I am contemplating having a reverse loop on my DCC layout, I understand the auto reverser has to be specific to DCC.
Two questions:
Is there any difference between brands of auto reverser as far as quality, reliability, ease of installation etc?
The isolated section of track that the auto reverser is wired to has to be longer than the longest train that I intend to run due to metal wheels bridging the rail gaps / isolating track joiners. So the entire train is on the isolated section when the polarity reverses.
Do I have that right?
Any other advice or comments are appreciated.
Thanks.
Some auto reversers are solid state digital like the PSX-AR. I recommend that one. Other auto reversers, like the Digitrax AR-1 have a manual relay which reacts slower than a solid state digital auto reverser like the PSX-AR. Another solid state auto-reverser is the NCE AR10. Most auto-reversers are compatible with different DCC systems.
As soon as the lead loco enters the reversing section, the polarity flips inside the reversing section to match the polarity of the non-reversing section that the train is leaving. As soon as the lead loco exits the reversing section, the polarity flips inside the reversing section to match the polarity of the non-reversing section that the train is entering.
I think you understand the concept, but that is not the way to state it, because the train can enter the loop and the polarity might need to be changed, but most of the train is still outside the isolated section. The first wheels trigger the reversal and all the wheel sets after that are fat and happy.
The polarity should not change again (if the isolated section is too short, it would) until the rest of the train is in the isolated section.
As to your first point, some reversers do not play nice with some of the faster circuit breakers. The CB on the non isolated section detects a short and shuts down before the reverser does it’s thing.
If the polarity inside the reversing section does not match the polarity of the non-reversing section that the train is leaving, the polarity inside the reversing section will flip immediately to match the polarity of the non-reversing section.
Once the entire train is inside the reversing section, the polarity inside the reversing section will not change until the lead loco begins to exit the reversing section.
If the polarity of the non-reversing section that the train is entering does not match the polarity inside the reversing section, then the polarity inside the reversing section will flip to match the polarity of the non-reversing section that the train is entering.
I hate to jump into auto-reverser discussions, because I always seem to add more confusion. But I don’t think the OP’s second question has been answered yet.
A reversing section (RS) has two gaps, one at each end.
When a loco enters a RS and the polarity of the section it is leaving matches the polarity of the RS, nothing happens. If the polarities don’t match, the metal wheels of the loco causes a short and the AR responds by switching the polarity of the RS to match the polarity of the section the train came from.
While the train is completely within the RS, the metal wheels of the trailing cars have no effect while crossing the rear gap.
When the loco reaches the gap up ahead and the polarity of the next section matches, then nothing happens. If the polarity of the next section doesn’t match, then the metal wheels of the loco causes a short and the polarity of the RS switches and the RS no longer matches the previous section behind. Any metal wheels still behind the first gap will cause a short and provoke a reaction from the AR.
Moral of the story: RS track length must be longer than the train. Or, use plastic wheels on all rear dragging rolling stock.
Thanks everyone, it makes sense how, when, and why the auto reverser changes the polarity, my thinking was off some what.
As to why I need to do this. Currently I do not need an auto reverser but I am considering a change to my track plan and I know it will create a reverse loop. I am planning ahead so the reversing section is gapped properly and large enough.
I appreciate the info about the solid state digital vs the manual relay AR. Thanks.
But even if you’re careful and make sure all trains are shorter than the reversing section, there is one other thing to think about.
Two trains going whatever direction cannot cross both gaps at the same time or a short and a shutdown will result. Usually not a problem for a single operator. But sometimes there might be another operator who has a tendency to tailgate or who doesn’t look ahead to see if the RS is already occupied . . .
Can I ask how an auto reverser works in the case of a wye? In particular, where would the gaps be in this example? Some trains will be longer than the legs of the wye. How will this work?
It works the exact same way. The easiest thing for a wye is to isolate the tail and connect the AR there. If you pay attention when wiring the feeders, the main side plus one leg will have the same polarity all the time. Only the second leg will need the feeders reversed to match the main. So if you isolate the tail section, that is the only place where a mismatch will occure, when coming in from one leg and leaving via the other.
However, with the yard and all the complicated track across the top - it might be easier to isolat the lower leg, the one that is just a simple curved piece of track from the turnout int he yard to the turnout int he main. The top leg, adn the entire yard, would match the main so there would be no conflicts through there. But that means that lower leg needs to be long enough to handle the longest train. It looks like it is longer than the track in the yard after the turnout - you can compute the length in 3rd PlanIt and verify that, which would make it virtually impossible to bring a train through there longer than the leg of the wye - it wouldn;t clear the turnout into the yard
You could also isolate the entire yard by gapping #11 and #A (or the point to the right of #A just off the edge of the image). But I don’t know if the circuitry of your AR can carry the load of a bunch of engines in the yard.
My situation is similar, and I use a Digitrax booster configured as an auto-reverser. I don’t know the details of your power and control systems.
My balloon track is 13’ long and if I cut out behind the baggage cars I can turn a passenger train. The balloon track is closest to the RH and has the PSX-Ar and it has worked flawlessly for years. The gaps are right at the turnouts on either end.
First, thanks to you and Randy for your responses.
I haven’t purchased an auto reverser yet so my choices are wide open. I am currently using an NCE Power Cab but I will upgrade to an NCE 5 amp wireless system once the layout is operational.
I’ll have to spend more time studying the issue. I’m a bit slow when it comes to figuring these things out.
Dave, I applaud your choice of DCC power by moving up to the NCE PH-Pro 5 amp wireless system. You can keep your NCE Power Cab as well to support the PH-Pro. When you purchase an auto reverser, I recommend the PSX-AR which can easily support the engines in your yard.
I can’t recommend the DCC Specialties PSX-AR enough. I have 12 of them on my layout that cover 2 levels, a turntable and WYE. They work flawlessly and very happy with them.
NCE has an all electronic one now as well. Though for whatever reason, it is priced higher than a PSX-AR. For breakers I’d just as soon use the EB-1 from NCE, they are solid state like the PSX and have 99% of the features for a lower cost.
Though on several layouts I’ve helped with there has never been a problem with the much simpler Digitrax AR-1. Relays do not equal bad. And I never had a problem with my PM-42, either. Even deliberately attempting to cause problems by putting all my sound locos int he same section and shorting it. I know people have said they had problems with it not resetting with just ONE sound loco - to that I say, check your wiring. Because I had at the time 5 sound locos plus a couple of non-sound sitting in one section of the breaker, I shorted the track, the power cut out as expected, but only the one section of the breaker, other track had power, when I removed the short, all my sound locos started up again. No inrush problem. However, a PM-42 is really only usable for Digitrax layouts because that is the only way to configure the trip current.
The AR-1 has been sort of replaced with the BXPA1, which is both an autoreverser, a breaker, and a track detector - all soild state, no relays. Trip amps and trip speed easily set with potentiometers.
One thing I like about the AR-1 is that there’s a pot to adjust the sensitivity of the detection circuit. Over the years several people have put up posts about their autoreverser not working, and it turned out it was because they bought one that wasn’t adjustable. When they replaced it with the AR-1, their reverse loop worked fine.
