TIPS & TECHNIQUES

 
 
I have not yet ventured into the world of DCC. I have read a lot, and am still evaluating the pros and cons.
 
If you are new to DCC and are wondering what it is all about, this article is for you. It is aimed towards someone that knows nothing about DCC and is intended to answer some basic questions you may have about DCC.
 
DCC Vs DC for model train control what is the difference?  There are some big differences between the methods, but many of the fundamentals are still the same. The small details are the cause of all the discussion, confusion and problems for some users.
DCC stands for Digital Command Control. It is a system where digital commands are sent to the locomotives through the rails. The layouts of yesteryear used block control. Each required its own power pack and a complex control panel to keep each locomotive electrically separate from each other. DCC allows independent control of multiple locomotives within the same block.
DCC provides for digital control of turnouts and signaling as well. Other features include a multitude of sounds, block detection, momentum control, and the ability to lash together several locomotives.
DCC is an NMRA standard. This means locomotives equipped with decoders from various manufacturers may be used with any DCC system!
A DCC system consists of five basic components. Most starter sets come with everything you need except a decoder. (Some may require you to buy your own power supply.)
Command Station - The heart or brains of DCC. The Command Station is a dedicated computer-like device that communicates with all the other parts of the DCC system. Selecting the brand and model of Command Station is key to selecting the type of Throttle controls as well as future expandability of the system.
Throttle or Cab - The interface between You, the engineer, and the Command Station controlling the train. Various Throttle equipment styles exist. Some systems use a plug-in, walk-around Throttle, with the possibility that more than one can be used at the same time. Some systems have Throttles built into the Command Station. Some are totally wireless. Each brand of DCC system requires their own brand of Throttle or Engineer's Cab, and their specific type of Throttle to Command Station wiring interface. You cannot easily intermix brands here.
 
