Need a little help. I’ve got a reverse loop that in about 14 feet in total distance. It’s a DCC layout and I’m using a PSX-AR reversing unit. My question is how long should the reversing part of the loop be? I’m thinking at least longer than my longest engine configuration, but not necessarily as long as the whole loop. I can use part of the loop in a siding sitiuation and not trigger the reversing unit each time it’s used if I shorten the length of the reversing section.Appreciate any help.
The bounds of the loop that is PSX-AR controlled must be at least as long as the two most widely separated axles that permit power to cross the two rails. IOW, if only the locomotive(s) in question have power routing capabilities, then your loop only needs to be as long as the length of their consist. If you have powered heavyweights passenger cars, you’ll have to include them in length of the distance between the isolating gaps. And so on…
I use the PS-Rev, which is the forerunner of the PSX-AR. The instructions for it say that the reverse loop track needs to be as long as the longest train that you will run through it; however, this evidentally assumes that you will be running lighted passenger cars and/or a lighted caboose.
I have gotten by with much shorter reverse loop sections because I do not run any lighted passenger cars. One section is only 2 feet long, and I have had no problems with it not working correctly.
I have even fudged a little and connected two separate reverse sections to one PS-Rev because there’s absolutely no chance that a train will be in both at the same time.
I found that the recommendation to stagger the rail joints at the ends of the reverse loop was more critical than the length of the reversing section.
If I read you correctly, this means that a modeler running trains with detector resistors in all or a majority of his cars (and an operating FRED or lighted caboose) has to have a reverse section the full length of his train. Why? Lamps and detection resistors are not polarity or phase sensitive - or are they. The answer might affect my future decisions about DCC.
Chuck (modeling Central Japan in September, 1964 - analog DC, MZL system)
Think about a caboose with electrical pickups for lights, or whatever. If you reverse the polarity of the loop before the caboose has passed over the point where the polarity changes, then the caboose truck will present a short circuit while it has one axle over one polarity and another axle over the other polarity. So you have to get the entire train onto the loop before you switch polarity. Or, if the engine comes out the other end of the loop before the powered caboose enters the loop, you could switch the loop twice and make it all work OK.
There may be other solutions I haven’t thought about.
I may have to eat my words about the passenger cars. The link below suggests that it is only the lashup (can I still use that word with a straight face these days…dunno.) length that matters, not the passenger cars that are lighted. In any event, Chuck, you have seen this page in your travels, I am sure, but if not, perhaps it will help to assuage your anxiety?
The best option is to make your reverse loops such that there will never be more than one car on the loop’s boarders at any time. From here you can cheat, but the more you cheat, the more likely shorts will be.
I’ve carefully read the Loy’s Toys link. Thank you, Selector, for providing that. I think I agree with all of it.
It appears that the simplest method has a reversing loop longer than any train, if you are going to have electrically powered rolling stock anywhere in the train with no restrictions. This would include helpers.
It gets more complicated if you want trains longer than the reversing loop with no restrictions on electrical pickups.
If you don’t want to use the switch that Loy’s Toys sells, there is one more solution that I didn’t mention before. That would be to have a “block” on your main, the polarity of which you would reverse at the same time you reverse the polarity of the reversing loop. Make the length of this block long enough so that the total length of the reversing loop and the block together is longer than any train you will run. In effect, it gives you a longer reversing loop, electrically, without requiring the reversing loop track section to be be longer than the longest train.
After the last car or helper passes into the block, reverse the polarity of both the block and the reversing loop. Exit the loop normally, and restore the polarity of the block on the main after the last unit enters the loop.
Going in the other direction through the reversing loop, a train would enter the loop normally. You would make the polarity of the block match that of the loop and reverse polarity of both after the last unit enters the loop. When the last unit clears the loop, you would be free to make the loop ready for another move.
The bad news is that a short circuit will occur if another train comes along the main and enters the block before you restore the polarity of the block. Of course, it probably shouldn’t be that close, anyway.
One way to do this would be to use a turnout relay or switch machine contacts to change t