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Overview and introduction to DCC

OK, while I think this falls into the FAQ category, I am going to put my "DCC introduction" here. I really suggest you read this. Yes, I know, you are excited, and want to know which system is "best" RIGHT NOW so you can run out and buy it and get started. That is the wrong way to go about this, please do yourself a favor and read.

I want to take a different "tack" than how the subject is often explained. No need to dive into the internal technology, show waveforms, describe binary numbers or even explain CV's right now. That's not what you need to know right now.

There are also books and presentations on DCC, but often this information is either biased to a particular manufacturer, or 10 to 15 years old. (The much-vaunted "Big Book of DCC" is completely slanted to Digitrax and was published in 1999). I recently tried to correct a post on another popular "DCC wiring" forum, and the author and owner of the group would not even bother to respond, my post got nowhere.

If you are new to DCC, my best advice is to FORGET everything you have heard about DCC, unless you have a friend that uses it successfully and can explain it to you, and is open to options other than his personal choice. (good luck!).

As with anything in the world, if you are asking questions of an "expert" and they cannot explain things to you in layman's terms, get yourself a different "expert". Try this simple technique, it will show up the charlatans and pompous know-it-alls.

If you are new to the hobby, or have been listening to someone who does not use DCC, you probably have a head full of bad information (especially battery power people). It is no longer 15 years ago when the whole thing was unreliable, user unfriendly, and difficult to understand. If you have been given that impression, that person is not familiar with today's DCC, or is a battery junkie. This is what you will hear from people who don't understand it, or are anti-DCC, there are plenty of people like this, unfortunately.

Stop listening to people who have a chip on their shoulder, know nothing about the subject or just want to show everyone they made the right decision no matter what.

Here is a link to a nice introduction to DCC presented by Eric Eggel to the O Scale West convention in 2015, download and read it. DCC Intro pdf ... just read the first few pages, it's from an O scale club, so take that into account.

To start: Let's talk about what DCC can do for you:

  • Uses track power - less expensive than batteries and chargers, easier to install, and you can have remote control and sound and smoke in tiny locos, and never worry if your batteries will run out too fast. (typical naysayers tell you that battery power is cheaper, BS: list up the costs yourself)
  • True independent operation of multiple locos on the same track.
  • Reduced wiring complexity, no need for separate power "blocks" in 99% of layouts
  • Products available from many different manufacturers, lots of options and since it is a standard, you can "mix and match" components.
  • Many different throttles to use, and different levels of functions and complexity, size, etc. Pick what you like.
  • Interfaces to computers with software that allows automated running. There are plenty of free software packages by the way.
  • Biggest lie from naysayers: There are many different features BUT you do NOT have to use or learn them all, EVER. (again, forget what you have heard).

Using DCC

When someone is evaluating using a new system, you normally talk "user-friendly", so I will try to look at it from a new person's perspective.

A new user wants to get up and running quickly, so the basic functions need to be simple, and more importantly, there need to be "default" settings to help this.

(I have to also set the stage with some basic assumptions, the locomotives have sound already also.)

So, these first steps would be (in my opinion) (and picking non-DCC terminology):

  1. connecting the system to the track (just 2 wires)
  2. connecting any components together (normally just plug the throttle into the "command station", not needed with wireless throttles)
  3. taking a new (out of the box) locomotive with a factory installed DCC decoder (receiver), identifying the locomotive's "name", i.e. "what I have to do it reference this loco".
  4. telling the system I want to control this locomotive (normally a 2 or 4 digit number)
  5. setting the direction of the locomotive (usually a direction button on the throttle)
  6. increasing or decreasing the speed of the locomotive. (usually a knob or roller or buttons)
  7. Blowing the whistle/horn (almost always a clearly labelled dedicated button)
  8. Ringing the bell (again a clearly marked, dedicated button)

These functions should be VERY simple. In my opinion, if you cannot show someone how to do this in under 5 minutes, then it is NOT user-friendly.

After this, then you would desire to go to the next level:

  1. customizing the locomotive name/identifier
  2. having a "quick list" of 2-3 locomotives "saved" in the throttle
  3. being able to switch between locomotives easily
  4. customizing the momentum of the locomotive for more realistic operation
  5. having a simple way to control more sounds
  6. easily running locomotives in multiple units or doubleheaded, or really anywhere in a train. (American bias)

Believe it or not, all of this is easy given a "good" system. These are the things I look for in a system myself, and when recommending to newcomers.
Funny, but some of the most popular and expensive systems fail these criteria.

OK Greg, I was patient, but what's the answer? What's the "best" system?

The cheaper systems have limitations (which you may not fathom yet) that really do not save you money. The better systems are really where you should go. Buying something and finding out in a year it's not doing the job is painful. Like your track, if you buy the right system, you can stay with it forever.