Booster - A power amplifier of the communication signals from the Command Station into power applied to the track. Some starter systems combine a Command Station and Booster into one box. Almost all Boosters require an external Power Supply. The ampere rating of the Booster and Power Supply will limit how many locos you can run at the same time. Some Boosters are in a separately available box and may be controllable from some Command Stations of a different brand.
Power Supply - An AC transformer or DC power source for the Command Station and track power Booster. The Power Supply is NOT INCLUDED with many DCC equipment systems and must be purchased separately. An additional Power Supply is usually required with each additional Booster.
Loco Decoder - An electronic receiver inside the loco out on the track. The Decoder receives communications from the Command Station and controls the loco motor and lighting effects. Some Decoders also add locomotive sound operation. Every DCC controlled locomotive must have its own decoder. But any brand of Loco decoder should work with any brand of DCC Command Station / Throttle equipment.
Many home layouts are easily accommodated with starter systems that include the above basic items, plus a few additional Loco Decoders. [But be sure to ask about the Power Supply.] However, as your model railroad grows you may want more DCC equipment, including: additional Throttles for multiple users (same brand); remote Plug-In panels for walk-around Throttles; Accessory Decoders for DCC operation of track switches (turnouts); Auto-Reversing track controllers; more Power Supplies & Boosters; Electronic Circuit Breakers for separation of track circuits into multiple power districts; or even Radio equipped Throttle Adapters.
Note that a personal computer is NOT required. Computers are only needed for signaling or a few of the do-it-yourself DCC systems. NONE of the commercial systems require a computer and therefore, no programming is required. The only thing you need to do is configure the address of your locomotives.
Some of you have been out of model railroading for a number of years. Maybe you were raising children. You are finding that there are significant changes that have occurred since the last time you ran a train. These are not just changes, they are improvements! You will find that you can run trains like you never have before. They have sound now and some smoke. The detail is better and they are better running. Welcome to the new and improved world of DCC trains! Still, you are a little overwhelmed.
First, to avoid having to learn about electronics, buy a starter set that has everything you need. That way you don't have to learn about the various components of a DCC system. You will know you have everything you need
Just be aware that some starter sets need a transformer. Your dealer will be able to tell you if you need a transformer and sell you one. Transformers today come complete in housing with a plug. Just attach the two wires from the transformer to the input terminals on your starter set and you are ready to go.
Unless money is really tight for you, buy a starter set that has all the capability you need. There are some introductory systems that are expandable. Get one of them if you can't afford a full-featured system to start.
Second, buy a locomotive that is DCC-ready and then add a drop in decoder. This will get you into DCC without having to be a wiring and electronics expert. Again, your dealer will be able to recommend a locomotive and the right decoder to match your budget.
Third, wire up some track. Make sure everything works.
Those that switch to DCC from a traditional DC layout and have a fleet of DC locomotives often contemplate a layout that combines DC and DCC.  The fear is that you can't afford to convert all those locomotives.  Don't worry about it.  Go ahead and jump into DCC!  There are some good reasons.
I will start with the bad news.  Mixing DC and DCC can be fatal to your DCC electronics.  If a locomotive crosses a gap between a segment on DCC and another on DC, it could fry things.  If you have a crossing that has one side DC and the other DCC and a locomotive derails on it, smoke could be the result!
For standard DC controls, the 'throttle' puts variable voltage power on the track. Loco motors and headlights connect directly to the track. The speed (and intensity of the lights) will vary by simply changing the voltage applied to the track. Electrical current (amperes) drawn by the loco flows through the track rails and feeder wires. More than one loco can be operated on the same rails when coupling them together (mu'ed) but since they all receive power through the same throttle, they will all run at the same speed (when geared the same). If you want to operate more than one train independently of another, you must break up your layout into multiple control blocks (power districts) where each has its own operator and throttle.  Furthermore, since an operator is watching the trains and controlling the throttle, he often adjusts the track voltage setting to get to the desired running speed. This unconsciously compensates for all kinds of electrical sins that cause problems with DCC. (Poor electrical connections, resistance in the track rails and feeder wires, power supply sag with load, etc. etc.)
