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DCC Frequently Asked Questions
Last updated 29 April, 2013
Last updated 29 April, 2013
 
This page was last updated 29 April, 2013
 
We are developing this page in response to a large number of customers who feel that such a page would be of help to them and others who are starting in the world of DCC. If you have any additional questions you would like answered or have contributions to make to existing answers below, please email us here.
Click on one of the following to take you straight to that section, or just browse the complete set of questions and answers.............

About DCC/Which system should I get?

Wiring and Feedback

Track and points

Decoders

CVs

Lighting

 
Area

Q. What does "DCC" stand for?

A. Digital Command Control

System

Q. What is the difference between DC and DCC?

A. With a DC (analogue) system you apply power to the track when you want to move a locomotive. With a DCC system all of the track is live all of the time, so you can drive more than one train at a time on the same track. This does have its problems! There are ways around these problems, though, as you will see below. Each locomotive is controlled by the use of a decoder. This device allows additional features such as sound and lighting to be controlled through the electronic pulses that travel through the rails. In addition you can control points and signals from the DCC controller, or from a computer if you want to link the system into a PC.

System

Q. What is DCC all about and how does it differ from DC?

A. Click here for a presentation which summarises the main points about the basics of DCC, and lots of other information about using DCC One of the main advantages is the ability of controlling more than one loco on the same piece of track, either by the same operator or with two or more operators. You could, for example, realistically simulate banking, as shown in this video clip.

System

Q. Can I use DC and DCC on the same layout?

A. In theory it is possible and there are some modellers who have set up this arrangement. However, DC and DCC do not talk to each other as they use different types of electrical supply so advice would be to avoid this setup if at all possible.

System

Q. Which DCC system is best for me?

A. Unfortunately there is no right answer to this question. The best system is the one that is right for you. The only way to find that out is to do some research and look at what systems are around and what features they have. Try them out if at all possible by going to shops, shows and/or fellow modellers but beware of the person who says that the only DCC system you should buy is the one they have! Also beware of retailers who only recommend systems from the main UK model railway manufacturers. There are many (and better) systems from a wide range of other companies. Don't necessarily buy cheap - it could cost you more in the long term as you may well outgrow a basic system very quickly and want to upgrade - cheap basic systems are not generally upgradeable so this will result in a completely new purchase and a loss of investment. Wherever you live you also consider what support is available locally for the system you buy.

System

Q. What should I look for in a DCC system?

A. Again, much of this is down to personal preference as well as looking for a system that will not only satisfy your needs now but can be expanded at some later stage to take into account further developments. Remember DCC is changing rapidly and new technologies will be increasingly used so it is important that systems are upgradeable. All model railway layouts are developing in some way. Look at how easy a system is to use and handle - is it user friendly? Will it handle all of my locos, i.e. does it provide enough power? A 5 Amp system is probably more than adequate for the average user and there are many lower powered systems that are suitable for those starting out in DCC. Do I want to control points, signals and other accessories with the system? Do I want to connect a computer to the system, either for controlling the layout or for programming locos?

System

Q. What is a command station?

A. This is the control centre of the system through which all of the commands from CABS are sent to the devices you are controlling.

System

Q. What is a CAB?

A. Not something you would find in a bus! Sometimes called a throttle, the CAB is the device from which you control the locos and other accessories on your layout. It is also the device that is normally used to program decoders, though not all cabs can be used for this purpose. With many systems you can have a number of cabs around the layout, connected together with the COMMAND STATION via a BUS.

System

Q. Can I use radio to control my DCC layout in the UK?

A. Yes, provided the system uses a radio wavelength that is compliant with EU legislation. DCC systems manufactured in the US are generally NOT compliant and cannot be legally used in the UK - it would also be foolish to do so as the wavelengths used by some US systems conflict with mobile phone or air traffic control wavelengths here in the UK.

System

Q. I have the NCE PowerCab. Can I show the amps being drawn on the layout?

A. Yes, there is an option to change the time display to amps. To change the display, press the ESC key repeatedly until you get to SET CAB PARAMS. Press ENTER. The first option will ask if you want to display Track Current. Press 1 for YES. When you get to the next option press ESC to take you back to the operating screen and you should now find that the number of amps being drawn by your layout is shown top right hand corner of the screen.