After a lot of research and reading lots of forums, I first settled on the NCE system for a number of reasons, I really like the Pro throttle, and the computer interface. The throttle has very good menus and operation, and the computer interface allows me to use the JMRI software (free) or even run trains from my iPad, iPhone or the (far superior) Android phones (ha ha, I don't drink the Apple Kool Aid!) .

NCE's wireless throttles work exactly like the wired ones, and have full duplex communications to verify the commands have been received by the system. (this turns out to be important).

Since my initial decision, I have experienced excellent service by NCE, the ability to contact an engineer at NCE for problems, and the great Yahoo forum for NCE. I'm still very happy years later.

After about 9 years, I changed to Zimo, because I needed some unique features they offered. It is a more complex system, and I often miss my NCE system, but I made the choice for some very specific and unique features that Zimo has.

How DCC works in general:

DCC uses a customized AC wave on the rails. The wave differs from the AC in your house in that the DCC wave is square, not sinusoidal, and the frequency of the AC varies to provide the commands. This is very like how a FM radio signal varies frequency.

A DCC system by NMRA definition uses 4 logical components (sometimes two or more of these are in the same "box"):

  1. A command station, the central component, which creates the DCC commands to the locomotive. It takes direction from throttles/cabs, and generates a low voltage DCC signal.
  2. A booster, which takes the low voltage DCC COMMANDS from the command station and BOOSTS it to higher voltage and amperage and puts it to the rails.
  3. Throttle(s), which connect to the command station (wired and/or wireless) which have the controls for speed, direction, and function buttons for sound, lights, etc.
  4. Decoder(s), in locomotive, rolling stock, and stationary ones that can control turouts, that "pick up" power and commands from the rails and controls the loco, lights, sounds, and optional extras. (not all decoders have sound in them)

Important note: The DCC power is a square wave AC signal. The timing/frequency of the signal is the "data" and the signal can be converted to power with a simple full wave bridge rectifier. This design makes it much more resistant to low voltage, bad connections, etc, since the power and data are combined. It's easy to "harvest" DC power for constant lighting, etc.

DCC decoders for G scale

G scale has some special requirements over smaller scales.

  • Higher current necessary for larger motors (several amps)
  • Higher voltage than the other scales (24 volts)
  • Higher audio power output for sound decoders (2 to 5 watts)

Note: initially there were only decoders that controlled the motor and lights in one package. Later there were decoders for sound only. Now you can get a single decoder that has both motor control and sound in it. (Saves money, space and wiring effort). Very few manufacturers make these separately now.

One relatively recent capability is using the motor BEMF (Back ElectroMotive Force) such that the locomotive's sound varies according to load, not just speed. (BEMF is a voltage produced by the electric motor that is proportional to load on the motor). The best decoders do this. Older or less expensive decoders only use voltage or the "speed step" to do this.

There are 2 ways to have sound and motor control that truly follows engine load:

  • an all-in-one decoder that combines sound and motor functions on a single board
  • 2 decoders: a motor decoder that "communicates" the BEMF levels to a sound decoder. The only practical way to do this is done is through the SUSI (Serial User Standard Interface). This method was the only way initially, but now is almost gone in current production, since it costs more, takes more hardware and space.

Why higher current & voltage and how much:

It's pretty obvious that physically larger and heavier locomotives and trains will require more power to run. Power is a combination of voltage and current. Under heavy loads, some locos can draw many amps. 

There is a large variance, but you should assume that your loco can draw at least 3 amps continuously under load. 

Measuring DCC voltage and current

The problem you will have if you are new to the hobby, you will have a hard time knowing what current your locos draw. Also, you cannot measure DCC voltage directly, since while it is AC, it is a square wave, and only expensive meters can read this accurately.

Thus, I strongly recommend getting a DCC volt/amp meter, and actually MEASURE voltage and current under load for yourself. There are so many variables, it's really a wide range.

Below is the RRAMPMETER by DCC specialties

Alternatively, you can get a "True RMS AC multimeter", but beware, the cheapo ones lie and they don't work. Stick with Fluke or Hewlett Packard.

dcc volts hp meter


If you are in the UK, you can buy an "Alpha" meter by DCC concepts



 Decoder requirements and information

Unfortunately, some decoder manufacturers rate their units optimistically, so you have to take that into consideration. In most cases I recommend a 5 amp decoder. There are some decoders that are rated lower that have no problems, like the original QSI, which can be run at 3 amps solid all day. Likewise, the Digitrax decoders have the reputation of blowing up on loads way under their rating. SoundTraxx also rates their decoders optimistically.

Current, running and stall

You also need to realize that the rating of a decoder is normally the "running" current, not the "stall current".