DCC puts 'fixed' electrical power on the track. There is a special receiver (the decoder) inside each loco that receives track power AND listens to commands sent out over the rails from a master control  (command station). These gadgets are actually small dedicated computers and electronic hardware. The DCC track voltage is an amplified computer to computer serial communication link bit stream, manipulated by the control station and beefed up by the 'booster' to have enough power to operate motors and lights out at the train. The whole reason for DCC is to allow multiple locos to operate independently on the same track, without having to divide up the layout into complicated electrical control blocks. The DCC communication scheme allows this to happen. Power for operating the locos still must come from the track, but all of the track can now be electrified in unison. This does simplify track wiring on most layouts. However, power from the DCC booster must be able to reach and operate all the moving locos simultaneously. This means that track wiring for DCC may need to be more robust than that for DC.
Since all loco power must come from the track and more than one loco may be running, DCC boosters (and their power supplies) are designed to have current ratings of 5 to 10 amperes (amps) or more. Most traditional DC power packs are meant to run only one train at a time. But since DCC locos and their ampere demand may be located anywhere on the layout, wiring to the track for DCC should be designed to handle a higher number of amps. There are two primary reasons for this. For all locos to operate independently, the voltage signal on the track should remain fairly constant in magnitude and not subject to sagging as a train moves around the layout. This becomes important specifically with larger layouts when a second, third or fourth train also drawing 1 or 2 amps may be in the same vicinity. Voltage sag caused by electrical resistance of the track or track feeder wiring should be avoided by having more track feeder wire connections scattered about the layout and using heavier gage wire than that required for simple DC systems. A second reason for a more robust wiring system is to ensure that the over current protective devices built into the DCC booster will indeed operate correctly. This is necessary to protect your model railroad equipment from damage caused by an accidental electrical problem. With simple DC the relatively puny power packs are limited to 12 volts times 2 amps or about 24 watts of power. Since you are probably operating only one train at a time, it is relatively easy to observe that the train stops when a derailment causes an electrical problem, and turn off the throttle while fixing it. With DCC, a booster can supply 12 volts at 5, 8 or even 10 amps into a track short circuit without becoming overloaded. That represents perhaps 60 or more continuous watts being available to cause spot heating at the source of an electrical problem. This can easily burn out wires inside the locomotive decoder, pit metal wheels or melt plastic track ties. The cure is to make sure that a short circuit at the track, regardless of where it occurs, can draw enough instantaneous current to cause the booster to shut down. Designing the electrical distribution system for low resistance is about the only way to resolve either of the above issues. This generally means larger wire, solid electrical connections, soldered rail joiners and more track feeder drops to avoid the inherent electrical resistance of the rails. The much discussed DCC bus distribution system helps to do just that. A practical criteria is to ensure that a piece of metal placed across the rails will always cause track power to be disconnected, anywhere and everywhere on the layout. One of the additional techniques used on club sized layouts to avoid the nuisance of having the whole layout shut down when only one operator has a derailment is to break up the track into smaller "power districts" each protected by an electronic circuit breaker. DCC auto-reversers are also available to quickly detect a momentary short circuit and re-connect track polarity to a reversing track section. For either of these to be effective the protective circuit breaker must trip on an overload, or the auto-reverser must re-orient track polarity, faster than the main layout booster will trip. Again, a low resistance track circuit helps allow that to happen.
Another complication is that the DCC voltage on the rails is AC rather than DC. However, this is not quite the same as the smooth cycle constant low frequency 50/60 Hz AC available at the local utility wall outlet. The command station to loco communication scheme relies on relatively fast reversals of track voltage to be detected at the loco decoder. It is the timing of these transitions that form the serial bit stream of computer to computer communications. If the decoder in the loco cannot correctly read the commands, DCC does not work. This means that short power interruptions to the loco caused by poor electrical connections or dirty track previously ignored by DC throttle systems can cause major havoc with DCC. Another subtle difference becomes important on larger layouts. As power wiring between booster and track becomes longer than 30-40 feet, the inductance of track power wiring can become more significant than the electrical resistance. A track voltage loss and voltage 'ringing' occurs as the DCC signaling scheme attempts to quickly reverse track voltage. This causes a voltage drop at the track and possible loss of DCC signaling even though the measured DC resistance of the wiring may be low. Using a larger wire gage on the DCC bus or track feeders does not necessarily help this problem. Twisting the DCC bus wires to lower the inductance, or moving the booster to utilize shorter wiring runs, or providing another booster closer to the track will help.
