How to Install DCC
on Your Model Railroad

DCC (Digital Command Control) has revolutionized how we run model railroads.

>However, I think it is more fear of the unknown than the cost that is making many model railroaders shy away from making the switch from DC to DCC.

Many manufacturers are responding by installing decoders that operate on both analog and digital layouts. The same applies to sound.

To me this is like putting only one foot in the water. You never learn to swim.

Yes, there's a learning curve but it is not as daunting as you'd think.  Here are a few things I've learned:

  • Use AWG 10 wire size in black and red for your main power bus. Better to be too heavy than too light. 
  • Keep the wire parallel to your mainline track underneath the layout. (See my page "To Twist or Not to Twist")
  • Colour code the wires when you add feeders so you always have a visual reminder of whether you're connecting to the front rail or the back rail.  I use black for the negative (-) rail. Just be consistent.
  • Use smaller wire for short feeders to the bus (18-22 awg.

I had a lot of telephone cable I got from somewhere years ago. It's not much fun to unravel all the wires but it was cheap.  Unfortunately, it means I'm breaking a cardinal rule of keeping colors consistent.  As the telephone wire is wound in pairs I find it easier to keep track of which feeder is going to which rail because the colors are opposite, eg. red/green and green/red. I promised myself to be more consistent on the new UNRR.  

  • Solder directly to the outside edge of the rail.

Some modelers like to solder to the bottom of the rail or to a rail joiner before installing the rail. I find this more time consuming.  After I paint the side of the rail the solder isn't very noticeable.

wirecuttersProper wire cutters

Use a wire cutter tool to spread the insulation on the main bus wire so that you can wrap the other end of the feeder around it and then solder. The 10 gauge wire soaks up a lot of heat so you need to use a heavier soldering iron. 

   Some modelers use suitcase connectors but I don't have experience with them. Also the soldering method is cheaper. Every model railroader should learn how to solder correctly.

  • Try to feed to each rail between rail joiners, especially where track will be hidden or difficult to reach. Sooner or later a rail joiner will fail to conduct electricity. Usually the farthest one away or the ones under the mountains in a tunnel!

To block or not to block,
that is the question.

I converted a lot of my previous model railroad from DC to DCC which meant the blocking was already in place. I'm glad it was. While you no longer need it to keep engines separated, the blocks help to isolate sections to make it easier to find short circuits.

I put a DPDT (double pole double throw) toggle in the layout's fascia near the isolated section and used one side of it to cut power to both rails. If I get a short I can shut down all or part of the railroad and then turn it back on section by section until I find the area that has the short circuit. 

The other side could be wired for lights. I just happened to have a lot of DPDT toggles left over from the old DC panels I first built. Fortunately, most model railroaders are pack rats and never throw anything away. You never know when something might come in handy!

By the way, start with the simplest solution. ls an engine sitting across a gap in front of a turnout frog?  We all tend to over-complicate and assume the worst. I remember one time when it took me about three hours to find a problem. I had attached some weights to the bottom of a hopper car. The car was in the back of my hidden staging yard. The weight had fallen off and was shorting across the rails. Proved my point about electrically blocking the layout. I'd still be looking for it.

power shields circuit protectorsPower Shields

Later I added a booster to divide the layout into two major sections and installed PowerShield circuit breakers from Tony's Train Exchange. Now the entire railroad didn't shut down when there was a short in one section and everything was better protected. Adding circuit protection is a very worthwhile investment and they are day to install.

model railroad control panelControl panel

My main control centre was nothing fancy. I bought a small cabinet at Home Depot and added castors to the bottom. The cabinet had a roll-out shelf.

I put the Lenz controllers on the shelf and secured all the wires behind them with terminal strips.

I'm doing the same thing on the new UNRR. Other power supplies, such as a 24 volt DC supply for relays and a capacitor discharge controller for twin-coil switch machines, are kept on the lower shelves along with some manuals. I can keep the cabinet under the benchwork and be able to pull it out when I need to add wiring. I can also pull out the shelf.

On the previous layout the control panel with the track diagram was used to control the electrically operated turnouts in Utopia. The diagram helped operators see where the tracks went.

