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Return loop wiring query


Newbie2020
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I'm wiring my layout DCC as shown in the AnyRail plan. I've got the return loop working perfectly with a dual frog juicer working as an auto-reverser. My question is, do I need to isolate the central sidings between points 6 and 19? If I'm running a shunter in the sidings and a train goes through the reverse loop will the changing polarity affect the shunter?

 

If not, why not?

 

Confused.com

 

 

layout4.8 points numbered.JPG

Edited by Newbie2020
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I think that you could simplify things a little by only treating the upper half of the reversing loop as a reversing loop - i.e. only the section between point 6 and point 8. That means that the sidings off point 6 are always at the same polarity as point 5. I think that would make your concern about the sidings go away.

 

Would that work for you?

 

Mike.

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1 minute ago, KingEdwardII said:

I think that you could simplify things a little by only treating the upper half of the reversing loop as a reversing loop - i.e. only the section between point 6 and point 8. That means that the sidings off point 6 are always at the same polarity as point 5. I think that would make your concern about the sidings go away.

 

Would that work for you?

 

Mike.

OMG! That is so simple! I hadn't even thought of that!

 

Thankyou

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No need to make that change and it could give you problems with the reverse loop being too short. The shunter will not be affected, it just gets the polarity reversed under it the same as the train going through the reverse loop. The polarity reversal has no effect as the train direction is set by the throttle irrespective of polarity.

So its fine as you have it.

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Not sure exactly what caused it, but when I tried to run two locos simultaneously through my reverse loop in such quick succession that one was exiting the loop as the other one entered, I got a short. I use an auto-reverse module rather than two autofrog devices, but on that experience, you may have to be careful with a (second) loco passing over a point into the reverse loop zone, when a first loco is moving in the sidings.

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1 hour ago, ITG said:

Not sure exactly what caused it, but when I tried to run two locos simultaneously through my reverse loop in such quick succession that one was exiting the loop as the other one entered, I got a short. I use an auto-reverse module rather than two autofrog devices, but on that experience, you may have to be careful with a (second) loco passing over a point into the reverse loop zone, when a first loco is moving in the sidings.

 

You cannot bridge both ends of a reverse section at the same time, otherwise there will be a polarity conflict.

The advice is to always make sure that your reversing section is longer than your longest train.

 

By running  two trains across both ends - the loop module will "see" them as one.

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10 hours ago, Grovenor said:

But the loco in the sidings is not near the reversing section boundary so will not be an issue.

 No, but by having the reversing section so short between points 6 & 8, surely that severely limits train length, as quoted by newbryford@.

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3 minutes ago, RobinofLoxley said:

I think the train length only affects any part of the train that draws current/is detectable. So its only the loco unless you have carriages fitted with resistors for example so they can be detected

 

Absolutely correct, but as one of the benefits of DCC is continual track power, there are increasing amounts of stock fitted with lighting and/or tail lights.

So the safe option is not to use trains that are too long.

 

 

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5 minutes ago, RobinofLoxley said:

I think the train length only affects any part of the train that draws current/is detectable. So its only the loco unless you have carriages fitted with resistors for example so they can be detected

If you have metal wheels on the train then they will also cause a polarity conflict if a wheel bridges the gap at the same time as the loco crosses at the other end.

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Not an electrical point, but do you mind if I make a couple of comments on the track plan? (assuming the track isn't finally laid and ballasted yet!)

 

In many ways it's a very nice track plan - a train can start off from the terminus, go round the main line and get back again (a lot of plans seem to feed a terminus on to an oval without any way of getting back). Good to have a couple of carriage sidings at the top - always useful!

 

However the arrangement of crossovers on the oval is somewhat awkward as it means a train has to do about half a circuit 'wrong line' to reach the reversing loop, and another half a circuit wrong line to cross from the inner loop back to the terminus.

 

Could I suggest you would be better removing points 7 and 10, moving point 8 to the outer loop opposite where 7 was, and putting a diamond crossing where 8 used to be, so that a train can cross directly from the outer loop to the reversing loop. Also moving points 9 and 10 to adjacent to the tunnel mouth will enable a train to cross from the inner loop to the terminus more easily (as a bonus 12 and 13 could then be moved one track section to the left, lengthening the second siding).

 

Points 1,2,3 and 4 as far as I can tell would then be superfluous.

 

 

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1 hour ago, RobinofLoxley said:

So the best answer to the original question is that since activities inside the loop aren't affected by it, leave the loop with the longest track section available which is from the points 5 to 8.

 

Agreed.  The purpose of the auto reverser is to ensure that you have the same polarity arrangement either side of the section break as the train enters the section (eg at 5) and then the auto reverser switches so that you have the same situation when the train leaves the section (eg at 8).  What needs to be avoided is something on or spanning the section joints at each end simultaneously (ie something that spans the isolation gap at 5 and something else that spans the isolation gap at 8).  This will create a short.

