Engine on DCS variable track starts at full speed

John,

I've had the same issue.  In my case, it appeared to be tied to having the variable channels set to variable.  I use DCS 90+% of the time so I set my variable channels to fixed and only set them to variable if necessary. With the variable channels set to fixed, the problem is gone.
I haven't had this issue in quite a while but when I was going through things, I started doing conventional resets on all my engines.  I then tested each on in conventional just to be sure when it comes up, it doesn't move.  I had a premier K4 that I had to set in conventional neutral or it would take off like you describe every time it missed the DCS Watchdog signal.

Tony V

I have been setting my variable channels to fixed for years.  You don't have to do any reconfiguration to use them in variable mode, just select the track and start using the thumbwheel to control the voltage, they automatically switch to variable mode.

Interesting. I've heard of the ability to set a variable channel to a fixed mode, but Ive never really looked into it heavily. Perhaps this is the solution.

A question about doing that: Does the new circuit behave exactly like a fixed output in every way? For example, the variable tracks start up at zero volts when you turn on the system. Will they now start at the maximum?

Also, since the circuit in particular is a siding, there are times when I do want to shut power down to that section of track. Is there still a way to do this, perhaps with a toggle button of off or on?

Q: Does the new circuit behave exactly like a fixed output in every way? For example, the variable tracks start up at zero volts when you turn on the system. Will they now start at the maximum? 
A: Yes.  The setting is in the TIU setup section in the remote or app.

Q: Also, since the circuit in particular is a siding, there are times when I do want to shut power down to that section of track. Is there still a way to do this, perhaps with a toggle button of off or on?
A: Not exactly.  When a track is powered up, the TIU sends a watch dog signal to DCS equipment to initiate DCS communications.  The watch dog signal only happens for ~30 seconds.  If if you interrupt track power with a toggle switch, when you re-apply power the power will come back but no watch dog signal is generated.  This can cause the run-aways like you have experienced.  There are a couple of options to fix that problem.  Search for "TIU" and "Passive" and that should provide a few threads that discusses the options.  I also believe Gunrunnerjohn (replied above) has a circuit that can help with the watchdog signal in the scenario you call out.

Tony V

I have run into the same issue as JOHN M.

Using the variable channels in Variable mode, I wanted to be able to cut power to my tracks with the remote. I left them in VARIABLE mode and set the startup voltage to 22. Now with one click of the wheel, I have max power out to my tracks. Well, this didn't work as well as expected. At random times engines would miss the watchdog signal and start up in conventional mode on their own.

My workaround was to set the startup voltages on my variable channels to 21.5. Now it takes two clicks to achieve max voltage to the tracks but my engines never miss the watchdog signal. I don't why this works but it does.

I haven't done a deep dive into the issue but I can also confirm this happens if I have a short and my power bricks trip breakers. After correcting the short and resetting the breaker power comes on instantly to full voltage and occasionally my engines will miss the watchdog signal again.

@VonFrank posted:

Interesting. I've heard of the ability to set a variable channel to a fixed mode, but Ive never really looked into it heavily. Perhaps this is the solution.

A question about doing that: Does the new circuit behave exactly like a fixed output in every way? For example, the variable tracks start up at zero volts when you turn on the system. Will they now start at the maximum?

Also, since the circuit in particular is a siding, there are times when I do want to shut power down to that section of track. Is there still a way to do this, perhaps with a toggle button of off or on?

Yes, when you turn on the power to that  TIU channel, it'll come up at full voltage.

For sidings you have a little issue to deal with, that being the lack of a watchdog signal when you turn off the power to the track but not the input power to the channel.  The only time the TIU generates a watchdog signal is when you first power up a channel.

You have probably seen discussions about the Watchdog Generator project, that's a DCS Remote Commander fitted with an auxiliary timer to generate continuous watchdog signals on the track.  I use them on all four channels of my TIU so that I always have a watchdog signal on all the tracks all the time.

If your variable channels are solely for the sidings, have a toggle switch in the power feeding the variable channel. when you power on the sidings you will also power the variable channel and get a watchdog signal.

That only works if you want to apply power to all sidings at once.  Typically, you want to only power up the siding you are currently using.

I just  use the input switch to the TIU channel as a master powering the siding switches. I switch on the desired siding and then turn on the switch powering the variable channel. The selected siding then gets the watchdog.

So I set the siding track to FIXED mode in the DCS settings, and so far it seems to work. The track goes live with power when the transformer is throttled up (just like the other fixed lines) and I have not had the unexpected start-ups or runaways since doing so.

Big thanks to everyone who offered their recommendations!

So even if an engine misses the watchdog signal and comes up in conventional mode shouldn't the engines start up in neutral? Isn't there a way to set that?

It should start in neutral.  However, sound and smoke all come on, which is probably undesirable, depending on how many yard tracks you have off the one TIU channel.  Also, sometimes there's a double-tap in the power on and engines take off.  I know I've seen that happen, and I think it's a PITA to have all the sounds, lights, and smoke come on in the whole yard!

The lights are a pain i suppose, and yeah, a double tap in power to make them switch into gear would suck.

I wonder if a neutral direction lock would work.

The sounds and smoke are an easy solve, just turn the smoke and volume pots to OFF.

Yep, I have all my DCS engines smoke turned off for conventional.  I leave the sound on so I can tell that it came up in conventional mode.  I want to know because a power cycle at that point is not a good thing, it will take off!

Bottom line, everyone has their level of tolerance for stuff like this.  Since I can pretty easily solve it with the WD generator, that's how I did mine.

After having DCS for since the early 2000s, I finally turned my variable channels to fixed today after reading this thread.  I'm never going back. You can still vary the voltage on the variable tracks and run conventional. I just had a great multi engine/conventional/command run session.  I wish I did this earlier. Thanks @gunrunnerjohn for the tip.

@Strap Hanger posted:

After having DCS for since the early 2000s, I finally turned my variable channels to fixed today after reading this thread.  I'm never going back. You can still vary the voltage on the variable tracks and run conventional. I just had a great multi engine/conventional/command run session.  I wish I did this earlier. Thanks @gunrunnerjohn for the tip.

Yep, the only thing that FIXED does is start out with voltage at full input voltage when the channel first receives power.

There is one downside if you are a regular conventional runner.  It's exactly what I said above, as soon as that channel input is powered, the power comes straight through.  In VARIABLE mode, the channel comes up with zero volts when the input receives power.  No big deal, but it may be a reason for some folks to leave them in variable mode.