Blocking is also important if you plan to install signalling that requires track detection. At first I took a shortcut by using LogicRail's signal boards that rely on optical sensors buried between the rails. It's not quite prototypical to do so because the signals will revert to green after 30 seconds but they're still fun to watch. Afterwards I installed signals that use current transducers (CT) to detect current flow in a block. This involved isolating one rail with gaps.

For more information go to my signals page.

How DCC works

Martin Alborough, who set up and runs the NMRC website has written a very good layman's explanation of how DCC works. Go to the club's website to see it.

Which DCC system is best?

That's a matter of personal preference. I Use Lenz because that's the system I was first introduced to. I've operated on a Digitrax layout and like that as well. Our club uses Digitrax. Free-mo has chosen Digitrax as the module standard so take that into consideration if you plan to go modular. 

I've also used North Coast Engineering at an operating night during a Northeastern Region (NER) NMRA meet. That has some great features too, especially for large layouts with lots of operators.

I recommend choosing a system that is well-supported by your local hobby shop or one used by friends or a local club.

If you are a loner or living in a remote area, you can always get excellent support from Tony's Train Exchange or other members of the DCC Manufacturer's group.  Check their ads in the model railroad press for a list of DCC retailers near you.

I also recommend buying a book such as Digital Command Control, the comprehensive guide to DCC  by S. Ames, R. Friberg and E. Loizeau published by Allt om Hobby in association with the National Model Railroad Association.

Kalmbach Publishing Company, publisher of Model Railroader magazine, has three clearly-written guides you might like to consider. You can find them at better-equipped hobby stores or order direct from Amazon. Here are the ones I recommend.

If you use or plan to buy Digitrax (which our club uses), then here's the definitive book.

Then buy an engine with a factory-installed decoder, with sound if you can afford it. Or take one of your older engines like an Athearn or Atlas diesel and install a decoder to gain confidence. 

If you'd like to see how I overcame my fear of installing decoders in my old fleet, check out my installations in an Athearn switcher and sound installations in some older Atlas RS3s. 

<p>See how I installed a decoder in an older  Athearn switcher.

This is how I installed a sound decoder in an older Atlas RS3.


Plug 'n Play Decoders

These are some tips I picked up at a DCC clinic at the 2008 NMRA NFR convention in Ottawa, Canada. Loy Spurlock, a DCC guru and now retired from his company, Loy's Toys, conducted the clinic.

An NMRA medium connector has two rows of 4 pins for a total of 8. Pin #1 usually has some sort of mark to identify it.

Pins are:

  • 1 motor + orange wire
  • 2 rear light yellow wire
  • 3 Normally not connected.  Lifelike uses it for a mars light. Brown may be used instead of green by some manufacturers.
  • 4 left rail pickup black wire
  • 5 motor - gray wire<
  • 6 front light white wire
  • 7 common blue wire
  • 8 right rail pickup red wire ("Red Right Rail")

Use an ohm meter to check that the motor is isolated from the frame and rail picks ups when you remove the dummy plug. This is critical. If you install the decoder backwards, ie, pin 1 goes to 8 and 8 goes to 1, the engine will run the wrong way but you won't hurt anything. Unplug and reinstall the decoder correctly.  

Pin 7 is "raw power" common and is often 1.5 volts less than track power. It should not be thought of as "ground".

Sound installations usually use purple for the speaker connections such as Soundtraxx LC series decoders.

Stall current

You can check if a locomotive's stall current is compatible with the decoder you want to install. This can be more important with some sound decoders or if you have to use a small low current decoder due to a space problem, such as an N-scale decoder in an HO engine.

Place the engine on a section of track powered by a conventional DC power pack set to 12 volts for N-scale and 14 volts for HO and S scales.  Connect a DC ammeter in series with one of the track feeders. If your power pack has meters built-in you can use those instead. While holding the engine lightly on the track, turn on the the power pack. Stop the motor from turning by pressing the wheels down on the track or hold the flywheel or drive shaft. Make sure that the the power pack is turned to the full voltage as noted above (12 or 14 volts).