Blocks
Theoretically, you do not need blocks as in the traditional sense. You will need blocks if you are using block detection or polarity reversing sections such as wyes, balloon tracks, and turntables.
While you don't need any more blocks than this, if you have a layout that will be operated by more than one person, it is recommended that you install additional blocks to ease troubleshooting. You don't need as many as you had with a traditional DC-powered layout, but without at least a few blocks, you will not know where to start if you have a problem. Furthermore, if you have a short on a DCC layout, the whole layout may shut down without blocks.
The only thing that the NMRA made standard was the DCC signal on the track. That means all locomotive decoders as well as stationary decoders for controlling turnouts and signals are interchangeable. You can use any of these devices with any DCC system that supports the use of such devices. (Some starter systems do not support turnouts and signals.)
Some boosters are interchangeable with command stations of a different manufacturer. I'm not sure why you would want to do this. If you think you will be saving money, just keep in mind if it doesn't work, you might have trouble getting help from the manufacturer of either system or others on the Internet. To ensure you don't have any problems, you should stick with boosters made by the same manufacturer as your command station.
In general, throttles are not interchangeable with command stations manufactured by someone else.
The best DCC system is the one that works best for you.
When selecting a system, especially a starter system, make sure it has the features you want. If you want sound, make sure the system supports functions that will trigger your sounds. You will want to use your locomotive number as its address, so make sure you get a system that supports long addressing. Does it support consisting? Can it control turnouts? Will the system be able to grow with your needs or is it not expandable?
If you have an existing layout, you may be able to use it as is. Most of the advice given in this article is aimed at giving you trouble-free operation. Minor problems that you tolerate with DC may give you major problems with DCC. This is for two reasons. One, if you have multiple operators, a minor problem may affect all operators simultaneously giving you major headaches. This might happen when your booster shuts down. The second reason is that DCC systems are capable of putting much more current onto your track. This can cause melted plastic parts and pitting of your track and wheels from arcing.
The most important thing you need to do to determine if you can use your existing wiring is to hook up your booster and give your entire layout the "short test."  When running this test, flip all your turnouts. All the manufacturers insist that your layout be able to pass this test. Being able to pass this test will avoid melting and arcing If you have a wye, a balloon track, or a track plan that loops back on itself, you will have a short circuit. In order to deal with this situation, you will need some way to avoid the short circuit. This is accomplished by designating a section of track as the reversing section and you will usually need an automatic reverse section controller or simply call it a reverser. In addition to needing a reverser, you will need to use insulated joiners at both ends of your reversing section.
If you have a turntable, you will also need a reverser. If you have a balloon track, you may be able to use a relay which is less expensive than a reverser.
Whether you use a relay or a reverser, they are pretty simple to hook up. Usually two wires feed the reverser from the mainline or non-reversing track. The reverser then feeds the reversing section by two wires.
DCC can control turnouts.
You can even have the turnouts report the turnout status to a central computer. You can use this to operate signals or control train movements.
You can control your turnouts with push buttons or from your throttle.
Sound
You can have all sorts of sounds! While DCC is not required to have great sound, great sound arrived shortly after DCC. DCC does provide for the control of sound that previously wasn't possible. You can control the whistle, bell, dynamo, blow down, coupler clanking, horns, dynamic breaks, and the diesel engine. Plus you get the fireman shoveling coal, air compressor, oiling and more.
CV is short for Configuration Variable and these are the decoder's microcontroller adjustable parameters that are used to determine how the decoder's outputs (motor, lights etc) perform and setting its address. Once a CV is adjusted it is remembered even when power is removed. A few examples are the address, CV 1 - short and CV 17 & 18 - long address and CV 2 that is used to set the first (start) speed step. All decoders have the basic operating CVs and other CVs that may be unique to that decoder. Refer to decoder's instruction manual for all associated Configuration Variables.
 
