KB509: Narrow Gauge Decoder Selection

This article was last updated on Sept. 3, 2011, 1:31 p.m. | Print Article | Leave Feedback

Q:  As an HOn3 advocate and new to DCC with early PFM engines (2-6-0 & 2-8-0 motors in tender and some smaller ones) what would be the suggested decoder (am not sure am identifying the part correctly) that would be used in these engines? All I have seen so far identifies items used in H0 standard gauge.

A:  Digitrax has many happy Narrow Gauge customers.  You'll need to consider three things to join their ranks.

1.  The physical size of the decoder, because narrow gauge engines are smaller than Standard Gauge locomotives.
Since your space is limited, using smaller decoders is the solution.
Digitrax DN decoders are made to fit in N-Scale and larger locomotives. They are rated at 1.0-1.5 amps.  Digitrax DZ decoders are made to fit in Z-Scale and larger locomotives. They are rated at 1.0-1.25 amps.
We recommend using the wired versions of the decoders unless your locomotive is equipped with a DCC socket. 

2.  The power consumption of your particular locomotive. Most modern can motors draw less than 1.5 amps when stalled.  If your loco has a can motor, any of the Digitrax decoders that will physically fit in your loco should work just fine.

In the case of older brass locomotives, which have open frame motors that need greater power than more modern can motors, you will need to check the stall current before deciding on a decoder to use. Because of these motors, many brass locomotives look wonderful on the shelf but are not so wonderful in actual operation.  Open frame motors tend to have operating problems and consume more power, creating heat build up inside the locomotive.

Many PFM engines were very well built with high quality open frame motors, so the mechanism and motor may not consume as much power, so the smaller decoders will likely be sufficient. To be safe, you should measure the stall current before choosing a decoder to install.

A locomotive's stall current is measured by running the track voltage up to full power with the motor being held so that it will not turn. This value tells you how much current the decoder must be able to handle for successful long term operation.

3.  It is very important that the motor brushes be totally isolated from the frameto avoid permanent damage to the decoder.  This is true of every DCC decoder installation.  The issue with narrow gauge locomotives is that many more of them are brass with open frame motors.  So, you have to check your loco before doing the install. In many cases, one brush of the open frame motor is grounded grounded to the chassis, a sure recipe for fried decoder.

If you have a locomotive with an open frame motor, we recommend re-motoring with a modern can motor to avoid these issues.

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