Consisting problems: Digitrax drop-in/plug-in decoders on NCE cabs

[OldEastRR]

My friend has tried consisting his 3 Kato F units w/drop-ins, and his 3 ScaleTrains GP30s w/plug-ins, all modern Digitrax, on my NCE layout but the process doesn't work.(two separate 3-loco consists) The engines all run very slowly at max speed setting, or don't run at all. We cancel the consist, reset the locos to CV8, and each one runs fine again. He has no trouble making consists at his RR club, but they have a Digitrax control system.
I've been able to make 2 consists of 2 locos, 2 of them have ESU, one a TCS, and one Digitrax decoders (only 1 digitrax decoder in my entire fleet). We've tried several times with his sets, carefully following the instruction manual, but no dice. Anybody know what's going on?
He's tried both the "advanced" and "brute force" methods on NCE.

[peteski]

After you tried to create that consist have you tried separating all the locomotives and spacing them a foot or two on the track then running the consist to see what the specific loco speeds are?  That might present a clues to what's going on.

I don't think NCE does anything funky with the speed steps coming from the throttle or command station when the locos are consisted.

One thing that stands out to me is if you are using advanced consist (CV19) with any Digitrax decoders, they have separate BEMF set of parameters which will affect their speed.

I'm also curious why you ended up resetting the decoders for breaking up consists?  Wouldn't breaking up a standard or advancing consist (using the NCE throttle) be enough to restore their individual settings before consisting?

[Maletrain]

Peteski's comment about Digitrax decoders making changes to speed control when in a consist are definitely worth looking into by seeing how the individual locos behave when in a consist but not coupled together.  The Digitrax decoder loco might be getting dragged.  Or, there may be other problems that test would reveal.

An additional thought is whether your friend uses light bulbs to limit the current to his NCE track.  If so, six locos might be drawing enough current to pull down the voltage due to increased resistance in the bulb. 

For that matter, insufficiently low resistance in the track feed might do the same thing.  You can check for that with a light bulb that draws about 1 amp at 12 volts.  Use that bulb to short across the tracks, and use a volt meter to see what the voltage is across the tracks nearby while the bub is lit.

[OldEastRR]

For my friend's units: we separated the three locos and when we activated the consist all 3 ran verrrrrry slowly, even at top speed setting. And then only 2 ran, one sat there. Very weird.

[John]

The first thing I would do is check the programming on these decoders .. make sure Vmax or the speed tables haven't been changed ..

also measure the voltage across the rails .. a VOM set to AC will get you close enough .. if it's not over 10-12v you have an electrical problem

[bbussey]

It has something to do with the Digitrax decoders. I ran into the same issue with Digitrax drop-ins in an A-B-B-A set of InterMountain FTs. They won’t run over a crawl speed when consisted on my NCE system, yet they run fine as individuals. Other non-Digitrax four-unit consists run with no issue, including two sets of FAs/FBs. I’m in the process of swapping out the Digitrax decoders for ESU decoders.

[peteski]

Bryan, we had a lengthy discussion  explaining the behavior of Digitrax decoders and the BEMF while in advanced consist.  They have the unique feature to have 2 sets of BEMF parameters. One for "normal" operation, and second one for when in advanced consist.  BEMF settings affect the models running (and its speed). This is all described in details in https://www.therailwire.net/forum/index.php?topic=59009.0