 

Where a train has lighting or resistor wheel sets for automatic train detection, then it's obvious that the maximum train length should be shorter than the length of the auto reversing section.  However, as @WIMorrison points out, it would be possible for the leading locomotive to straddle the isolation gap at 8 and for any wheelset passing over the isolation gap at 5 to cause a momentary short.  This therefore means that unless your rolling stock has plastic wheels then train lengths should be restricted to the length of the auto reversing section even if you don't have lighting or resistor wheelsets.

 

The moment of trains in and out of the sidings in this section (which is what prompted the original question) shouldn't be a problem, as the train using the sidings will never span the isolation gaps at both 5 and 8 simultaneously.  As such, there shouldn't be a need to isolate the sidings.

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17 minutes ago, RJS1977 said:

Could I suggest you would be better removing points 7 and 10, moving point 8 to the outer loop opposite where 7 was, and putting a diamond crossing where 8 used to be, so that a train can cross directly from the outer loop to the reversing loop. Also moving points 9 and 10 to adjacent to the tunnel mouth will enable a train to cross from the inner loop to the terminus more easily (as a bonus 12 and 13 could then be moved one track section to the left, lengthening the second siding).

 

Points 1,2,3 and 4 as far as I can tell would then be superfluous.

 

I agree with all of these suggestions.  I'm assuming that the purpose of points 1, 2, 3 and 4 is to allow trains to terminate at the lower station, for a locomotive to run round and then for the train to leave in the opposite direction.  However, if that was the intention, it would be better if both were trailing crossings to remove the need for wrong line running on the inner line in the clockwise direction.

 

I suspect that the arrangement was chosen to allow access to the return loop, so an arrangement with two trailing crossovers would require the diamond crossing arrangement you suggest at 8.

Edited by Dungrange
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I think there is a problem having the sidings off point 6 and also trying to treat the whole of the section from point 5 to point 8 as the reversing loop. 

 

Let's assume that a train is making some movement between point 5 and the sidings. Now see what can happen if a second train is permitted to travel on the track from point 8 towards point 6 (I'm assuming that it gets stopped short of point 6 by a signal, say). In this case, the first train needs the polarity one way, while the second one needs the polarity set the opposite way - a clear conflict.

 

I can agree that the reversing loop section must be capable of holding the maximum length train. If the section from point 8 to point 6 is treated as the reversing loop, to avoid the conflict, one approach that retains the sidings might be to shift point 6 nearer to point 5 - e.g. flip from using a LH point to a RH point - making the section from point 8 to point 6 longer.

 

Another approach is to prevent separate train movements between 8 and 6 and 5 and 6 - e.g.interlock points 8 & 6.

 

Yours, Mike.

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The trouble with moving 6 towards 5 is that it makes it more likely that shunting moves would impinge on the main line (so you couldn't have a train going round the inner loop while shunting is going on.

 

I don't think it's likely that a train would be brought on to the section between 6 and 8 while a move into the sidings is going on - assuming the layout is only going to be worked by one operator, he wouldn't be able to control both movements at once (even if he had two handsets, it would be a task of quite mental and physical dexterity!)

 

The better solution would be the second one - namely to wire the motors on 7 and 6 together as a crossover so a train can't accidentally be diverted onto the oval while shunting is going on.

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Thanks everyone for the contributions - I've learned a lot! I'll look at the changes in layout too (track is only pinned down so far!).

 

I have put the sidings in now and tested it and the shunter is not affected as a train goes through the return loop!

 

Cheers

 

Clive

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On 19/12/2020 at 20:41, RJS1977 said:

Could I suggest you would be better removing points 7 and 10, moving point 8 to the outer loop opposite where 7 was, and putting a diamond crossing where 8 used to be, so that a train can cross directly from the outer loop to the reversing loop.

I have changed the plan to reflect  RSJ's suggestion

 

I have also altered the access to the terminus with a crossing X1

 

By moving 11,12,13,9 & X1 to the right you get a much smoother access to the terminus   but you lose most of the siding from 12 to its end & getting settrack points of the correct geometry might be difficult 

 

Regarding the reverse loop 

If you require the RL section to be longer than from 5 to 8

You could extend the loop to point 1 

It would require a relay controlled by point 8 or a switch mechanically linked to point8 that switches the feed to the section between the orange dots (point 8 to 1) from the main bus to the reverse loop. in this case you could reduce the reverse loop section to the section between  6 & 8 (Red & orange dots. Dots represent IRJ's in both rails)

 

 

1116288211_layoutrloop.png.81d619ca14f3f39e1a2318a04fac9916.png

Some more food for thought

John

 

 

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Referring to the above, if you replace the crossing between points 11 and 9 with a single or double slip you would appear to be able to do away with almost everything to the right of the slip. But that wouldnt personally have been my starting point if I was asked how to improve what is basically a good track plan.

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