Saw this post and I want to know why. I will argue that a freight train can span both gaps in most cases.
Why can’t the train span both gaps in a reversing section?
Strictly speaking the train can span both gaps. But, it can’t have a wheel bridging a gap at each end of the section at the same time. If you have that situation, the autoreverser is going to have to try to match both ends at the same time, and you can’t get rid of the short. So, it’s much safer to not allow that be possible. As a note the problem can be caused by two different trains. If gaps at both ends of the section are bridged at the same time, you have trouble.
The basic theory is that if your train spans the second gap before it clears the first gap the auto-reversing circuit will get confused and switch back to the polarity of when the train first entered the reversing loop or section. This will continue until the train stalls or the AR (auto-reverse) has a melt down. If you plan ahead it is no problem to let your train completely clear the first gap before reaching the second gap. Most people change out the plastic wheels and axles for metal wheels and axles at some point. And with the metal wheels doing the shorting that trips the AR, if all the metal wheels are not past the first gap before the first metal wheel set reaches the second gap it will cause problems. An a $300 Investment in a good DCC control system along with the AR would be a hard pill to swallow to have to replace to whole shebang just for not setting up the AR and rail gaps right.
For cars manufactured in the past five years or so, all wheels on the trucks are insulated. All cars are insulated from each other except in rare cases.
Now if we were talking about a consist of locomotives or lighted passenger cars, I would agree with you.
But if the cars are not lighted and drawing current from the track, it still isn’t a problem.
Has nothing to do with insulated wheels. A metal wheel can momentarily tough the rails on either side of a gap in some situations. If it does that at the same time an engine or another metal wheels set bridges the gap, there’s a problem. On my last layout my ore trains were long enough that the engines could be leaving the reversing section while cars towards the end of the train were still entering it. I just made sure the last cars in the train were cars that had plastic wheelsets.
If you have a long train with plastic wheels there’s no problem, but if your cars have metal wheels there could be trouble. I have the same thing sometimes on my layout when a block won’t go off when I flip the switch off because a metal wheel is sitting right on the gap in the rails.
I have two short reverse sections of track that are in different locations on my home layout connected to one PS-REV module. All my rolling stock has metal wheels. I have no lighted passenger cars. I staggered the insulated rail joints approximately 1/8" at each end of each reverse section as recommended by Tony’s documentation that was enclosed with the PS-REV. I run trains through these sections of track, but not both at the same time, without any problems. As long as current-drawing locomotives or passenger cars are not crossing both ends of an insulated section, the PS-REV has no problem with this because rolling stock wheels alone don’t cause it to trip. The key here is to stagger your rail joints at both ends of the reverse section.
I believe the above to be in error. The auto-reverser works by sensing a polarity mismatch between the 2 sections of track, and changing the polarity of one very quickly to match. The actual sensing is caused by a short circuit that happens when any metal wheel bridges a gap between 2 rail sections of opposite polarity. Lighted passenger cars or locomotives have nothing to with it - it is a metal wheel spanning the gap that causes the action.
If you think this through carefully, you realize that staggering gaps merely insures that a given wheel set will not span 2 gaps of opposite polarity at the same time (or within milliseconds of each other), possibly causing confusion.
The bottom line is that any time you have trains rolling through both ends of a reversing section - can be 1 or 2 trains - you run the risk of auto-reverser confusion. If you can guarantee that you will never have metal wheels at the end of the too-long train, then you have a better memory than me. But why worry about the problem in the first place?
If you think about it, you can always make your reversing section just as long as a train can physically be w
Fred is right. There is a good chance that even if you violate the “rules” you’ll get a way with it, because getting a short at both ends is not really likely. A lighted car adds to the problem, because it extends the “trouble” zone from a fraction of a inch to multiple inches.
A rolling stock wheel will cause it to trip. It’s just that you are not likely to bridge both ends at the same time. With no train on the track, take a screwdriver, and bridge the gap on one rail, at he end that is mismatched. The PSX-AR will trip immediately. Staggering the gaps prevents the reverser from seeing the shorts on both rails close enough together to try to switch the polarity twice.
OK, I must admit that you have convinced me to make the reversing section longer than the longest train that will use it.
The kicker was that a single metal wheel will bridge the track gap causing the reverser to reverse, like using a screwdriver to bridge the gap as was mentioned.
OK, now let me throw out one more thing. If you made the gaps, or made an insulated section of rail (there are a couple of ways to do this) about one-half inch long, could your train span the reversing section without the problems previously described?
(I don’t necessarily want to do this, I’m just want to examine all the possibilities wheather it can be done or not.)
If you had lighted cars, you could still get into trouble. And if you used a short piece of rail, insulated at both ends you could get in trouble if different wheels (say at opposite ends of the same truck) bridged the two gaps at the same time. But, in general terms, you would decrease the problems.
One thing to consider is that the obvious place to put the reversing section is not always the only place it can go. Sometimes a less obvious place can be better.
A half-inch dead zone is going to mean that when an engine crosses it, there will be power to one less axle. Depending on the engine’s power pickup configuration, that could be a problem. For example, if you’ve got a 4-axle switcher with traction tires, then there are only 3 axles picking up power, and if you lose one to the dead zone, you’ve only got two. You may find this kind of engine will stall when passing over these dead zones.
If you’re running lighted passenger cars, the dead zone may cause them to flicker off and on.
For this to work as you want (train longer than the reversing section), the dead zone must be longer than the wheel span of your longest metal frame truck and none of your cars can have a metal underframe linking metal frame trucks. And pusher helpers would defeat this scheme.
The longest metal frame truck on a car would typically be a 6 wheel passenger truck. The dead zone would have to be at least that long. And there can be no low resistance path between the two trucks on the same side. A 4 wheeled bobber caboose with metal truck frame and wheel sets might be longer. In other words, you would need to check your car fleet, especially observation cars and caboose (since they would be at the end of a long train), to ensure they would not somehow electrically span the dead section. And as I said, no pusher locomotives at the end of the train.
The problem, as others have pointed out, is the longer the dead zone, the greater the likelihood of stalls.
Since you can, with a little effort, make the reversing section as long as any train that can physically be reversed, why fool with dead zones and the like? Just put the gaps right at th
FYI: Walthers passenger cars, even if they aren’t lighted, still pick up power on all axles. Each truck is connected to the other by the metal contact strips on the underframe. This means that if you have a passenger train made of Walthers cars that is longer than the reversing block, you are almost assured of having an auto-reverser short circuit.
IOW, for a 8-wheel freight car with metal wheels in plastic trucks, your contact area to be worried about is only one wheelset on the rail (a mere tiny fraction of an inch)
If that same car has metal trucks, that contact area is now the length of the truck wheelbase (perhaps 3/4").
If you have a Walthers 85’ passenger car, that contact area is now about 10" or so. Our club learned this lesson, and we used to have a reverse section only 11.5’ long. As a result, all Walthers passenger trains had to be less than that in length…or else it would short. Fortunately, that section of the layout was removed, and now our reverse section is some 30’ long.
Paul A. Cutler III
Weather Or No Go New Haven
Thanks for the information folks. It does all make sense.