System

Q. What is consisting?

A. Consisting is a term that originated in the US to describe a multi-headed train, using two or more locos. Most quality DCC systems allow the creation of consists. However, once you have added locos to a consist it is important to remember to remove them as well or else you run the risk of having a loco (or locos) permanently assigned to a particular consist and you will lose the ability to control them individually.

System

Q. What is a decoder?

A. A decoder is an electronic device which you need to install to operate devices, such as locos, point motors, signals and other accessories. Each locomotive needs its own decoder as it stores the loco number, used to call up and operate the loco, as well as other settings that apply to that loco. These other settings can control, for example, the maximum speed of the loco, light settings, sound settings and settings for any other add-ons that the loco might have. There are also accessory decoders that are used to control things such as points and signals. These are not the same as loco decoders, so make sure you order the right type! Many accessory decoders look the same as loco decoders. Click here for more information about decoders.

Decoders

Q. How do I know which loco decoder I need to install?

A. Decoders to control the motor inside a loco come in various sizes. You would be well advised to look inside the loco to see how much space there is. Steam locos in particular do not have much space inside for a decoder. You also need to see what the stall current is, i.e. how many amps are being drawn by the loco when the motor is stalled on the track? Most standard decoders have a stall current of about 2 amps. You also need to check that the decoder has sufficient output to control the motor in the loco you want to use - for example, you CANNOT use the R8215 Hornby decoder in some Heljan locos as the locos have a greater power requirement than the output of the decoder. One other factor you will need to take into account is how many functions you want in order to be able to operate the loco and all of its installed features, such as lights. Many modellers find that for a standard OO steam loco a 2-function decoder is adequate. However, for a DMU, for example, you might want a 4 or 6 function decoder in order to be able to control individual lights front and rear and any other lights that you might have fitted. If you want install a sound decoder you need to check that the decoder is of the right type for the loco.

Decoders

Q. How do I program a decoder?

A. Click here for a guide to programming decoders.

Decoders

Q. Can two loco decoders have the same loco address?

A. Put simply - YES. However, the two locos will be treated as one by the system so you you probably wouldn't want to do this in practice. If you want double heading (called consisting) this can be achieved in other ways. You might, though, want to have decoders in different carriages of a DMU with the same loco number so that they are treated as one. This makes the control of lights, etc. much easier.

Decoders

Q. What is a function only decoder?

A. A function only decoder is not able to control the loco motor but will be able to control things such as lights or smoke units. In a DMU, for example, you would want a standard decoder in the carriage with the motor but you could use function only decoders in the other carriages where you might want to control lighting features. You need to check that the decoder has sufficient output to control the physical device you want to use. Some function only decoders can only be programmed if there is a current load, so programming a function only and motor decoder together would be one way of doing this. See an example of how to do this here.

Decoders

Q. Can I map functions to particular buttons on my controller?

A. Yes, but this will depend on the decoder in use. You will need to consult the instructions that came with the decoder to find out which CVs you need to change. For remapping of functions on TCS decoders, for example, see their Simple Programming Guide here.

Decoders

Q. Do I need to remove capacitors from loco motors?

A. Not always. Also bear in mind that removing the capacitor(s) could render the manufacturer warranty invalid in some instances. Some decoders do operate more efficiently with capacitors removed and many modellers find that Bachmann models in particular run better without the capacitors installed. However, this does not always seem to be necessary. The answer seems to be try running the loco and if it is difficult to control at slow speeds or suddenly takes off like a jack-rabbit then remove the capacitor - if there is not a need, leave the capacitor alone.

Decoders

Q. What does "DCC Ready" mean when applied to a loco?

A. This is an interesting question. The term is misunderstood by many including, apparently, manufacturers. Essentially all the term means is that a 6, 8 or 21-pin NMRA socket has been installed into the loco. This should enable a decoder to be installed by just plugging it in to the socket. Whether the decoder will actually fit into the loco is another question! UK steam locos seem to be the worst offenders where manufacturers install a socket but leave little room for the decoder. Also check under the socket to ensure that none of the solder pinnacles come into contact with the metal body and also that there has not been any solder "bleed" between one pin and another. Both of these are faults we have discovered whilst installing decoders into DCC Ready locos.

