Consisting Problem

[NNeil]

I have two Atlas N-scale locomotives with Digitrax decoders, one DN163A0 and one DN163A2.

I've speed matched them so they run very close, but when I set up a consist, the speed of one of them is cut to a fraction of its normal settings. When I clear the consist, it runs normally again.

I figure that its probably a defective decoder, but I thought I'd check to see if anyone had some other ideas.

Neil

[arkansasrailfan]

I think you guessed it.

[jeffrey-wimberly]

Sounds like a decoder problem to me.

[Vail and Southwestern RR]

I'm not ready to jump on that bandwagon quite so fast!  But I need to go look at some docs.  Which one slows down?

[Paul3]

The only thing I can think of is that the 163 series decoders have a "switcher mode" that can be activated with F6 (but it has to be programmed).  This control mode reduces top speed by half, and therefore it's supposed to make switching easier.

Paul A. Cutler III
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Weather Or No Go New Haven
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[CSX Robert]

It doesn't sound like a decoder problem to me. Are you using advanced consisting and are you using BEMF compensation? When configuring the BEMF compensation on Digitrax decoders, there is a setting for when the engine is running by itself and when it is running in an advanced consist. The default setting is to turn the BEMF compensation off when in an advanced consist, which tends to cause an engine to run slower, especially at the lower end of the throttle.

[CSX Robert]

On Digitrax Fx3 decoders, CV54 controls Torque Compensation and Switching Speed Features(page 49 of the Digitrax Decoder Manual:http://www.digitrax.com/ftp/decodermanual.pdf). Torque compensation is not the same as BEMF compensation. Torque compensation makes up for the lack of low speed torque in the high frequency PWM motor drive. Digitrax's term for BEMF compensation is Scaleable Speed Stabilization, and it is controlled by CV55, 56, and 57(pages 58-60 of the decoder manual). CV57 controls the intensity of the BEMF compensation, and the upper 4 bits control the intensity when in an advanced consist and the lower 4 bits control the intensity when not in an advanced consist.

[NNeil]

Thank you for the help.  I set CV 57 to zero on the problem loco, reset the speed table, and the problem was solved.  The consist works perfectly now.

Neil