Unusual (?) DCC question

[ndbprr]

I have one place that the PRR had a freight track in the center of North Philadelphia station that allowed freights to bypass the platforms and be rerouted back on to the respective track after passing the station. This track was bidirectional. Since the layout will be a big dogbone with the #1 & 2 tracks wired in a loop with the #3 & 4 tracks I have situation where I need to be able to reverse the polarity dependent on train direction on this track. Is there a device that would anticipate which direction the train is coming from and automatically adjust the polarity to the that track? My thought are to have a DPDT nonlatching switch requiring the engineer to hold it in the diretcion he is travelling. It will be about 10' long so this shouldn't be a problem or should I tie the track polarity to the switch points? any ideas?[:)]

[Kent]

Sounds like you need a reversing nodule.

Here a link to the Lenz one:
http://lenz.com/products/modules/lk100.htm
note, it's normally load in e frame so to see the page as it's meant to be seen goto:

http://lenz.com/products/modules/index.htm

And click on the LK100 link.

Hope this helps.

[ndbprr]

The problem that I see with a reversing module is it only senses polarity from one source and I need two sources.

[cacole]

With DCC, polarity of the track doesn't matter. Train direction is controlled by the decoder, not by track polarity. The only time you would need a reversing module is on a turn-around (reversing) loop or Y where a single track turns back on itself through a turnout. Since you say you're using a dogbone configuration, you will need a reversing module if the loop at the end of the dogbone turns a single mainline track back on itself; however, if the dogbone is a loop where two mainline tracks loop at the end, no reversing module will be required. Even then, a DPDT toggle switch can perform the same function as an expensive reversing module. To keep the wiring simple, connect the toggle switch to the loop at the end of the dogbone and reverse the polarity of it instead of the mainline. The only restrction will be that you will need to stop the train when you reverse the polarity using the toggle switch. Again, DCC doesn't care what polarity is on the track as long as it is the same on both sides of the turnout leg that the locomotive is going through at the time. Only one track needs to be insulated at the turnout.
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[dehusman]

QUOTE: Originally posted by ndbprr

The problem that I see with a reversing module is it only senses polarity from one source and I need two sources.

[dehusman]

With DCC you only have one source, the buss wires.

You are thinking DC wiring and its DCC. You have a buss of two wires which ALL the tracks are connected to. Since you have a loop, the inside rail is connected to one buss wire and the outside rail is connected to the other buss wire. For your reversing section, connect one reverser feeder wire to one buss and the the other feeder wire to the other buss. Then connect one output wire to one rail of the reversing section and the other output wire to the other rail of the reversing section. It doesn't matter how many entrances you have the reverser compares the polarity of the reversing scetion to the polarity of the main and changes the polarity to match.

[ndbprr]

I don't think the answers reflect the problem. Tracks #1 & 2 will be eastbound and tracks #3 & 4 will be westbound. I know DCC is AC but the passing track will be between tracks #2 & 3. In essence tracks 2 & 3 are the east and westbound legs of a loop. A train crossing from 2 to 3 or vice versa would short out identical to a reversing loop. Since the track between the two is bidirectional it needs to be able to be in agreement with either the eastbound direction or the westbound direction dependent on the train using it otherwise it will probably short out. That is the reason for using the DPDT switch and holding itin the direction of travel until the engines return to track 2 or 3. It would be nice if there is an electornic way of doing this so I could just leave it off the list for the engineers to take care of. The passing track definitely needs to be isolated the question is can DCC handle the assignment? I've tried to sketch it below so it makes more sense. there is also a loop at the west end.


_________________________________________________ ___
____\___________Track 3_________________________/___ Westbound _ I
\ \________________________________________ / / I I
\_/_________passing track_____________________\/ I ILoop
____/__/_____________________________________\__\___ _ I I
______/___________Track 2______________________\_____Eastbound___I

[Anonymous]

If I understand the problem correctly. Trains enter the passing track from the westbound inbound track, and then leave via the westbound outbound track. Or. Trains enter from the Eastbound inbound track and then exit via the Eastbound outbound track. So if you have on switch control point that selects either entry and exit from the westbound track . OR entry and exit from the eastbound tracks. Then, you could use a Double pole (DPDT) contacts on the switch machines that controls the route, the common input is to the passing track and the other contacts are connected to the corresponding alternative routes. This should would for both DCC and DC. With the DCC, both eastbound and westbound are from the same source and this would be a simple reversing wiring to the DPDT.

The end result would be that you use your DPDT switch idea. But move the DPDT to the switch contacts on either end of the passing track. Wire the control for the two switches in parallel so that the switches always work together, and there you go.

[ndbprr]

yeah, that would probably work the easiest. I was thinking along the lines of the passing track end switches being spring switches so they always funneled the trains in the right direction but that would work and probably is the easiest and cheapest to implement. Thanks

[dehusman]

I understand the problem. You are not understanding how the reverser and DCC works.

First off, you can wire all the tratracks (in both "directions") so that all the north rails are connected to one power lead and all the south rails are connected to the other power lead. then the loops on the ends of the layout would have reverser modules.
Or you can connect the input wires on the reverser module to the power leads on either main track adn the output ends to the center siding. No DPDT, it doesn't matter which of the four entrances you use. There are onely two options. Either the polarity of the center siding matches the polarity of the track the train is coming from or going to or the polarity of the center siding doesn't match the polarity of the track the train is coming from or going to. If the polarity matches the reverser does nothing. If the polarity doesn't match the reverser reverses the polarity in the center siding.

the major problem is the length of the center siding. If the center siding is less tha an train length long, there is the possibility that a metal wheel could cross the gaps on both ends at the same time. That would set up a situation where the polarity would both match and not match at the same time and the reverser wouldn't work.

Normally when you wire a DCC layout all the mainlines have the same "polarity" and that way you avoid the problems you are running into now.

[BR60103]

If you use the centre track only for bypassing the platform and not for changing from eastbound to westbound, the train length shouldn't be an issue.
What will happen is that when you enter the passing track from eastbound you get a microsecond short circuit and then the reverser flips the connections to the passing track to match the eastbound main. It will stay that way until you enter the passing track from the westbound and then the new short will cause it to flip the other way.
If you move through the passing track from the eastbound to the westbound, you will get a short as you exit and the reverse module will flip the connections to westbound.
You could pick one end of the passing track and use the extra contacts on the switch machine at that end to connect to the appropriate eastbound or westbound track. But you would not have the option of running out onto the opposing main.

[dehusman]

BR60103 said:
If you move through the passing track from the eastbound to the westbound, you will get a short as you exit and the reverse module will flip the connections to westbound.
You could pick one end of the passing track and use the extra contacts on the switch machine at that end to connect to the appropriate eastbound or westbound track. But you would not have the option of running out onto the opposing main.
==============================
Shouldn't make any difference whether you crossover or just pass. The reverser will match the polarity so there isn't a short. Think of it this way. If I have a 4x8 with aloop of track on it and then I add a reversing track across the middle, I can operate it in DCC with an auto reversing module. That is exactly what happens when a train crosses over in this case. Same exact schematic.
Don't need any DPDT switches or contacts on switch machines. Just hook up 4 wires.