# Advance Consisting, Digitrax DN135 and Bachman HO GP9 (DCC) pairing.



## Joefrumjersey (Apr 16, 2013)

My issue concerns two identical Bachmann GP9s of the same series with Bachmann Factory Installed decoders replaced with Digitrax DN135 decoders. Both decoders are programed the same: Cv2 =2; CV3=1; CV4=1; CV5=154; CV6=128. One unit has reversed polarity CV29=35. Programing was done on the main, using MRC Prodigy Advanced system. (CV29 value per MRC PA²manual).

Individually, these locomotives perform quite nicely at 128 speed step setting, crawling at SS#1 and gradually increasing speed at a rate and level comparable to other units. When controlled independently by two separate throttles, they maintain distance very well, and exhibit great speed matching, which varies slightly speed step to speed step – one will be slightly faster at a given speed step, but resynchronize at the next speed step. There is no issue here.
However, when the two engines are consisted, using the MR C PA² Advanced Consisting – which is supported by Digitrax per the Digitrax Manual – they do not perform or sync well at all.

Both motors are energized at speed step 001, but will not move until throttle is advanced to a range of speed step 020 -027. Then one will move before the other, and at a higher rate of speed than the other. There is no apparent synchronization until the throttle is advanced to somewhere around speed step 040. Even at that point synchronization is erratic. One unit seems to be doing all the work, while the other is pushed or pulled around. 

In other words, It appears that the two units consisted and controlled by one throttle, require a greater current draw than the two units operated separately on the same track, controlled by separate control cabs. Which, of course, makes no sense.

Using the 28 speed step mode, does not improve the situation. The units will not move until around speed step 05, and will reach operating speed at about speed step 10, but with erratic synchronization.

I previously noticed this with a consist of a Bachmann RS3, and a Bachmann GP7. Again both with unmodified Bachman mechanism and use of DN135 decoders replacing Bachmann’s factory installed decoder. 

I used the same consisting method, pairing Atlas with Atlas, P2K with P2K, Athearn Genesis with Athearn Genesis , – and Atlas + P2K with satisfactory results. These consists include locos using Digitrax, NCE, TCS, and Tsunami decoders, with both matched and brand mixed consists.

The only common point here is the Bachmann equipment / Digitrax decoder combination, but in all cases, the response to throttle settings with single not consisted engines is excellent. Performance only declines when the engines are placed in consist.

I appreciate any feedback, insight, or solutions.


----------



## DonR (Oct 18, 2012)

Joe

You got some odd carryings on there.

The Digitrax and other DCC gurus will surely have
some word for you.

I have a question. Did you try consisting the Bachmann
GPs when the Bachmann DECODERS were still in use?

Reason for question. We consisted two Bachmann GPs last week...Bachmann
DECODERS. Good speed match and pulling power.

I regularly consist 2 GE 70 tonners with Bachmann DECODERS
and get good speed and power match.

Maybe they just don't like the competition moving in.

Don


----------



## Joefrumjersey (Apr 16, 2013)

DonR said:


> Joe
> 
> 
> I have a question. Did you try consisting the Bachmann
> ...


Answer to question. When I obtained my first DCC equipped standard line Bachmann, the decoder that came with the GP7 wasn't so good, so I found it had an 8 pin plug, and substituted the Digitrax. Worked so well that now I automatically replace all OEM decoders in this line with DN 135 decoders. 

BTW: I placed this question on several forums and then contacted Digitrax Tech support. FYI: the fix is to disable back EMF. Digitrax recommended setting CV 57 to a value of 102.
The fix worked. 

Joe


----------



## mopac (Feb 24, 2011)

Glad you got a fix. I thought back emf was for consisting. I have not
consisted yet ( no layout) so I know nothing about it. Looking forward
to running 2 or 3 engines lashed up together. Thanks for the info. Hard
to remember all the info I get here. I try to write some down but a month
later can't make heads or tails or can't find the piece of paper.


----------