Note that EVERY time a loco does a standing start, it draws it's full stall current until the motor have a chance to spool up. This usually occurs at a short duty cycle unless you slam up the throttle, but the peak currents are still there if only for a short time. The Shay's peak current when running on track power is somewhat impacted by it's power pickup and wiring resistance. At the pickups, the stall current for the Shay at 18 volts or so is more than 7 amps. I could actually never physically stall the thing because it had so much torque. However, this implies that the actual motor stall resistance (which I never directly measured) is no greater than 7 ohms per motor. This is typical for Bachmann and Aristo motors.

I've toasted HO decoders in ONE motor large scale locos (those with the larger can motors). You can, if you wish, run trials by fire but it's your dime. Fortunately most decoder manufacturers have "no fault" warranties now and if you burn one up, you MIGHT be able to get it replaced if the manufacturer doesn't figure out what you did.

My preference is to use a beefy decoder and not mess with all this. I did find that the Aristo PCC could easily be driven from an HO decoder but that is because it uses small, high stall resistance, motors and high reduction gearing. An average motor current at 18 volts is about 200 to 250 mA, THIS is in the range of an HO decoder.

Voltage and current can be a real problem for people that run prototypical speeds on more modern freight and passenger trains.  It turns out that top speed is usually controlled by the "last few volts" on the track. Also, there is a non linear relationship of speed vs voltage.

Important note: There are some DCC decoders out there that do not handle G scale voltages well at all, even they are advertised as such. Decoders that meet the NMRA specs will have no problems.

The "Quasinami" (Soundtraxx oem) in the Bachmann 3 truck shay will freak out at somewhere around 20-21 volts. This is typical of many Soundtraxx decoders.

There are several decoders from Germany, such as the Dietz DLE 2M, that will not handle voltages over 18 volts. (It's actually more complex, where the 3 amp decoder cannot handle 2 amps and 18 volts at the same time, less amperage you might be able to run a higher voltage). This particular decoder is not really made by Dietz, but by Uhlenbrook.

The situation has probably come about by the manufacturers just putting larger transistors on the HO decoders, and not considering the necessity of higher voltage requirements.

Sound power output:

You need at least one watt audio power, and some sound decoders have more, but remember that in the world of sound, 2 watts is NOT twice the volume as 1 watt. This is true because your perception of volume is not linear, but exponential. This means do not agonize between 1 watt and 2 watts, you might notice the difference between 1 watt and 5 watts. Getting a "large scale" decoder normally guarantees sufficient power output. 

Combination decoders:

QSI Solutions Titan, by QSI Solutions, oem'ed from QSI Industries. New decoders that have motor control and sound. They are inexpensive (~$200), sound great, and make a plug and play decoder for Aristo locomotives (plugs into Aristo socket, no wiring). One of the best sound libraries, and new sound files are always being added. Unfortunately only found on the used market now.

Zimo, very high quality decoders. Huge selection of customization commands, but poor US "sound library", and many of the good sound files cost $25-$35 extra. Their programmer is more expensive, and documentation is translated German. Best low speed motor control.

ESU - Loksound - from Germany, documentation sketchy and just a few US dealers. They have downloadable sound files, but again, poor US sound libraries.  A bit tricky to set up. Good quality.

SoundTraxx - I waited 6 years for the large scale Tsunami, by SoundTraxx -  They never made it, but OEM'd some It looks as though they will never make these, too bad, they get great reviews on their HO ones. They made one OEM version for the Bachmann 3 truck shay, but no documentation, and it will often shut off on track voltages near 21 volts, which is necessary for large scale. The newer large scale ones are poorly scaled up HO decoders, and overload and overvoltage easily.

Massoth - very popular in Europe, they also make/made a lot of the LGB DCC stuff. An overly complex system that is a programming nightmare when you want to customize. If you buy this stuff, do not deviate from their setup, you will be sorry.

Motor only decoders

Lenz makes wonderful decoders, but nothing with high enough current capability for all G scale in my opinion. They work well with D.I.E.T.Z. sound decoders. SUSI is a serial interface that communicates the engine load and status to the sound decoder.

The total cost of the 2 decoders is high, and there is little support and few American sounds on the sound decoders. Maybe this will grow in the future, but cost wise, it's probably never going to be competitive with the single combination decoders.

Basically forget buying one of these unless you are already stuck with using an older sound only decoder.

Sound only decoders 

Phoenix - Great sounds and wide range of locos. The 2k2 was very popular, recently replaced by the P9B decoder. It is expensive (~$220). Works on DC too, so it has been very popular. Really limited in DCC operation, and expensive when you realize you need a motor decoder too, and the sound is not "coordinated" between the 2 decoders. Their first combination decoder is underpowered in current capability, and adolescent in its feature list.