Measure the current the engines is drawing while the motor is stalled. This stall current must be less than the decoder's rated capacity.


Loy recommends changing the bulbs, especially in Lifelike locomotives because their bulbs are high current draw, often 100 milliamps (ma) or higher. Digitrax decoders can normally handle 1/2 amp but NCE and others usually only hnadle between 20-40 milliamps. 

A typical 12 volt bulb needs a 120 ohm resistor. Install resistors to the function lead, not the common.

Use 30-40 ma bulbs with 1/4 watt resistors. With LEDs, use a 1K resistor. You don't need to calculate the resistance.

Atlas consistently uses 12 volt bulbs. Use 100 ohm resistors.

Loy noted that Richmond Controls makes a very tiny LED that's very bright. It can take up to 3K resistance.

If an engine is going in the wrong direction, reverse the motor leads. This is often easier than doing a software fix.

Clips are designed for the thickness of the respective boards, such as Atlas. If soldering, don't stick the wire in the holes on the decoder. 

Just strip the wire 1/16" to 1/8",tin it, and solder quickly to the pad. If using the clips, use heat shrink tubing on the wire that passes through the hole in the pads.

  • For low voltage decoders, wire bulbs in series.

Note that on Likelike Proto 1000, 2000 engines, there are traces on the boards that must be cut. They are marked with an X. Use an ohm meter to check continuity.

A 120 ohm 2-watt resistor can be used to limit current for a programming track if your system doesn't include a programming track.

LED turnout indicators

Here's an idea for  route indication on power routing turnouts on DCC layouts.

DCC Hard Wiring Tips

Loy had some tips about hard wiring an Athearn locomotive that I found helpful in doing my own installations. He suggested to file clean one of the holes into which the motor is mounted. Install a wire into the hole and then push the motor back into the hole. This will fix the wire in place instead of soldering.

It is possible to solder to the side frame. Eliminate "slip joints" wherever possible by using conductive fluid, the stuff that is used when mounting heat sinks. I prefer to drill and tap a #00-80 hole and then solder the wire to a metal washer on the screw. You need to drill slowly and use oil on the drill bit.

Loy also cautions about using black electrical tape to insulate because it gets sticky when hot. He suggests yellow tape or even Scotch tape.

Setting CV29

CV29 controls a lot of things and it can spook modelers who are unfamiliar with binary math, like me! Because there are 8 bits in a byte, it is a simple matter to add the bit numbers together to reach the number you want.  If a bit is turned on, count it as a 1. If turned off, count it as a zero. Use the table beloe to help you.

128 64 32 16 8 4 2 1
7 6 5 4 3 2 1 0

To make a locomotive run forward, CV29 should be a 6. Look at the bottom row. 

Bit O is turned off so you count it as a zero. Bit 1 is turned on so it is counted as 2. 

Bit 2 is turned on so you count it as 4.  0+2+4=6. 

If you want the engine to run backwards and you don't want to rewire the motor, change the value in CV29 to 7 by turning on the first bit. 1+2+4=7.

You can use Decoder Pro to do a lot of this calculating. Loy also suggests that if a decoder doesn't work, check the value in CV19.  If there is a value, change it to 0. This often solves the problem.

DCC spike suppression

Loy recommends connecting a .1 microfarad capacitor and a 22 ohm 2 watt resistor between rails on the bus wire at the furthest point of track feeders or halfway through a loop.

Use of CV11

I learned something useful a few years ago on the Lenz forum in Yahoo Groups in which I'm a member. 

I have an HO Proto 1000 RS18 diesel with a QSI Quantum sound decoder.  The engine kept stalling every 5 or 6 seconds. It cut out for a second or two then started moving again exactly as if nothing had happened. I thought I probably had some anomaly in the decoder or on the X-bus.  It didn't happen when the locomotive was used on our club layout that uses Digitrax. Nothing I tried seemed to work. I reset the loco on Decoder Pro in Service Mode with a PowerPax booster installed on the programming track and even changed a few CVs for top speed, startup, etc. Nothing worked. Then, Mike, a member in the Lenz Yahoo group, suggested the problem might be in the memory stack. 

