Is There Such a Thing As Automated DCC Operation?

[guslcp]

Most (I'm 99% sure all...) D'trax decoders have the option to enable DC response.  I believe it's one of the many default settings on the decoders.  To accomplish what you want, use the DC section in front of your platform and any engine that gets into the station will come SMOOTHLY to a stop.  The DC section would need to be wired from a DPDT toggle switch, so to get the train going again, you would switch to DCC and the train would  SMOOTHLY start up again.  Or you can use one of the many relay setups described by others....Once out of the station you set the toggle switch to DC which will activate the same response whenever another train enters the DC section, or leave it on DCC so any trains you don't want to stop, don't.  The acceleration and deceleration settings you have set up on your CV's will work just the same way as when you turn down the throttle....

[Jim Banner]

An excellent suggestion from Hunt, as usual.

After doing some perusing of manuals myself, I came across another way of creating a stopping block.  It is under the title Brake Generator Example on page 33 of the Digitrax Decoder Manual.  The manual can be download in pdf format by clicking on this link:

http://www.digitrax.com/ftp/decodermanual.pdf

I think what we are heading toward is a low cost system with a magnet on the locomotive you want to stop or on the specific car you want to stop.  When the magnet passes a reed switch, the closure of the reed switch starts a timer which pulls in a relay.  The relay switches a section of track from DCC power to dc power, causing the locomotive to decelerate smoothly to a stop.  After the timer runs out, the relay drops out, switching the section of track back to DCC and the locomotive smoothly accelerates back up to speed.  If you are interested in having different kinds of cars stop at different places, there are at least four suitable locations for magnets - top left side, top right side, bottom left side, bottom right side, in all cases hidden inside the car.

Note to BradKT - There is no need to rip up any trackwork to create an isolated section.  Just add some gaps, typically four.  If you use E-Z Track, all you need is an Atlas hobby saw to cut through the rail joiners between two sections.  Then slip some paper in the gaps and saturate the paper with ACC.  The next day, you can trim the paper flush with the rail heads and file smooth.  The paper is to keep the rail ends from touching.  You do not need insulated joiners if the base of the track is nailed/glued/screwed in place.  If your track is NOT firmly in place, cut the gaps in the center of a section.  Apply the paper as above.  The ties and base will hold the rails in alignment.  My own H0 layout has been rewired several times over the decades and each time seemed to require a different scheme of gapping.  So I would just electrically bypass old gaps and cut new ones.  There are well over a hundred cut gaps in it and none of them cause any trouble.

Jim

p.s.  looks like guslcp has been reading the same manual.

J.

[guslcp]

I had to...
About a month ago I got a hankerin' to run some of my older DC locos, some that won't ever see a decoder.  Since I hate to run them on DCC track because of that awful buzzing and whining I decided to make the layout DC/DCC, but in order to not have to remove the DCC engines that would have responded to DC as well, I had to figure out how to disable the DC feature on my decoders.  Took longer to do that than to actually disable all the locos....

[mabloodhound]

So now, just one more question.   What happens to the sound when the loco enters the DC and comes to a stop.   For example, with a Tsunami steam card, does the engine sounds still work when sitting in the station?

[Jim Banner]

The Tsunami would still have power and it is designed to work on both dc and DCC so I suspect it would.  I don't remember that being covered in the manual but a call to Soundtraxx should get you a definitive answer.  Let the rest of us know what they have to say.

Jim

[BradKT]

The one thing that I like about these discussion threads is that they do get the thinkers to come out of the woodwork and actually come up with some very creative solutions.  I understand what Jim Banner said about isolating the track.  I am still not too clear on how to make an isolated section of track go from DCC to DC and back again, but I am going to read the referenced section of the Digitrax manual.

Even if I don't make these changes now, I'm going to save this thread for further reference.

[NarrowMinded]

Here's one way to do it. if you get a DPDT relay with the same voltage as your dc supply you could use that to power the relay.

Any and everybody feel free to comment, and copy and change the image anyway you want.

NM

[Jim Banner]

Your picture is worth a thousand of my words.  The only thing I would change is that I would put the train detectors inside the isolated section rather than outside it.  This is because you really don't want the isolated section switching to dc power before the locomotive arrives, otherwise the wheels of the locomotive and/or any other metal wheels may connect the output of the dc supply to the output of the DCC supply with unwanted results.

