Reverse loops in DCC

Markku

Markku

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Hi all,

Being grown in Märklin-land, I have been totally ignorant about any reverse loop problems. But now that I'm getting myself familiar with two-rail garden railways I have some questions.

For analog (DC), I think I understand the case: in LGB they have the suitable special pieces of track (containing diodes and whatever) that make it possible to ride through the loop (stopping in the middle or something like that...). But as an IT engineer I'm not so interested in analog so digital would be my choice (I think at the moment at least!).

In digital (DCC) I see there are specific reverse loop modules ("autoreverser"?) in LGB and Massoth at least, and they are connected with sensor setup or to detect the short-circuits caused by the rolling stock running over the isolations. (I've read the LGB 55085 manual from MTS Reverse Loop Module | Märklin.) Fair enough. But my questions are:
  1. Are these DCC reverse loop modules somehow dependent on the central station details? I mean, if I choose the wonderfully cheap ML-Train central station, can I use those LGB or Massoth reverse loop modules with it? (I haven't yet decided the CS but it depends on the pricing, availability, features, etc.; I will ask about those in a separate thread some day...)
  2. For the two setup modes (sensors or short-circuit detection), are there some specific pros/cons that I should be aware of? From the LGB module manual I see that the wiring for the short-circuit detection is much simpler so that's a pro for that option I think.
  3. If I have two or more loops, can I use the same module for all those loops? Does it then matter how many trains are in the loops at the same time or so?
  4. Is it a thing that the switch operation (the switch that joins the loop; or is it a "point"... in Finnish it is "vaihde" :D) can/should/must be integrated with the reverse loop controls somehow? Or was it just some analog kludge.
If you think there is something else that I may miss, feel free to comment other things as well. I've tried to read at least the more recent threads about the reverse loops here. Thanks for any comments.
 
I'll give a quick answer to a couple of your questions. I've got to leave for my golf league in a few minutes!

1. The LGB and Massoth Reverse Loop Modules operate independently from the central station/booster and can be used with any DCC (or mfx) digital system. I'm not sure about other manufacturer's modules, you need to look at their instruction manuals.

4. Unlike the LGB reverse loop track sections for analog layouts, a DCC reverse loop can be entered from either branch. It is completely independent from the turnout. You may want to hook up some arrangement to throw the turnout after the train has cleared but it is not necessary. You do not need to do anything with regard to controlling the loco either. It will just continue on its way around the loop - unless you want it to do otherwise.
 
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2. Short circuit mode is good enough but they added the sensor option in an attempt to make things kinder.
3. You should have 1 module per loop. Trains can then enter any loop at any time.
 
Finally answering point 3 only 1 train should be moving in the reverse section at one time as if another exits it will detect the short and reverse the poser thus likely causing a second train an issue. Also a Train MUST be completely inside the loop before it attempts to exit if there are metal wheels on all the stock or just front and rear as the detector would again detect a short situation at each end of the loop and likely throw a wobbler.

However I believe that I am right in saying this, if you had a set of double ended sidings wholly inside the reverse loop and stopped trains in the siding ps and started up a different one that should be Ok? Have to say I have never tried this option.
 
Let me respond to what Jon is saying in post 4. I've often operated with more than one train in my reversing segment. I'm using a LGB 55085 reverse loop module with sensors. Everything works fine as long as only one boundary between the reversing segment and the rest of the layout is bridged at a time. The change in polarity in the reversing segment does not cause any problem with other locos/trains with metal wheelset as long as they are wholly within the reversing segment. They are just like the train that that triggered the reverse module whose loco decoder is subjected to a sudden shift in polarity. I have verified this with three locos, two already operating in the reversing segment and a third entering the segment and causing a polarity shift. This was followed by a second polarity shift when one of the locos exited the reversing segment. There were no noticeable effects in the running of any of the three locos. I purposely chose locos with decoders by three different manufacturers, one Massoth Onboard XLS, one ESU XL v.4, and one Märklin mfx for the test to see if that made a difference. It did not.

What this verified is that you can have a yard wholly within the reversing segment and a loco operating in the yard will be unaffected by another train passing through the reversing segment. The polarity shift does nothing to upset its decoder.

You will note that I use the term "reversing segment" rather than reverse loop as it is more general and applies to my situation which involves a wye junction.

Also, you must be aware of the current limit of the reversing module and use appropriately sized wire for the power in/out connections. The Massoth 8157001 unit is limited to 8 amps continuous and 16 amps surge in the reversing segment. I assume this is also true for the LGB 55085 module (manufactured by Massoth). The sensor wires can be a smaller gauge diameter.

