Wiring help needed

[Daveinnorfolk]

Hi everyone, 

 

Trying to work out how to solve this wiring problem. Attached is the track plan for my layout, operating on DCC. 

 

The blue rectangle is the 'main' layout, with the other section at the bottom a slightly later addition. At present, the track that runs A-C is powered, and A-B will accept the 'main' feed, though not yet fully wired. 

 

How do I solve the problem of B-C? Ideally I would like it that trains could traverse this section without stopping in the middle. I'm guessing some form of re-polarising is needed? 

I've seen several plans for wye junctions online but none seem to quite solve this problem so any help that can be offered is greatly appreciated. 

[Campaman]

You need a DCC automatic reversing unit which will change the polarity as it detects the difference. 

[Jeremy Cumberland]

This would be better posted in Modelling Zone > Power, Control & DCC > DCC Help & Questions

 

If you don't intend having a second train running on the bottom section at the same time as a train enters or leaves it, you could switch the polarity of the bottom section by using a DPDT switch that operates with points B. This is not as versatile as an auto-reverser, but it is simpler, and some people prefer it because it they understand how it works, rather than being some electronic trickery.

[ITG]

I currently use a Gaugemaster auto reverse module. Very easy and straightforward to wire. But on a new layout currently under construction, I will be using the Lodi auto-reverse module, simply because it does not draw any current - important for me as I am using current sensors for block detection.

You would be advised to ensure that the reversing section (B to C as you have it drawn) is isolated on both rails, and is also longer than your longest train. Train length may not be an issue if all stock wheels are plastic, but for example, if you have coaches or brake vans etc with lighting, you may be encountering shorts if the train length spans the isolation breaks.

ian

[Suzie]

6 hours ago, Daveinnorfolk said:

Hi everyone, 

 

Trying to work out how to solve this wiring problem. Attached is the track plan for my layout, operating on DCC. 

 

The blue rectangle is the 'main' layout, with the other section at the bottom a slightly later addition. At present, the track that runs A-C is powered, and A-B will accept the 'main' feed, though not yet fully wired. 

 

How do I solve the problem of B-C? Ideally I would like it that trains could traverse this section without stopping in the middle. I'm guessing some form of re-polarising is needed? 

I've seen several plans for wye junctions online but none seem to quite solve this problem so any help that can be offered is greatly appreciated. 

 

The trick to making this work is to power the whole section below 'B' as a reversing section. The simple answer will be to power it via an auto-reversing booster, but if you don't have too much on that section you could possibly use a simple electronic auto-reverser.

 

But, I would just use a double pole switch that works in conjunction with point B to change the polarity of the track below point B. Some motors have a double pole switch, like the Peco PL15.

 

Wire point B so that it has insulated joiners in the outer rails at the frog end, and you do not need isolated joiners on the frog (both frog rails are always at the same potential). As long as point B is set correctly you will be able to drive straight through.

[DCB]

13 hours ago, Campaman said:

You need a DCC automatic reversing unit which will change the polarity as it detects the difference. 

Where?  Logically you end up changing the polarity of the terminus,  much like Suzi's suggestion

[Jeremy Cumberland]

4 hours ago, DCB said:

Where?  Logically you end up changing the polarity of the terminus,  much like Suzi's suggestion

On the B to C side of the triangle. Or on the B to A side, but Dave said he intends wiring this up to match the main loop; also the B to C side looks to be longer.

[DCB]

Needs to be in DCC Modelling Zone > Power, Control & DCC > DCC Help & Questions.
None of the A-B,  B-C  or C-A  chords are long enough for a decent length train, so the guidance is OK if you don't run  trains with lights, more than 3 coaches long.  

[Enterprisingwestern]

 

Scroll to the bottom.

 

https://www.tamvalleydepot.com/support/frogjuicerinfo.html

 

Mike.

[Harlequin]

The OP needs to tells us how long those track sections actually are w.r.t. the longest train he expects to run through them. (And I agree, this topic should be moved to DCC Help & Questions.)

 

I would be unhappy to have an auto reverser in the main roundy-round circuit or completely switching the "polarity" of the bottom terminus, so I would do it this way:

 

Isolate the green tracks just before A and C, and at position D, and feed them from the Auto-Reverser. (Assuming that the green tracks are long enough to hold a complete train.)

 

[Jeremy Cumberland]

@Harlequin's approach has a different potential problem, though, in that you can't have two trains bridging different gaps simultaneously, which might affect how you want to operate the layout. I can imagine it being quite attractive to have one train departing via A at the same time as another train is arriving via C, for example. The second train will have to wait at points B till the first train has cleared, of course, but with the plan shown, the second train would have to wait at C, not B, and it would have to wait till the first train had cleared the isolated joint at A, not merely till the first train had cleared points B.

 

In the old days of DC, the first response to any question about how to wire a layout was usually to ask how the person intended operating the layout. This has largely gone away with DCC, and we no longer need to worry about where to place isolated sections or how to transfer control of a section from one controller to another, but it has not disappeared entirely.

 

Isolating immediately above points B and switching the whole bottom station makes it impossible for both gaps to be bridged simultaneously. Isolating the B to C side of the triangle makes it very unlikely that two trains will bridge the gaps simultaneously (unless you are aiming for a head-on collision), but it might be all-too-easy for one long train to bridge both gaps simultaneously. How long are your trains?

 

Then you have to consider the power demands of what you will be switching. Switching a short section of track on which there will only ever be one train is fine, and this is what auto-reversers are designed for. Switching an entire MPD full of locomotives, if that is what the bottom part of the layout is, might require a different approach.

[Daveinnorfolk]

Many thanks for the various responses given, and time taken to write them. Point about it being more appropriate in the other forum noted, and if any admin wants to move it then be my guest!

To answer the questions; 
A-B and B-C can both take around 3 coach lengths, which for the 'lower section station' is sufficient, as the looped platform can only take this. The 'lower section' is a separate station and yard area, rather than it being an MPD as Jeremy speculated. My main 'aim' is that trains can move across any of the three stretches of track to get to either the 'main' layout or lower station, or continue on the main layout, rather than multiple train movements needing to be controlled over this section of track in a short period of time. From your advice, it would seem that an auto reverser planted as per Harlequin's suggestion is the best move for my intended operation. 

 

Many thanks to everyone for your help.  

[St Enodoc]

5 hours ago, Daveinnorfolk said:

Many thanks for the various responses given, and time taken to write them. Point about it being more appropriate in the other forum noted, and if any admin wants to move it then be my guest!

To answer the questions; 
A-B and B-C can both take around 3 coach lengths, which for the 'lower section station' is sufficient, as the looped platform can only take this. The 'lower section' is a separate station and yard area, rather than it being an MPD as Jeremy speculated. My main 'aim' is that trains can move across any of the three stretches of track to get to either the 'main' layout or lower station, or continue on the main layout, rather than multiple train movements needing to be controlled over this section of track in a short period of time. From your advice, it would seem that an auto reverser planted as per Harlequin's suggestion is the best move for my intended operation. 

 

Many thanks to everyone for your help.  

Given this additional information, I'd support @Jeremy Cumberland's suggestion to treat the entire terminus and point B as a single power zone, switched either by an auto-reverser or by a mechanical switch on point B. I've done exactly this on my layout, using the two switches on a Cobalt iP Digital motor, as I have an inherent aversion to creating a deliberate short circuit, which is what an auto-reverser does. You don't need a third switch, because with this configuration the polarity of point B's frog is always the same.