When you connect a DCC booster and a dc supply in parallel, either on purpose or accidentally as above, there is a problem with one of them being dc and the other ac.  On one half cycle of the DCC waveform, the two supplies are matched in polarity and little or no current will flow between them.  But on the other half cycle, their polarities are opposite which is the same as saying they are connected in series with no load to limit the current.  The most likely result would be that the DCC booster would cut in and out but that the current each time it cut in would be high enough to destroy the electronics in the dc supply.  Theoretically, a dc supply with electronic current limiting would take care of this, but I have not tried this in practice.  Note that this current limiting is different than the circuit breaker normally found in a model railroad power back.  Rather than interrupt the circuit when the current exceeds some limit for some length of time, an electronic current limiter never lets the current get higher than the limit in the first place.  Note also the use of the term "booster."  It refers not only to an add on booster connected to the DCC command station but also the booster often built into a command station.  It is easy to forget that a unit like the E-Z Commander is really a throttle, a command station and a booster all integrated into one neat package.

The problems are not insurmountable.  The easiest solution is to make the isolated stopping track long enough.  This is easy with a freight train using all plastic wheels except the locomotive(s).  Then the stopping track needs to be the length of the locomotive(s) plus the stopping distance plus a bit more for safety.  But a passenger train with all lighted cars would require a stopping track a train length long plus plus the stopping distance plus a bit more for safety.  One might think at this point that a freight train will all metal wheels would have to have a stopping track longer than the train, just like the lighted passenger train, but here there is another way out.  A dead (never powered) isolated section longer than the longest freight truck when placed at the beginning of the stopping track will let diesels and steamers with driver and tender pickups through but will not allow individual wheels or trucks to short between the main line and the stopping section.

Jim

[NarrowMinded]

Hi. Jim,
my first drawing had the detectors inside the gaps, but then I thought of the momentary loss of power when the relay flips. I thought maybe as long as the DC voltage was set the same as the dcc voltage, the decoder might not see it as DC until the last pickup leaves the dcc track.

Being  non dcc educated I didn't know how the decoder would react with these two flavors in parallel. I didn't know DCC was AC on the tracks either.

Could diodes placed on the DC output protect the DC from the series condition caused by the wave form?

And another crazy thought with out all the facts. What would happen if instead of switching to a separate DC supply,  you use the relay to switch  the DCC through a bridge rectifier changing it from ac to dc?

Just curious about all of it. I know the simple thing would be to have the whole consist on the isolated stop section as you mentioned.

I think of all these little bits of knowledge like spices, once in a while when I am cooking something up all I need is a pinch of this or that to make it turn out delicious. and then theres the times it burst into flames and sets off the smoke detector.

NM

[Jim Banner]

A diode in the output of the dc supply would protect the dc supply from reverse current during the half cycles when the DCC and the dc were the same polarity, if the voltage of the DCC was higher than the dc.  It would not help on the other half cycles when the DCC booster was trying to suck too much power out of the dc supply.

Using a bridge rectifier to generate the dc from the DCC would have several advantages, including guaranteeing that the dc and DCC voltages matched.  But you would still have to avoid shorting the dc output of the bridge back to the DCC of the bridge because you would still have a dead short on every other half cycle.  The only difference would be that the short was through a diode.  But if such a short did occur, then the protection circuits in the booster would protect both the DCC and the dc sources because they are both being drawn from the same source.  That is a very nice simplification of the dc source.

I wouldn't want these bits of knowledge to be too much like spices - having them burst into flames and smoke inside your head and all ...

Jim

[NarrowMinded]

I have a bachmann on30 rail truck due for delivery on Monday it will be my first unit with dcc installed if it has the stop on DC feature I am going to take the plunge and buy a dcc system and give the automation a test run. I have all the parts for the automation circuit in my parts bins. If all goes as expected I will post a picture of the circuit and a list of parts.

NM

[mabloodhound]

Hey, NM, if all goes well, what about posting a video in action? 

[NarrowMinded]

Sure I'll post one if all goes well
NM

[NarrowMinded]

Well.. Railtrucks lost in the mail. Some how walthers sent it to the wrong house number, they say there's nothing they can do. And want me to reorder it, and they will credit me once it returns to them if ever. Checked page I copied when ordering has my correct address, how is it my fault? First and last time I order from walthers.

Sorry had to rant here sense I was going to experiment with the automation on the rail truck

NM

[poliss]

Write a letter (not email) of complaint to the President and CEO of the company. I usually find that gets results.