Decoders

Q. How do I set the CV values to achieve slow running?

A. Best slow running is always achieved by setting your throttle to use 128 speed steps. Many decoders currently manufactured contain BEMF, which essentially provides automatic control of the speed of the loco to maintain a consistent speed. Some decoders allow you to set a cutoff point for the activation of BEMF (such as TCS) so that it is only active at slow speeds. You also need to remember that every loco motor/decoder combination is slightly different so settings might vary accordingly. In general, though, you should start by adjusting CVs 5 and 6. CV5 sets the top speed of the loco so if you want slow running set this at a value of 90. CV6 is the mid-point between 0 and the value of CV5. This would produce a speed curve which in reality would be a straight line. However, if you want slow running you need to set CV6 at a HIGHER value than the midpoint so that the curve is very gradual up to the mid point setting, then accelerates more rapidly after passing that point. So, if CV5 is 90 set CV6 to 60 - use these as starting points and adjust as necessary.

If you have a computer interface and your system allows the use of generic software such as JMRI (the Prodigy systems only allow you to use their own software) then you can see the speed curve in graphical form and adjust the level of each speed step on the graph.

Experience has shown that in general terms steam locos require more careful adjustment of CV values than diesel locos in order to achieve slow running.

Decoders

Q. How do I stop my Loksound decoder (also used in Bachmann and Hornby sound locos) from resetting itself?

A. It is possible to set the decoder so that it "remembers" (at power up or when the loco is selected and the sound activated) that it does not have to go through the whole sound start-up process every time.

Set CV124 to a value of 6.

Decoders

Q. How do I control the volume of my Loksound decoder (also used in Bachmann and Hornby sound locos)?

A. Sound volume on Loksound decoders is controlled via CV63. The maximum value is 64 but this will probably be too high for most uses. Try a setting of 20 first of all and adjust up or down to suit your own requirements.

Decoders

Q. How do I set the maximum speed of my loco which has a Loksound decoder (also used in Bachmann and Hornby sound locos)?

A. Maximum speed is set using CV5. On most decoders the range of settings for CV5 is between 0 and 255. However, Loksound decoders use a smaller range, so that you can only use values between 0 and 64.

Decoders

Q. How do I reset my Loksound decoder to factory defaults?

A. The straightforward answer is - DON'T!! Unless you know exactly what you are doing, that is, and/or have a copy of the sound project and the tools to reload it on to the decoder. If you reset a Loksound decoder you run the risk of losing the sounds that are programmed into the decoder as sound projects from different sources use different CVs.

Decoders

Q. What are CVs?

A. CV stands for Configuration Variable. Setting these variables (CVs) enables decoders to control various features of the loco or accessory. By changing these variables you alter the characteristics of the device you are controlling. For example, you can control individual lights, sounds, speed or even the direction the loco travels in.

CVs

Q. Why is CV29 so important?

A. CV number 29 is one of the CVs that all decoder manufacturers have to follow the same (NMRA) rules for how it can be used. This CV tells the command station whether the decoder has been configured for 4-digit addressing, whether it is set up for use on a DC (analogue) system, how you have set the decoder to control the direction of the loco, the number of speed steps you want to use and whether you are going to use a separate speed table. You can find out more detail about CV29 and a lot of other CVs by clicking here.

CVs

Q. What is a BUS?

A. No, it's not a vehicle for transporting people! Well, not in the world of DCC. It is a cable for transmitting data. In DCC there are normally 2 buses that are referred to - the POWER BUS (cable connecting different parts of the layout with electrical power and along which data is sent to decoders) and the COMMAND BUS (a cable connecting CABS together with the COMMAND STATION).

Wiring

Q. What are power districts and do I need them?

A power district is a section of track that is powered separately from other sections of track on a layout. How many power districts you have usually depends on the size of the layout. For larger layouts some power districts may have additional power boosters if they are a long way from the main power supply. Even on a small layout, though, you might want (or need) more than one power district. Separating a layout into power districts means that if one section becomes inoperable for some reason (like a short circuit, for instance) the rest of the layout will keep functioning. It is possible to have a number of power districts using only one power supply. There are a number of circuit breakers available on the market from a range of different manufacturers so choose the one thatmost closely fits your own requirements.

Wiring

Q. What is feedback and why would I need it?

A. Feedback is required if you intend controlling your layout by any form of automatic control. A fundamental element of any DCC system using automatic control is the block. So you will need to divide your layout into blocks, each block having a block detector. The detector reports back to the control system whether or not the block is occupied - this is called feedback. There are other elements of feedback, such as the position of points and status of signals, so that the computer has a complete picture of the layout status at any one time.