Adjusting the CVs is what the DCC manufacturers call programming (bad term, makes DCC sound difficult like computers and it isn't) is usually done by giving a decimal value between 0 and 255 for most CVs; see your owner's manual.
 
The manufacturer has entered default values for each CV that enables the decoder to run a loco without any adjustment (programming). To address this decoder you must select "3" the default value for CV 1, the short address. The decoder can be reset to default values. For independently running of locos, all locos decoders must have unique addresses.
Momentum is available with DCC.
You get two flavors. The standard DCC decoder in each loco has separate settings for acceleration and deceleration rates that allow you to easily simulate the slow starting and stopping action of a fully loaded freight train or the faster throttle-brake response of an unloaded switch engine. The NMRA has identified adjustments for this feature at CVs 3 and 4. However, each decoder manufacturer may interpret the meaning of a specific numeric setting in their own way, so different brands and models of decoders may not operate the same way in all (14, 28, 128) throttle step modes. The user must determine the ideal setting for a given engine - decoder - load combination.
Another momentum-like feature is that most DCC systems will allow the user to select a loco, get it moving, and keep it running at the same speed setting indefinitely while the cab throttle is unplugged or a different loco is selected and operated from the same cab. The throttle "memory" is ideal for following a train around a plug-in walk-around layout.
DCC Ready, as used by Bachmann in their G-scale locomotives, means something different. It simply means that it will be less work to install a decoder than if they had not made it "DCC Ready." But it still may be a lot of work. For an example of a Bachmann DCC Ready locomotive, consider the installation instructions for their external-frame Consolidation. If you are new to DCC and not confident of your wiring ability, you may not want to tackle a Bachmann as your first project. Bachmann provides no instructions other than "see the instructions for your decoder" - which are obviously generic. For specific instructions, see this and other websites. I have not worked on any other G-scale locomotives claiming to be DCC Ready to know how DCC Ready they are.
I don't mean to scare you, okay, maybe a little bit, but not all locomotives that claim to be DCC-ready are. In fact, some are wired wrong and could damage your decoder. Okay, there is that scary thing again. The sad fact appears to be that model train manufacturers don't employ electrical engineers nor do they try out their "DCC-ready" locomotive with a DCC decoder before going into production and selling it to you. Sometimes it is as simple as no decoder will fit in the space provided. Worse, your decoder could be damaged. Do one of the following:
Capacitors on Motors
In general, if your locomotive has "EMI" capacitors across the motor, these should be removed if installing a decoder. Especially decoders utilizing "back EMF" won't work with these capacitors.
Even locomotives that are alleged to be DCC ready, if they have capacitors, you may have to remove them. Remember, many manufacturers don't test their DCC ready locos.
You can try your locomotive with the capacitors, but if your decoder acts funny, stop and remove them. The capacitors are intended to reduce radio interference. So if you remove them, you might have radio interference with a TV, your cell phone, or your wireless throttles. But I think the chances of that happening are unlikely.
If you think you have interference with a loco that has the capacitors removed, you will not have interference from a stationary locomotive or one that is removed from the track. If your throttle or whatever is still acting funny, your trouble is somewhere else.
To operate the motor in the loco, the decoder has to provide a varying voltage from min to max value. In 14 speed steps there are only 14 different values of voltage, 28 has 28 values and 128 has 128 values. These values are called speed steps. Depending on the type of decoder some speed steps can be adjusted to modify a linear speed curve. Options on some decoders for speed step adjustment (speed tables) can be volts Start, volts Mid and volts Max, internal user selectable speed tables, manual adjust of speed steps CV 67 - 94 for 28 speed steps and external computer adjustment to these CVs to adjust motor performance, to enhance loco especially slow speed operation and to match different mechanisms to have the same performance.
14 speed step decoders are basic early units and may cause jerky motor operation.
Decoders have a few CVs that can be adjusted to fine tune the motor performance, especially better slow speed control. The basic adjustment of CV 2 is Volts Start. Adjusting this enables the loco to start moving at the first speed step. Adjusting CV 5 (volts max) will reduce maximum speed and adjusting CV 6 (volts medium) will now change the linear voltage table to non linear, that is reducing the value of CV 6 will give smaller increases in speed in the first half of throttle rotation, (flatter speed line). Later model decoders have the added feature of dither, torque compensation or back EMF (manufacturers names) to further improve slow speed control, by modifying the pulses of current to the motor to overcome inertia and mechanism friction.
Some decoders have selectable speed tables that have their speed steps in such a manner to alter the linear speed table to have more or less throttle travel at low or high speeds, refer decoder instruction manuals. When a speed table has small increments at the low end and larger increments at the high end, this makes for better low speed control. Speed tables can also be manually loaded or the use of a computer with a program like Decoder Pro connected to the command station.
The use of speed tables and CV2, CV5 and CV6 enables you to speed match locos to perform the same, irrespective of the mechanism. Some sound decoders do not support CV5 and CV6.
I don't intend to have many locomotives. Why might I want long addressing?
It's not a matter of how many locos you have. Long (4 digit) addressing is used so that users can address their locos by its road number. If you had a loco with a road number of 5305, using the short (2 digit) address you have to
remember which of the two digits to use, and visitors would have a bigger problem. It is easy to address any loco. Just use the actual road number.
Back EMF (electromotive force) is a feedback method used by some decoder manufacturers to provide a constant speed of the loco irrespective of grade of the track or load without adjusting throttle. This is a form of "cruise control" for locos.
Therefore when the train comes to a hill it would maintain the same speed going up the hill as on the flat.
How many trains can a throttle control?
 
This depends on the throttle. You will have to look at the manufacturer's literature or website. One or two is typical. Some throttles and systems support consisting. This allows several locomotives to act like one and thus, counts as one
 
Selecting a decoder is fairly easy. The main thing is to find a decoder that fits in your locomotive. If your locomotive has a decoder socket, as many newer models do, you will want a decoder with a plug on it. Make sure the decoder has the features you want. Unless you buy a budget-minded decoder, most decoders will have the features you need like four-digit addressing.
There are many features a decoder can have. I could describe them here, but that may not help you in determining what you need. You may not know what you need or want. To make things simple, don't buy a budget-minded decoder and buy one that fits with a plug on it if you need it. As you learn about what features are desirable, a non-budget-minded decoder will likely have what you need.
One more thing. Many locomotives, particularly diesels, have decoders made just for your particular model. Diesels are tight for space so DCC manufacturers are providing decoders just for the particular model you have. Check your favorite DCC manufacturer's website and see if they have a decoder just for you.
 
 
A QUICK LOOK AT DCC
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