Clinic Handout 
Tips & Tools 


Selecting an NMRA DCC System for S scale
by Michael Greene

When it comes to power options for your model railroad, the way I think of it is that S has the most flexibility you will find in any model scale. You can easily choose to power your railroad with AC, DC or DCC. Once you make your choice, then you just make sure that the locos you acquire for your railroad are set up for that power option. I'll continue the discussion with the assumption that the choice we've made is to power it with DCC.

Often times one of the first question asked is how "big" of a DCC system do I need for my layout. To help answer this, it is helpful to recognize that DCC is a little different. Unlike standard DC or AC, you can have multiple locos running on the same track at the same time with independent control. So what you need for power is really based on how many (and which ones) locomotives you plan to operate SIMULTANEOUSLY. Don't worry if this changes over time, because DCC allows you to add additional power stations to your layout over time, to support more things operating simultaneously.

In order to get a rough idea of the power you need in your initial DCC system, add up the operating power requirements of the locos and other items you will power from the track simultaneously. (Notice I used simultaneously several times -- just because you might own 20 locos, it does not necessarily follow that you will run all 20 simultaneously, so you don't have to add every one of them to your power requirement). A good rule of thumb for S is to figure 1 amp per loco running simultaneously. Some require much less (SHS SW9/1200s & SW-1s are less than less than 0.5amp each) and American Flyer locos with their original motors are a bit more than 1 amp. But the rule of thumb is pretty good unless you know specifically what DCC components you will have. You also need to think about those other things you power off the track like lights in passenger cars, since they draw a little power as well, so you'll want a little extra cushion.

Regardless of how a manufacturer packages it, every DCC system is made up of five basic components:

  1. Decoder (usually located in the locomotive, although you can put them in other things as well): decoders are very small electronic devices that are installed in each locomotive you will run on your layout. These devices have a unique "address" much like your house has a unique address. In addition to setting the loco's address in the decoder, it also allows you to customize other operating characteristics. The decoder has connections to the track, the motor, and to any lights or other accessories in your locomotive.  Decoder come in a large variety of shapes, sizes, and features, from very simple decoders that control the motor and the forward light (headlight), all the way to higher end sound decoders (e.g., decoders from SoundTraxx and ESU) that control several functions and have sound functions like horn, bell, dynamic brake, etc.
  2. Cab (aka Throttle) - allows you to control your locomotive (things like change the speed, turn lights and/or sounds on and off)
  3. Command Station - converts the cab knob movements and button presses to special instructions that are sent to the decoder via the track
  4. Power Station - takes the low power signal from the command station and adds "beefy" power to it to actually provide power to the decoder & locomotive; typical power station sizes available on the market are 3, 5, 8, and 10amp.
  5. Simple Transformer -- usually an simple AC transformer (read cheap) with 110V/220V on one side and 15-18VAC on the other side; this provides power to the Power Station. From a size perspective it should be at least as big as the power station. A 5amp power station ought to have at least a 5A transformer, or said another way, if you only use a 3 amp transformer with a 5 amp power station the maximum you can get from the power station is 3 amps. This does not need to be a variable supply like a DC power pack, or a Lionel ZW transformer. And many HO/N hobby power packs  actually have very little power in them -- perhaps 1-2 amp.

Most of the DCC starter systems combine items 3 & 4 in to the same box/package. Some also add a Cab into the same package. Most systems allow you to have multiple cabs connected at the same time, since you usually need this to control multiple locomotives. For various reasons most DCC manufacturers do not include the transformer in the same package as the command station and power station.

The DCC system you start with really depends on a variety of things. Of course if you have a very limited budget, then this may constrain your options. But given that the budget is not the single most important factor in the decision making process, then in my opinion, for S scale and in particular if you want to use sound decoders like SoundTraxx, I'd suggest getting a DCC starter system with at least the following 6 characteristics:

  1. a Cab you like
  2. a Cab you like
  3. a Cab you like
  4. a Cab that can easily (for you) control 8 functions
  5. a power station with at least 5amp capability
  6. the ability to read values back on the programming track

Regarding item 4: of course you can start with a system that controls a smaller number of functions. However, please be aware that sound decoders like the S Helper Service DCC decoder (made by SoundTraxx) available on the F-3's and F-7's , use as many as 8 functions to control forward light, rear light, number boards, horn, bell, MARS light (if there is one), dimmable head light, dynamic brakes, etc. In fact the DCC standards provide for the option of 12 functions plus forward/reverse light, and as manufacturers build us products with "all the bells and whistles", many of these functions will be used.

The reason I recommend 5amp power stations is that using this size for S scale generally allows 3-6 operating locos, plus a little cushion for track powered car lights, caboose lights, etc. Also SoundTraxx decoders have a higher initial startup power draw than non-sound decoders due to some capacitors on the board that need to be charged.

And notice about the cab -- it's on the list three times because based on my experience it is the most important choice you will make. If you the modeler don't like the cab, and/or its not easy for you to use, then you will get frustrated. So if possible try them out before you buy -- each manufacturer's is different. And most manufacturers even offer a variety of cabs within their own product line. This means that as you add additional cabs you can choose whether you want every user on your layout to have all the functions the advanced cab offers, or you want them to have a subset, that might be simpler for them to operate. One other note about the cab - you generally cannot mix cabs from different manufacturers on your DCC system. The DCC Command Station you choose will determine which cabs will be available to you.

Base on these requirements, in my opinion some starter sets you might want to consider (in no particular order) are:

  • Lenz Set-100 (also Set-90 if you are not planning to operate sound decoders)
  • NCE Powerhouse Pro
  • Digitrax Super Chief (with DT400 cab)
  • CVP EasyDCC (with 8 function cab)
  • Wangrow System One

You can certainly get by with lower end (aka entry level) system if for example you only plan to run one or two locos. But you may find a while after you purchase it, that it does not meet your needs, or you find the more limited cabs that come with entry level systems make controlling all the functions on your loco more difficult (e.g. you might not be able to access certain functions, or you might have to press more than one button every time you want to control a certain function). Some of the entry level systems can easily grow as your needs grow, and other entry level systems may require that you replace your DCC system in order to meet your changing needs.

If you're looking for more details about various DCC components, and their application in S scale, you might want to review the Getting Started with NMRA DCC document found on the clinc handout page.


Copyright 2002-2007, C. M. Greene. All rights reserved.