Back EMF/Digitrax

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Consisting Digitrax Multifunction Decoders with BEMF

When using Advanced Consisting, Digitrax multifunction decoders disable their BEMF. This occurs when CV19[1] is a non-zero value.

Digitrax splits the CV used for BEMF adjustments into segments for controlling the BEMF whether consisted or not. See the Digitrax Decoder manual for details.

Some Digitrax multifunction decoders employing CVs 55 – 57 (Scalable Speed Stabilization) may set CV57 to 0 (Off) when used as part of an Advanced Consist. This results in more throttle required to get the locomotive moving, creating conflicts within the consist.

Digitrax Variations

Digitrax provides several options:

  1. It can be turned on and off at will.
  2. A certain amount of tolerance can be programmed in – in two different ways (making it scalable); how much Back-EMF to use and how fast to use it.
  3. And lastly, they provide for two different amounts of Back-EMF to be used based upon whether the loco is consisted to another loco or not. This last feature allows you to program full Back-EMF control when not consisted, and have some tolerance for the other loco when consisted via Decoder-Assisted Consisting.

Like all things with versatility, Digitrax's Back-EMF is a little more complicated to program than others. Think about it. If can only be turned on or off, that's all you need to learn how to do. Digitrax's Back-EMF decoders can be operated in this manner. When running two locos together under Back-EMF control, it is necessary to learn how to program that feature into the decoders as well.

To do all of this, Digitrax uses three CVs (55, 56, & 57). To explain how each of these works, you must understand that the "target" speed is the speed with which the locomotive is supposed to be going according to the throttle setting.

  1. CV55 is used to tell the decoder how fast to compensate for speed differences.
  2. CV56 uses historical information to act as a shock absorber - to keep from over reacting.
  3. CV57 tells how much tolerance from the target speed is allowed.
    1. CV57 is divided in half. The first hex digit is for how much Back-EMF is applied when not consisted, the second digit controls the amount when consisted via Decoder-Assisted Consisting.
  1. CV19 is the consist address. If this is set, the vehicle will not respond to its primary or extended address.