(This is a question I have sent off to NCE about my decoders. I do believe the problem rests with the decoder…not a premium model, granted…and not with the command station or something else. However, I would be delighted to be proved wrong and would appreciate any forum members experience and advice.)
"I have a problem a that has been with me ever since starting DCC about 7 years ago. I use a Digitrax command system with a DCS 50 Zephyr throttle and another radio and IR remote throttle…though I believe the problem is with the NCE decoders…of which I have over one hundred and nine installed in various locomotives (you see I am a good customer)
Almost all of the 109 are D13SR or SRJ. The problem is that when a loco derails and begins to short out, and I then I power off the track and attempt to move the loco…either lifting it completely off the track or altering its position, I can set off 3 or 4 or more locos on the track all running at full speed in reverse. I then have to react really quickly and go the wall switch to kill the power to the command station.
The problem does not seem to affect other decoders. Just now it happened, and several Soundtraxx Tsunami decoder-equipped locos, which had been the previously used model on the throttle, sat still while 4 locos with D13SRs took off in reverse, including a pair in a consisted address.
Can you explain this, and a possible remedy. I know this particular model of decoder is not premium end, but I am well pleased with them in other regards…especially the price as I have had so many to install in my layout.
It is a nuisance to have to kill the power generally since the fastest method for me (and I have to be very fast to avoid dumping locos into the turntable pit or running them off the end of spurs etc.) is to also kill the power to every other part of the layout…accessories, etc. with a wall kill switch. "
Turning off Analog Conversion is always a good idea. The real problem that is causing this may be your wiring connections. Loose track connections & bad feeders can induce ‘noise’ onto the track confusing the decoders. I had this issue with my ‘test track’ made of Bachmann EZ Track - Soldering the connections resolved the issue. My layout has a #14 bus with feeders to every section of rail - No problems.
Yes, that analog conversion CD came to my mind too…because it is how I resolved the issue on a particular loco another time…So I am going to turn it off a half dozen locos on the layout now and purposely try to make them take off on me. I’ll let you know.
I have all locos on analog so that I can easily run them in the shop on my cleaner system…but I will have to just turn them all off. Besides, I now have another cleaning station on my staging area that they can run DCC on.
Good idea about track connections. I also left nothing to chance…I have soldered entirely and also drop feeders every three feet at least. But one never knows.
DCC decoders constantly run through a set of check sums. They do this hundreds of times per second checking for any information changes. One of those checks is determining what type of voltage / signal the decoder is receiving. If it does not detect a DCC signal, it automatically assumes it’s running on DC - that’s how you are able to run your decoder equipped engine on DC without having to manually change anything.
During a power interuption or even a short, there is an interuption in the DCC signal. If it happens during the exact time the decoder is going through the check sum sequence for track voltage and it doesn’t see the DCC signal, it will assume it’s on DC and take off at full speed with the voltage that is on the rails.
By turning off the DC enable in CV29, you are taking that option out of the check sum sequence, so the decoder is never looking for anything but a DCC signal. A DC signal will just be ignored.
Thanks very much Mark. That makes sense. It is also what the NCE support team emailed me just prior to reading your response. Together the two messages make perfect sense. NCE also mentioned “snubbers” on the track bus being a good idea, and I am going to read their info on that now.
99.9% of the time, turning off the DC enable in CV29 will cure this problem. The snubbers on the end of your DCC buss are really only beneficial if you have a really long buss run.
Years ago when I first installed my DCC system, I had the same problems. Turning off DC enable on all my engines cured the problem 100%. My longest buss run is well over thirty feet and I have no snubbers at the ends of any of them.
You probably don’t need the snubbers. Have never found the need for snubbers on a Digitrax layout. When the bus gets out to about 25+ feet frm an NCE booster, the snubbers help.
One issue I found is that the Digitrax UT4 throttle is sending spurious data to the Loconet bus. I just started having this problem on a Digitrax decoder and had to unplug the UT4 for good and the problem stopped. Of course have CV29 turned off for most of my locos.