D.I.E.T.Z. - popular in Europe, has typical problems of limited support, poor documentation, limited number of US loco sounds.

Ullenbrock - The Uhlenbrock is the Deitz rebadged, as is the programmer.

 I've left some of the other manufacturers out, they just make limited or difficult to use products in my opinion. As you become more knowledgeable you might try other products.

DCC power supplies

Again, you need big power. I have a 10 amp system that puts out 24 volts RMS (you need a special meter to measure the RMS voltage of a DCC supply) I think I might have to go to 15 amps, since I intend to have MU diesels of 5 or 6 USA trains F units. The "worst" loco that would be MU'd is probably the USA trains GP9, which has been measured at 9 amps or so at full stall. The moral here, 5 amps is not enough, and 8 might be marginal.

Many DCC power supplies are just a big AC transformer. You should have a circuit breaker and probably a fuse also. No real magic here, but I find unregulated supplies have noticeable "sag" under load. If you want to run higher speeds, like passenger or modern freight, a regulated supply is best.

Regulated supplies are DC, and not all boosters (see below) will accept DC input. I am very happy with my NCE 10 amp system which does accept either AC or DC. 

I am using a regulated power supply and it's much better and helps get proper top speed.

DCC booster

This "boosts" the DCC signal to the current and voltage to the rails. It has 2 inputs and one output. You feed the DCC signal and the raw AC/DC power and it puts the DCC signal "on" the power and feeds it to the tracks. Finding high amperage boosters is hard. The easiest to find is the NCE 10 amp unit. I've found 15 and 25 amp units in Germany, but never seen or imported here from what I have seen.

Some boosters have an auto reverse mechanism built in. You need this when you have reversing loops. Basically it senses a short circuit when a loco spans 2 sections of track with opposite polarities (or phase if you wish). It then reverses the track feed.

You can also get auto reversing units to feed separate blocks. The DCC specialites PSX-AR is the first autoreverser that works well for large scale.

DCC controllers

Here's where there are strong opinions and preferences.

Some people want a simple wired cab control. Advantages are ease of use for newcomers, children, and those who don't want a complex device. Disadvantages are the wire can restrict your roaming around, connector problems, hard to control advanced functions. If it takes you a lot of button pressing to control a function, then it becomes a lot less fun.

Wireless simple cab control. Pretty much the same as a wired one, but wireless controls are more problematic because of the wireless range and response. There aren't too many simple ones. Many of the wireless units have slow response to commands, and are not as reliable, i.e. you blow the whistle, but it doesn't. This is because most wireless units use one-way communication. The controller never knows if the receiver really got the command. This can be disasterous when you really need to stop!
The big advantage is you have no tether, the disadvantages are battery life problems, reliability, slow response, limited range, sensitivity to interference.

Wireless advanced cab control. Well, if you are going wireless, why not make it easier. The NCE controller is a good choice.

Computer control - another option is to interface to the controller by computer. This can allow unattended operation, advanced block control, and/or train location detection.

Some computer control options also include the ability to have the computer act as a server to other computers running programs to control locomotives. KAM Industries is one example. They also have a product that lets you use a hand-held PDA as a wireless controller. One advantage of this is that the wireless communication used is a standard protocol already in widespread use, 802.ll, a.k.a. WiFi.


DCC Variants

I'll expand this section. Most of the "DCC over the air" systems are not strictly DCC by definition, and ones that don't have a command station have less functionality than a real system. I will explain this.




Books to read: (from an MLS forum thread)

Digital Command Control - the comprehensive guide to DCC (Paperback)
by Stan Ames (Author), Rutger Friberg (Author), Loizeaux. Edward (Author)
Publisher: Tried and True Trains (July 1998)
ISBN-10: 9185496499
ISBN-13: 978-9185496495

The DCC Guide (Paperback)
by Don Fiehmann (Author)
Publisher: Kalmbach Publishing Company (October 2007)
Language: English
ISBN-10: 0890246769
ISBN-13: 978-0890246764

DCC Made Easy ( Paperback )
by Lionel Strang ( Author )
Publisher: Kalmbach Publishing Company

DCC Projects & Applications ( Paperback )
by Mike Polsgrove ( author )
Publisher: Kalmbach Publishing Company 

Links to learn DCC:


Matthias Manhart - Various DCC Decoder Installations

Arnold's Train Web - Interesting DCC projects for largescale trains




DCC calculator:




Click the links below to go "deeper" into details on individual DCC systems and other topics

  DCC Equipment by Manufacturer  
  DCC Wiring Tips  My Implementation   DCC sound decoders 
  DCC Programming Tips   Advanced DCC Topics    DCC Installations Overview   DCC in Z Scale 
  DCC S/W for PCs & Phones   How to choose your DCC system    DeadRail (DCC over the air)   
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