Advanced consisting with digitrax decoders

[dbutters]

 I have recently installed a some Digitrax N scale decoders (DN163A0 and DN163A2) in a couple of my Atlas locos.  They run well on my NCE Power Pro system and I have reset CVs 2,5 and 6 so that they are as close to speed matched as I can get with a scale top speed of about 50mph.

I have tried running them in am 'old style' universal consist and they perform very well but when I try to run them as an advanced consist they run very poorly.  They will not accelerate and crawl along the track even at the highest speed step.

I have been doing a little research and I believe that the problem is related to the fact that the Back EMF function is not active for advanced consists unless I change CV57 from its factory default setting.

I read a post on another forum which suggested changing CV57 so that the value for consisted and unconsisted running are the same.  This means setting it to a value of 102 which is equivalent to x66 (hexadecimal) in order to be equivalent to the fatory default. (The left hand digit in the hex number is the  value for consisted operation and the right hand value is for non consisted operation.)

I would like to know what is actually causing this symptom when the back EMF is inactive in a consist.  If I set the level of BEMF to be the same as for non-consisted operation am I likely to get 'bucking'?  As yet I have not tried to run the locomotives coupled together so this is not a problem of one of them being set to travel the wrong direction.

Digitrax does not seem to be very supportive of the use of advanced consisting as all their online literature seems to direct users to use universal consisting instead.  Isn't advanced consisting more efficient because the command station doesn't have to send so much info.

Using universal consisting is also very limiting on an NCE system where there is a maximum number of 4 locos per universal consist.

[retsignalmtr]

I don't use advanced consist on my layout with the Digitrax Super Empire Builder and all Digitrax decoders. The only advantage I see with using it is so you can run more locos without using up so many address slots. I like to swap locos in consists so its easier to do with universal consisting. I have had 12 locos MU'ed together at one time with my system. How many trains can you run at one time? What is the number of addresses that your system can support at one time?

[rrinker]

 That is EXACTLY what is causing your problem, the settings for BEMF. You have your locos fine-tuned to run with whatever BEMF settings are there, but the defaults turn off BEMF when using advanced consisting, so defintiely the low speed operation is goign to get messed up.

 I can only suggest you try it. The default BEMF isn;t super-strong, there shouldn;t be too much bucking. If you have to reduce or turn off BEMF, then you'll have to retune the locos, mostly CV2 to get a reliable starting speed.

 I'm not particualrly fond of the Digitrax implementation of BEMF - there's a sudden speed jump at certain speed steps that you can mostly but not completely tune out with programming. That's why I use only TCS decoders now, they have autoamtic BEMF that fades out above a certain speed step (configured with a CV) so you can have BEMF for smooth starts but after your train gets rollign it cuts out so there'd be no bucking in consists.

                                                --Randy

 

[CSX Robert]

dbutters

...I would like to know what is actually causing this symptom when the back EMF is inactive in a consist...

FIrst of all, in case you do not know what bemf(back electromotive force) is, the decoder powers the motor using on and off pulses, and bemf is the voltage produce by the motor during those off pulses. When bemf compensation is not enabeld, the throttle setting is merely telling the decoder to output a certain amount of voltage. When bemf compensation is enabled, the throttle setting is telling the decoder to try to maintain a certain amount of bemf voltage from the decoder. As an example, without bemf enabled and evrything else set to defaults, you may have to advance the throttle several speed steps to have enough voltage to even get th eloco moving, whereas with bemf the decoder will automatically increase the voltage output enough to get the loco moving so that there is some bemf generated.

[CSX Robert]

rrinker

I'm not particualrly fond of the Digitrax implementation of BEMF - there's a sudden speed jump at certain speed steps that you can mostly but not completely tune out with programming. That's why I use only TCS decoders now, they have autoamtic BEMF that fades out above a certain speed step (configured with a CV) so you can have BEMF for smooth starts but after your train gets rollign it cuts out so there'd be no bucking in consists.

There is a slight speed jump at one point when using Digitrax's Bemf compensation, but I still prefer it over TCS's. Personally, I have been rather disappointed in TCS's BEMF compensation. It does not "fade out" above a certain speed step, it simply shuts off, and when I have tried to use that feature the loco will suddenly slow down, sometimes even stop, when I reach that speed step. Also, I can get better slow speed operation with Digitrax's Bemf than I can with TCS's "self-adjusting" bemf. What really bugs me athough is when I have it enabled and I try to adjust CV5 and 6 to speed match locos, I sometimes get odd results, such as instead of a linear progression of speed when advancing the throttle, the loco will slow down at certain throttle settings.

[rrinker]

 Hmm, I've not seen that so far in any of the ones I installed. And they have all, so far, just started right up on speed step 1 or 2 without any additional programming. I've put the TCS in P2K and Athearn locos (T1's), and Stewarts (T1 in a switcher and a DP2 in an AS16) and they all run great.

                                       --Randy