Planning for a reverse loop in DCC

[GordonBigBoy]

Greetings from Thailand. Complete beginner here having only ever owned a trainset by Lego before!

I have just picked this up from the platelayer website http://www.freewebs.com/platelayer/tipsandwiringdiagrams.htm where they discuss reverse loops:

 

For

 

DCC users there are automatic reverse loop controllers available. These require no intervention by the user other than changing the point. There is no need to stop the train. The auto reverser takes care of switching the polarity. In use, you will probably

 

not notice any slowing or jerkiness of the train.

 

My layout will be controlled by a Hornby 'select' controller with a 4 amp supply. I am planning for the points to be DCC controlled using the separate decoder and motor (hope I got that right?) Has

 

anybody got experience of the automatic reverse loop controllers mentioned above. Any tips on connection and a part number/supplier would be appreciated.

[Fishmanoz]

Hi Gordon BB, me again - you are certainly learning well and have it right above concerning reversing loops and using reversing loop modules, and about point motors and decoders.

You can actually avoid the use of a reversing loop module but only if

 

you use live frog points with integral polarity switches in your point motors that can be wired to reverse the polarity in the loop when the point is thrown. BUT, you have to stop the loco while you throw the point and reverse the polarity. Two point motors

 

that do this are tortoise and cobalt. Again, Brian Lambert has info at http://www.brian-lambert.co.uk/Electrical-2.htm#Reversing Loops. You might check first on his live frog point switching info, or on this site where the diagrams are colour-coded for ease

 

of understanding http://www.wiringfordcc.com/switches.htm

[Flashbang]

Hi

These thing should be observed for a reverse loop to work correctly..

1) Four insulated rail joiners (IRJs) are fitted to the beginning and end of the loop. They are fitted into each rail of the loop and the pair are directly opposite each other.

2)

 

The distance between the two pairs of IRJs should always be longer than the longest train (loco plus carriage or wagons) ever likely to travel around the loop i.e.the whole of the train MUST be inside the four IRJs.

3) Using a reverse loop module is probably

 

the easiest to do. It has four connections - two from the input side of the loops rails or DCC bus pair if you use a DCC bus. The other two which are the Output pair of terminals connect to the rails of the loop somewhere between the four IRJs.

4) No other

 

electrical feeds must be connected to the loops rails.

 

Reverse loop module produced by Hornby for use with the Select or the Elite is part number R8238.

[GordonBigBoy]

Thanks for the advice, I think I need to practice with this and learn by trial and error as it seems far more advanced than Lego! Joking aside, I have now had a look at the Hornby R8238 (albeit online) and will probably use one of these to deal with a

 

reverse loop if my layout needs one - hopefully it won't - see next thread. Thanks again for the valuable info.

[SteveWillis]

Could I ask why the whole of the train must be in the loop, given that there is no electrical connection between the locomotive and the coaches?

 

I ask because I am planning a new out and back layout that will have a section less than 24 inches

 

where polarity will need to be reversed, and while that is long enough for all my oo locos, it obviously is not long enough for the whole train.

[Flashbang]

The reason is that the whole train has to be inside the loops IRJs is simply any metal wheel rim will bridge the IRJs and cause the 'Trip' to occur and allow the RLM to flip its output.

So for example, if the loops length is shorter that the longest

 

train then as the train exits the loop its b=very first metal wheel will short the IRJs and 'tell' the RLM to swap over the loops rail power to match that of the exit rails power.

But if the whole train hasn't entered the loop as soon as any metal wheel

 

crosses the entrance IRJs the the RLM will be instructed to flip the rail power back to that matching the input tracks. Then the exit IRJs are bridged by the train leaving and again the RLM is required to set the loops power to match the exit. Eventually the

 

entrance and exit IRJs are likely to be bridged at the same time - Result then is total shut down of the main console rather than the RLM being able to flip the loops rail polarity seamlessly.

[Flashbang]

Sorry....I wish this forum had either a 'pre view post' or better an 'Edit post' option and then we could correct typing errors! But it doesn't, and there are several errors in the above post. So it should read.....

