KB366: Some Thoughts on Decoder Installations

This article was last updated on Jan. 20, 2012, 12:23 p.m. | Print Article | Leave Feedback

There was a time when every mobile decoder installation was a custom installation.

In those early days, we were just feeling our way along, trying to find ways to make the existing supply of decoders fit into locomotives which had been designed in a different era.

Fortunately, things have changed along the way, and in many cases, the Digitrax
Decoder Selection Guide will list your locomotive.

But many locomotives are not listed because they are too new or are too generic for a special listing.

So, from time to time, you will have to "wing it" just a bit to get a mobile decoder into that special locomotive.

Likewise, you may be intimidated by the decoder installation process; you may have too many locomotives to convert, or you may not be able to do the installation yourself.

Let us give you some thoughts on the matter.


First, we hear some potential Digitrax customers saying: "I've got two hundred locomotives, how can I do that many conversions?"

We ourselves have that many, if not more, but the reality is that you usually only operate a few at any given time, so start by converting your favorite locomotives first and then slowly expand out into your fleet.

Decoder Installation
We also hear from some customers who are concerned that they cannot do a locomotive conversion.

This is understandable, but there are ways around this issue.

Factory Equipped
Now, there are many locomotives with Factory-equipped decoders, making conversion unnecessary.

Ahhhh, Modern Times!

Plug N Play
Likewise, there also are many locomotives that are Plug N Play; that is, these locomotives have a jumper plug on the circuit board inside the locomotive.

This plug is removed and a PS series Digitrax decoder is plugged into the open socket.

The only thing left to do is to change the decoder address from the Factory default of "03" to another address.

Professional Installation
Your dealer may be able to help you with the decoder installation and some locomotives require modification for a proper installation.

The Kato H0-Scale NW2 comes to mind; a very fine locomotive, it has no open space for a decoder and requires that the cast metal frame be modified to open up a space.

Although this opening process can be done with basic modeling tools, having a milling machine makes for a cleaner installation.

Most people don't have a milling machine, so there are also.....

Conversion Frames
Likewise, there often are conversion frames available for specific locomotives; these frames are designed with a location for a decoder.

You remove the old frame, transfer the motor and gear train to the new frame, install the decoder, close the locomotive back up and program the decoder address.

Of course, we make this sound very easy, and after you gain experience in the process, it will be easy for you also.

Decoder Selection
It is important to install the correct decoder into your locomotive.

There are several considerations:

Physical Size
The decoder must be able to fit inside the locomotive.

In many cases, the
Decoder Selection Guide will give you a specific example.

There also are many decoders that are designed specifically for certain locomotives; this is especially true for N-Scale locomotives.

Digitrax offers over a dozen board replacement decoders which are designed to make N-Scale conversions easier.

Other manufacturers also offer board replacement decoders for other locomotives, and since DCC is open architecture, Digitrax can control these decoders also.

The Digitrax decoders are grouped by general physical size; these are DZ, DN, DH and DG types.

It is important to note that although the DZ decoder is designed for use in Z-Scale, it is also possible to use it in other scales if the decoder's amperage rating is not exceeded.

The DZ series are perfect for very small locomotives in other scales.

Likewise, the DN decoders are sometimes used in H0 locomotives.

The DG series are used for larger scale locomotives; they are physically larger because their amperage capacity is larger to meet the power needs of the larger scales.

Amperage Rating
The decoder must be able to handle the electrical current which will flow through it to the motor and to the locomotive's functions.

In this case, stall current becomes important; stall current is the maximum amount of electrical current which the locomotive mechanism will draw.

Your choice of decoder will be based upon the locomotive's stall current.

Please see the related article (below).

Functions
You will choose a decoder based upon the number of functions which you want to operate on your locomotive.

The "2" series Digitrax decoders (such as DZ123, DH123 and others) have two functions, one for the front headlight and one for the rear. The "4" series Digitrax decoders (such as DZ143, DN143, and many others) have two additional functions (F1, F2), which can be used for additional headlights and such.

The "6" series Digitrax decoders (DN163, DH165 and many others) have an additional two functions (F1, F2, F3, F4).

The Installation
This can be a bit unnerving if you are "hard wiring" a decoder into place.

Wires are disconnected and the new connections from the decoder are soldered into place.

It is a matter of practice, but there are wire color standards so the connections are easier.

For a "2" series decoder:

  • Orange - Motor +
  • Gray - Motor -
  • Red - Power Pickup Engineer's Side
  • Black - Power Pickup Fireman's Side
  • White - Forward Headlight
  • Yellow - Rear Headlight
  • Blue - Common Connection for Headlights


If you are installing a "4" series decoder, the connections are the same, with the addition of:

  • Green - Function 1
  • Violet - Function 2


If you are installing a "6" series decoder, the same rules apply but you will need to check the decoder's instruction sheet for both the normal connections and for the additional function connections.

Motor Brush Isolation
It is Extremely Important that the motor brushes be isolated from any other connection than to the Orange and Gray wires of the decoder.

In most cases, this will not be an issue since most all modern locomotive models have been designed with DCC in mind.

However, older locomotives, especially the brass ones, frequently have a ground wire connection from one of the motor brushes to the frame of the locomotive.

Also, in some cases, one motor brush is grounded to the frame of the motor, which in turn is directly connected to the ground of the locomotive frame.

If you connect a decoder to such a motor without isolating the motor brushes, it will burn out the decoder.


Make sure that the motor brushes are isolated from anything else by using an ohmmeter with one connection on the individual motor brush and then touch the other ohmmeter connection to all other metal parts of the locomotive.

The Helping Hand
In addition to the Digitrax catalog, the Decoder Selection Guide and the Digitrax Tech Support Depot, your dealer may also be able to help you with the decoder selection and installation process.

Also, you may find that a Google search will turn up relevant information for your specific installation.

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