DCC return loops questions

[Dan Griffin]

Hello.

 

I am currently building my layout and for my outdoor section I am planning on having it as a return loop, it will be about 60-70 foot in length and run to the garden shed (roughly half way along) and back.  inside the shed will be a couple of storage sidings and possible a mock coal mine. the line will be a preserved steam line. this shed will act as an intermediate signal box. splitting the loop into two separate signalling blocks.

 

the question I have is about running multiple trains with in the loop as it will be so long. will I be able to run two trains into the loop. both in the same direction, one behind the other, separated by the block post which will be the signals inside the shed. does a return loop module allow this to happen?

 

will having two trains inside the loop at the same time effect the return loop switching polarity of the rails?

 

I understand that all rails will need to be isolated with insulated fish plates and I understand how to wire the loop up.

 

this scenario is what is bothering me:-

 

train A runs into the loop, heads around and makes it ways back. once my son (signalman in the shed) has advised that train A is clear train B then enters the loop.

After train B has enetered and is clear of the insulated joint, the points are switch and the reverse loop module should change polarity of the rails. All well and good.

Train A then makes it back to the station from where is started. loco runs round and is ready to go back. Am I right in thinking that because the module has activated I will be unable to send train A back into the loop whilst Train B is still making it way back to the station?

 

I hope that makes sense. any help would be great.

 

 

[Nigelcliffe]

There is no problem with multiple trains in the reversing loop.   

The only potential problem arises if two trains can cross the boundary of any auto-reverser at the same time - then the auto-reverser cannot "know" which way to switch as its being shorted in both directions simultaneously.

 

With runs as long as you are describing, the bigger problem will be ensuring decent quality of DCC signal over the distances outside. 

 

If the loop is a simple arrangement - say a single turnout - then there is no real need for an "auto-reverser".  The reversing can be done by a pair of contacts on the turnout mechanism (eg. on the turnout motor, or a switch which also moves the tie bar), and set the polarity of the loop according to the setting of the turnout blades.  

 

 

 

 

[tender]

With a long reversing loop you don't have to isolate the whole loop, just a section before it rejoins the mainline that is slightly longer than the longest train.  Arrange your block signalling so there will then only ever be one train in the 'switched' part of the loop.

 

[John ks]

Adding to Nigelcliffe's post, I would be inclined to use a relay controlled by the point to set the polarity phase of the loop

John