On the NCE system feedback is fed back to the command station (and thence to the computer system) through a device called the AIU (Auxiliary Input Unit). Each AIU has 14 inputs and the device plugs into the Cab Bus. Unfortunately the PowerCab system isn't sufficiently sophisticated to run this type of system, which is why you would need the PowerPro. If you have initially purchased a PowerCab starter system but want to move to computer control you can do this by just purchasing the PH Box (sometimes called the System Box) - this will give you a full PowerPro 5 amp system without the need to purchase any additional throttles.

Wiring

Q. What do I need to consider when wiring a DCC layout?

A. There are a number of things to think about. Click here for some useful guidance.

Wiring

Q. How do I solder track and bus wires when wiring a DCC layout?

A. There are a number of YouTube videos which give some guidance and techniques that can be used:

Video 1 Video2 Video 3 Video 4

Wiring

Q. What are DCC friendly points?

A. Any points can be used on a DCC system, so the simple answer is any! Some point manufacturers, such as Peco, provide information to modify the wiring under electrofrog points to ensure that current flows in the right direction when switched.

If you wish to use Peco point motors for control by your DCC command system then use the PL10W as they have a lower current requirement.

It really depends if you are going to control point motors through accessory decoders as some makes of point motor (such as Fulgurex) are more difficult to control in this way.

Track and Points

Q. Do I have to modify points for use on a DCC system?

A. The simple answer is no. Both insulfrog and electrofrog points can be used without modification. HOWEVER, it is VITAL with electrofrog points that rails leading to the inner part of the V MUST be insulated or otherwise you will get a short circuit - that is guaranteed and will not do your loco decoders any good at all!! In the ideal world, though, there are some modifications you could/should make, and there are several sources of information on how this can be done - one example here. For a video of how to wire up an electrofrog point click here. There are also devices now available, such as the Hex Frog Juicer, that can help eliminate short circuits on points.

Track and Points

Q. How do I install a solenoid point motor and wire it up to a mimic panel?

A. See here for a pictorial illustration of one method that can be used.

Track and Points

Q. How do I solve the problem of a reverse loop on DCC?

A. Unlike a DC system, where the operation of a reverse loop is usually operated manually via a switch, a DCC system can automatically detect when a train is in a reverse loop and switch the power between the tracks once everything is clear to avoid a short circuit. There are a number of reversing modules available from a variety of manufacturers but you need to make sure that the reverse loop module you purchase is compatible with your DCC system as a number of those available have a power requirement that might be too great for your system. For example, the DCC Specialties OG-AR Auto Reverser and Circuit breaker has a power requirement of 4 amps so will not work with many DCC starter systems that have a lower power output.

Track and Points

Q. How do I keep track clean?

A. There are various ways of keeping track clean on a DCC system. One thing you CANNOT use is a Relco track cleaner - this will destroy your DCC controller! The best way of cleaning track, and especially if you have any tunnels or track which is difficult to access, is a CMX track cleaning wagon - to see how this works, see this video.

Track and Points

Q. As DCC has a continuous power supply, how does this affect lighting in coaches, for example?

A. As the whole layout is powered continuously this means that coaches can also be lit, even when they are not moving. One way of doing this is shown in the video here.

Lighting

Q. Can I control lamps on steam locos?

A. With continuous power to the track lamps installed on locos can be lit as required, so it is possible to have both head and tail lamps. One issue is that one installed lamps cannot be removed so you will need to consider what lamps are necessary on any particular type of loco. If you have a number of lamps on the front end of a loco it is possible to control individual lamps with the use of functions - the more functions a decoder has the more control you will be able to exercise. However, bear in mind that if you want to add smoke this will use one function (or possibly two, depending on the smoke unit used and the output current of each decoder function) One way of combining both loco lights and smoke this is shown in the video here.

Lighting

Q. What do I need to install lamps on steam locos?

A. You will obviously need some loco lamps!! These are more widely available now ready made and with NANO LEDs already installed. Those from DCC Concepts are extremely good and available in standard BR or LNER designs, with both red and white versions available. You will also need resistors to prevent the LEDs from being over-powered and, depending on the space available inside the loco, a small circuit board on which everything can be assembled. This adds to the complexity of the wiring and soldering required, though there are now decoders coming on to the market, such as the KAM-LED versions from TCS, which have resistors built into their circuitry, thus eliminating the need for separate resistors to be added.

Lighting

Q. How can I add LEDs into my DCC stock?

A. See this useful beginners guide to the use of LEDs in DCC fitted products - click here.

Lighting

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