I want to place an industry lead at the edge of a reverse loop. I am wondering what happens when you work out of and back into a reverse loop. I am using DCC, PSXAR's, & plan to have detectable wheelsets on all cars, or at least any trailing cars. Here is a scenario: Local Train A enters reverse loop with 5 cars. I'm setting out cars 2 & 3 to Industry X. (Industry X lead is at the edge of the reverse loop.) I cut away from cars 4 & 5, and leave them standing in the reverse loop. (These cars are equipped with detectable wheelsets, lighting, &/or a decoder.) I exit the reverse loop with engine and cars 1,2,3 and make my setout. I return to my standing cars in the reverse loop. What happens when I cross back into the reverse loop? Is the auto-reverser going to trip? Do I get a short? I've posted this diagram to help explain my question (red track indicates reversing section.) Thanks,
The auto-reverser will reverse the polarity whenever it detects a short. It may reverse when your train enters the reverse loop or when it exits it depending on what state it was left in. I don't see how your set-out and pickup scenario would give it a problem.
To make this simple, your AR will reverse if it has to, and only when a powered axle enters or leaves either end of the contiguous pink track that you show. For the industrial spur, it does not comprise a segment or branch of the reversing loop, so the AR will not be sensitive to it. In the direction of travel you show, the AR will only possibly engage once the diverging route is taken past the frog. If it doesn't engage there, it will when the same train completes the loop and enters the last turnout, assuming the loop is end-gapped just prior to that last frog. If the train proceeds past the points, it is still matched for polarity with the rest of the layout, and reversing into the industrial spur won't change that.
OK, so I think I get this. Reentering the reverse loop from the same direction I just exited will not cause a polarity shift. Polarities should already be matched, so reentry will not cause a short. So in the scenario I posted, exiting then reentering the straight leg of the loop will not cause a problem. I'm assuming then, that if I modified the scenario, and after I made the set out, I return to the standing cars 4&5 via the diverging leg of the reverse loop, that would cause a problem. I'm still a little confused about how an auto-reverser actually works. I'd like to explain what I'm assuming happens A train enters AR section by crossing gaps. AR module checks for same/opposite polarity If opposite, AR module flips polarity of AR track section If same, AR module maintains polarity of AR track section NOW IT GETS FUZZY FOR ME Train exits AR track section by crossing gaps AR module checks polarity for same/opposite If opposite, AR module flips polarity of AR track section If same, AR module maintains polarity of AR track section Does this sound right? Are the gaps the triggers? I was also concerned about the AR "rule": No more than one consist using an AR section at a time. Leaving cars in the section, then re-entering with the loco seemed to be a violation of the "rule". Thanks,
Like most 'rules' there is an element of simplification. The way ARs work is also somewhat misrepresented. Basically you must not bridge both ends of an AR section simultaneously (usually a loop, but could typically be a wye or turntable instead). AR operation. When you have out of phase polarity at the section end this is the situation: Rail A --------------||-------------- Rail B --------------||-------------- The two colours represent the different polarities, --||-- are the gaps. If something conductive bridges the gap in EITHER rail you have a direct connection between the opposite polarities - ie. a short. The heavy current that then flows is detected by the AR unit and it reverses the polarity (swaps the red/blue) of it's section to eliminate the short. Note that the short is between the rail ends (along the rails), not between rails A and B (across the track). The loco usually leads the train, so the common observation and assumption is that it operates the device, but this is not strictly correct. A powered or other current using vehicle is not required to create the short - just a conductive (metal) wheel, so for a steam loco it could be a pilot truck wheel that trips the AR over. At higher speeds a single wheel may not bridge the gap for long enough to trip the AR, in which case the lengthier connection provided by the longer, electrically connected wheelbase of a loco will do the job. This is also why the block should be longer than any train. Locos and lit cars typically have a number of wheels connected together for pick up, so they will bridge the gaps for some time. However even a non-lit trailing vehicle with metal wheels will bridge the entry gap momentarily as it passes which could cause havoc if the loco is already bridging the exit gap. There is no problem with leaving vehicles (powered or not) inside the section (but you need to make sure that they don't get added to a train that then becomes long enough to break the "block should be longer than any train" rule.)
Greg; You're making it harder than it is. When the auto-reverser detects a short between the primary rail power and the reversing section it reverses the reversing section to correct the short. That's all.
Mike explained it well, but the simple answer is, you don't have a problem. And with a loop like that, with the gaps right at the turnout, you are pretty well protected from bridging both gaps at the same time, since there would probably be a collision if oyu did that. So, just do it!
The old rule-of-thumb is... the length of the train cannot exceed the length of the reverse loop. And as jbos says, with both ends connected to the turnout you'd run into yourself if it did.
Thanks for Nothing Randall, I'm sorry for making this hard for you. I am not an idiot. I like to know how things operate, and determine the limitations before I devote time, money and energy to a project. I have read auto-reverser manuals, DCC books, DCC websites & model railroad forums, but I never saw this scenario discussed. That is why I asked the question. This issue has been on my mind for over a year, and it's getting close to time when I need to make a decision how I'm going to work in and around my reverse loops. If you had read my questions, you might have realized that I was trying to address the issue of cars left standing inside the reverse loop. That's why I took the time to come up with a scenario, draw a diagram and follow up with questions to help clarify what was happening. <sarcasm>Thank you for helping me</sarcasm>
All of the above comments are the thoughtful reasons as to why I selected photo-detection of a "stop-and-reverse-it" block, with control panel LED indication. Only current detection raises the problems. I'm DC. If I were DCC I would still do the same. Control panel LED's for hidden loops and landmarks for visible loops. The cars in the control block will be unaffected by, nor have any affect upon, the switching actions at the entry turnout to the loop. Another train in either of the the control blocks is another question. But how did the dispatcher let that happen?