 

The reason is that the whole

 

train has to be inside the loops IRJs is simply any metal wheel rim will bridge the IRJs and cause the 'short circuit trip' to occur and allow the RLM to flip its output.

So for example, if the loops length is shorter that the longest train then as the

 

train exits the loop its very first metal wheel will short the IRJs and 'tell' the RLM to swap over the loops rail power to match that of the exit rails power.

But if the whole train hasn't entered the loop? As soon as any metal wheel crosses the entrance

 

IRJs the the RLM will be instructed to flip the rail power back to that matching the input tracks. Then WHEN the exit IRJs are bridged by the train leaving again the RLM is required to set the loops power to match the exit. Eventually the entrance and exit

 

IRJs are likely to be bridged at the same time - Result IS then a total shut down of the main console, rather than the RLM being able to flip the loops rail polarity seamlessly.

[GordonBigBoy]

There is an excellent diagram of how to set up the Hornby R8238 reverse loop module on the pdf doc in Hornby Downloads https://www.hornby.com/filelibrary/download/?FileID=176

I am guessing you need to buy extra the 2x isolating tracks R618 separately

 

or are they included with the module in the box?

[Flashbang]

Isolating tracks are not included.

You will need two and ensure you unplug and remove the short bridging link wires from each section.

 

You don't have to use R618 isolating track sections at all. Simply remove the metal rail joiners on the rail

 

ends where the loop starts and ends (Four metal joiners removed) and fit in their place four insulated joiners - R920 or the 'other firms' SL11 ones. This is a much cheaper option than using the isolating track sections and IMO looks far better too.

[GordonBigBoy]

Flashbang said:

You don't have to use R618 isolating track sections at all. Simply remove the metal rail joiners on the rail ends where the loop starts and ends (Four metal joiners removed) and fit in their place four insulated joiners

Thanks

for the tip - very useful.

[Christopher-1214885]

Hi All trust you are well. My challenge at the moment is that Hornby have discontinued the R8238 RLM and the Gaugemaster DCC40 requires you to switch off the Railcom in order for you to use there unit. Are therev any other suppliers compatible with the Hornby Elite?

Mod note - the question about alternative RLM devices is covered in the RLM guide often referred to on the forum.

The DCC40 instructions here make no mention of Railcom.

https://www.gaugemasterretail.com/magento/media/downloads/dcc40.pdf

[Brew Man]

Block Signalling make an excellent Reverse Loop Module for under £30, (at least it was when I bought mine last year).

[Chrissaf]

At the top of the "DCC Forum" is a sticky thread for a "Reverse Loop Tutorial" near the end of the document there is a list of R8238 alternative products that were available at the time of the document publication. I use TamValley RLMs with my Elite, but I don't use Railcom so cannot comment on that aspect.

[T Cat]

Hi iam planning on extending making my goods yard a bit more interesting which will involve a reverse loop. Just after a bit of advice as iam not sure where i should put the track isolotors. Ive hopefully attached a quick sketch of the proposed layout and will need a RLM.

Could i put the isolators as marked in red and just switch that sectio or would this cause an issue? Or do i put the isolators marked in Green which would isolate the entire section.

Many thanks

[T Cat]

[Chrissaf]

I haven't analysed the green option in great depth, but my initial assessment is that using the green locations will not work. The red locations are more typically used in what is in effect a WYE reverse loop. But I have one caveat, the physical distance between the red locations needs to be further apart than the length of your longest train [train = loco plus rolling stock].

Read my downloadable Reverse Loop Tutorial from the sticky thread and read the section on WYEs.

Note that the red location shown on the point on the main loop, needs to be on the WYE side of the point and not the loop side of the point.

If the red section is too short for your longest train, then relocate the lower right green to the centre left to become a mirror image of the red in the centre right and use that longer green section as the RLM protected track length instead of the red shorter red track section.

[Chrissaf]

T Cat,

You will have more success replying if you use the Reply Text Box at the bottom of the page and ignore the within post blue button, which is not a 'reply to this post' button. Your last reply attempt (removed) just duplicated my earlier reply and did not add any new text.