One other thing to be aware of with regard to the Massoth reverse loop module. Massoth warns on page 7 of the manual that their module can only be used in sensor mode with short circuit sensing disabled (jumper in place) if there are more than one reverse loop modules on the layout. Again, I assume this is also true of the LGB module although the LGB 55085 manual has no such caution.
 
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Thanks for the answers and comments. My initial feeling is that I may go mostly with LGB products as I have a local supplier in Helsinki. Other brands will require ordering from f.ex. Central Europe, so that always causes some unknown factors.

Phil, your last point about using only sensor mode if multiple reverse modules are present is interesting (in the literal meaning), I guess I have to remember that if I consider using two loops for some reason.

Also, the current limit is apparently something that needs to be considered...
 
Yes, the sensor mode only stipulation by Massoth when multiple reverse loop modules are being used in the layout is interesting. I had actually forgotten about the warning until I re-read the Massoth manual today! I don't know why this is the case, but if Massoth says it is so I wont argue the point. I know the same is not true of some other short circuit sensing reverse loop modules such as the DCC Specialities PSX-AR which is widely used in the U.S.
 
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phils2um said:
Let me respond to what Jon is saying in post 4. I've often operated with more than one train in my reversing segment. I'm using a LGB 55085 reverse loop module with sensors. Everything works fine as long as only one boundary between the reversing segment and the rest of the layout is bridged at a time. The change in polarity in the reversing segment does not cause any problem with other locos/trains with metal wheelset as long as they are wholly within the reversing segment. They are just like the train that that triggered the reverse module whose loco decoder is subjected to a sudden shift in polarity. I have verified this with three locos, two already operating in the reversing segment and a third entering the segment and causing a polarity shift. This was followed by a second polarity shift when one of the locos exited the reversing segment. There were no noticeable effects in the running of any of the three locos. I purposely chose locos with decoders by three different manufacturers, one Massoth Onboard XLS, one ESU XL v.4, and one Märklin mfx for the test to see if that made a difference. It did not.

What this verified is that you can have a yard wholly within the reversing segment and a loco operating in the yard will be unaffected by another train passing through the reversing segment. The polarity shift does nothing to upset its decoder.

You will note that I use the term "reversing segment" rather than reverse loop as it is more general and applies to my situation which involves a wye junction.

Also, you must be aware of the current limit of the reversing module and use appropriately sized wire for the power in/out connections. The Massoth 8157001 unit is limited to 8 amps continuous and 16 amps surge in the reversing segment. I assume this is also true for the LGB 55085 module (manufactured by Massoth). The sensor wires can be a smaller gauge diameter.

One other thing to be aware of with regard to the Massoth reverse loop module. Massoth warns on page 7 of the manual that their module can only be used in sensor mode with short circuit sensing disabled (jumper in place) if there are more than one reverse loop modules on the layout. Again, I assume this is also true of the LGB module although the LGB 55085 manual has no such caution.
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Thanks for that explanation Phil. Never having deliberately tried out the multiple option of trains with a reverse loop it is interesting that it can be done providing the basic rule of only 1 making the reverse (or should it be called swop?) change at a time. The main place that we had reverse section modules was on Andrew Rush’s Ruschbahn and we occasionally ran foul of a full short which I guess was when we were attempting to run a train in and out of the reverse loop at the same time. Yes it may have happened. On my own small fumblings with a triangle (wye in US) to get my head round the workings of the LGB module I used LGB R1’s for the test set up and not much more than an engine was suitable for that testing.


Posted this link again as it may help Markku a little.
 
Jon and others - I need to emphasize that I am using sensor only mode in my reverse loop module. So, any decoders in the reversing segment are only exposed to a swap in polarity. There aren't any short circuits involved no matter how brief. I can't vouch for operating more than one train in the reversing segment when short circuit sensing is used to cause the polarity swap.
 
Markku said:
Thanks for the answers and comments. My initial feeling is that I may go mostly with LGB products as I have a local supplier in Helsinki. Other brands will require ordering from f.ex. Central Europe, so that always causes some unknown factors.

Phil, your last point about using only sensor mode if multiple reverse modules are present is interesting (in the literal meaning), I guess I have to remember that if I consider using two loops for some reason.

Also, the current limit is apparently something that needs to be considered...
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Hullo Markku,

I have 2 LGB 50080 Reversing Modules on my layout, on each line of a double tracked return loop. I can run a 6 car TTE train with power car each end as the loops are just about long enough.

I haven't yet had a train running in each loop at the same time, but I wouldn't expect any issues if I did....
 
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