  • CV11 is involved with the timing of instructions being sent to the decoder. 

Evidently this member of a Lenz-equipped club had encountered this problem. What was happening was there was a lag while the decoder in the locomotive waited for the next instruction. Mike suggested I change CV11 from 0 to 20 to change the timing. This immediately solved the problem and the RS18 now runs like a charm. Mike says his club now sets all its decoders to 20 in CV11.

If you experience a hesitation in one of your locomotives and you have already eliminated dirty track, dirty wheels, bad pickup and everything else you can think of, try changing CV11 to 20.

I know that on Digitrax it is necessary to clear the memory stack when its gets full. I'm not sure about NCE or other systems. 

I've never paid any attention to it on Lenz because we just call up another loco on the LH100 throttles and that automatically replaces the one that is there. Doing so overrides other throttles that have the same engine number listed.

I usually had 20 or so locomotives running, doubleheading, or idling in a yard so I had to be chewing up a lot of memory and slowing down the packets of bits and bytes. 

Anyway, this is a fix worth knowing about, especially if you use Lenz.

Booster feeders

Put feeders near the gaps between sections. Make sure this is also done on reverse loop sections.

Here endeth my notes from Loy's clinic on DCC. Hope this information helps.

My best tip?  If I can do it, so can you.

Making your own DCC system

This is beyond my ability, but my friend John Houghton has put together a very inexpensive DCC system. I'll let him describe it in his own words:

"A while ago I bought a Raspberrypi3 small computer. Search for it to get the details but the skinny is, $50.00C gets a powerful Arm based computer the size to fit in a shirt pocket, similar to an Arduino. At the time I had trouble getting it working then realized I had bought a cheap, slow memory card for it. Once this was replaced, things worked really well.

The goal is to use the rpi3 without a monitor, keyboard or mouse to run JMRI and access it from my iPad to make things happen.

I [now] have it working. JMRI is installed on the rpi3, it auto starts web server and WiThrottle server so connection as usual to JMRI from my iPad. To get me access to the rpi3 desktop I had to install an app tightvncserver onto the rpi3 then configure it to automatically start on boot of the rpi3. Got this working. Then I downloaded the app VNCviewer to my iPad, registered and connected to the rpi3.

So my proceedure is:
Plug in the rpi3, there is no on off switch.
Wait til the rpi3 lights stabilize then start VNCviewer on my iPad.
VNCserver is auto running on the rpi3 so I simply tap to connect to the rpi3 from my iPad and I get to my rpi3 desktop where I then can start JMRL PanelPro and it starts web server and WiThrottle.
Switch to WiThrottle app on my iPad and I am in business as usual.
I am following this procedure as I want to shut down the rpi3 properly by software shutdown and not just unplug the rpi3. So, I simply switch back to VNCviewer app, close JMRI and shutdown the rpi3.

Next in line is to fully connect JMRI to DCC++. What is that you ask?
An Arduino based DCC command station that runs trains via standard DCC connection. Buying from China, I got an Arduino Mega for $12.00, or $65.00C for Sayal,a motor shield for $6.00, $35.00C at Sayal, free download of the DCC++ software and setup on JMRI to DCC++ in similar way as Digitraks, Lenz, NCE etc.

For $70.00 I have a fully operational, powerful DCC system.


Drop me a note via my Contact Page if you are intrigued by what John has done and I'll forward your questions to him.

Go from "DCC" to DCC turnout frog wiring.

Go from "DCC" to Decoder installation tips for an older steam loco.

Go from "DCC" to Decoder programming.

Go from "DCC" to Motor isolation in a brass diesel.

Go from "DCC" to HOn3 shay remotoring and decoder isolation.

Go from "DCC" to Adding phosphor bronze wire for all wheel pickup.

Go from "DCC" to Decoder installation in a brass engine.

Go from "DCC" to Servo control of turnouts with Tam Valley stationary decoders.

Return from "DCC" to my Home Page

Like to become a "solopreneur"
with your own online business?

New! Comments

Have your say about what you just read! Leave me a comment in the box below.
Copyright© 2008-2017