiring, the rails are referred to as right and left or red (+ve) and black (-ve).

DCC uses a differential signal on the rails

FALSE. While the NMRA DCC Standard describes the signal as a differential signal with no ground, this is a description only of what the waveform looks like on an oscilloscope, not of the signals themselves. Differential signalling requires two complementary signals, which are then summed to eliminate/reduce noise-induced errors when using high-speed communications between devices. As DCC uses a much higher voltage with a much slower data rate, it is much less susceptible to noise. The DCC protocol also includes error detection.

Voltages

There are positive and negative voltages on the track

FALSE. On a DCC track there are only positive voltages present. The phase of the rails does not control the direction as with analogue, hence there is no polarity. This then means that there are only two possible states: high or low.

DCC needs a negative voltage to reverse direction

FALSE. The multifunction decoder determines the direction, not the track voltage. Motor control is achieved by the switching sequence of the motor circuit.

DCC voltages can be correctly read with a multimeter

FALSE. Only a purpose-built DCC meter such as the RRamp meter or an oscilloscope will give accurate readings. This is also true for a true RMS meter. A regular digital meter set to AC volts will give only an approximate voltage.

Wiring

Analogue and DCC can be run on the same layout

FALSE. When direct current and DCC meet, only bad things can happen. If it is necessary to use analogue power, the layout can be wired so that only one source of power can be connected to the layout at any one time.

Only two wires are needed for DCC Technically TRUE but in practice FALSE. Although DCC eliminates much of the wiring that was needed for analogue operations, and a very simple layout can be run quite happily with only two wires, it is not recommended.

Terminators must but used if the track bus is long

FALSE. Most DCC manufacturers do not insist on or recommend terminators. The track signals should be checked first to determine if there is a problem, which may require a different solution. Many signal integrity issues are directly related to inadequate wiring. Where there are very long lengths of wire, it may be advisable to twist the wires every so often to avoid interference.

Boosters

Boosters are brand-specific

FALSE. Many boosters can be interfaced to a different brand of command station. Most boosters have a low voltage or logic level input, while some can work with track voltage. The myth comes from the fact that it can be a bit of a challenge to determine precisely how to connect it. If, however, there is any doubt about connecting a booster correctly when adding it to a layout, it is advisable to use the same brand as the system.

DCC will not work without the addition of costly boosters

FALSE. Additional boosters provide additional power, as required, but are not always essential. Typically, a DCC system will include a built-in booster.

Larger layouts need additional boosters

FALSE. The number of boosters required is based on the power consumption, which depends on several factors. How many locomotives are running at the same time? Do they have sound or lights? Are lighted passenger carriages being run on the layout? Are there accessory decoders on the track bus? Has best practice been used in wiring the layout?

The boosters with higher current ratings are better

FALSE. An oversized booster will have too much available inrush current for smaller gauges, which could cause damage to a locomotive, unless circuit protection has been set correctly. If a power management device has been employed and the layout has been divided into power districts, with a lower current setting (for example, 4A), this may make sense. A high-current booster can deliver a significant amount of current into a circuit – as much as 60A for a brief period – which could result in damage before a circuit breaker has the chance to react to it.

The command station will shut down when a booster is shorted

MAYBE. If there is only one command station with a built-in booster and no circuit breaker at all, then this can happen. The protection in any booster or command station is designed to protect only the equipment of which it is a part. Other standalone boosters will continue as if nothing is wrong.

The exception to this rule is the NCE Power Cab. Unfortunately, due to its integrated design, a short will cause the entire unit to reboot. For this reason, NCE offers a protection module called the CP6, which has the role of limiting the current and preventing a reboot.

Decoders

Sound decoders need a lot more power

FALSE. High inrush current occurs only at cold start-up. Otherwise, sound only needs about 20% more power than a motor decoder. Adding an energy storage device to any decoder will also increase the inrush current.

BEMF (back electro motive force) never works in a consist

Not an absolute TRUE/FALSE situation. BEMF is sensitive to mismatches of decoder, locomotive or manufacturer and can be difficult to set up correctly. However, it can be done. Most users do not need BEMF, and it is acceptable to disable it if it is causing issues. Some multifunction decoders will disable BEMF when in a consist.

Programming on the main (OPS mode) is dangerous