I have read a few posts on reverse loops and I understand that ideally your reverse loop should be longer than your longest train. I plan on having a long reverse loop on my layout which could accomadate more than one train. I’m new to DCC reverse loops and was wondering if having a second train entering the loop, while the first train is still in the loop, causes a problem or short. If not, does it cause a problem or short for the second train when the first train leaves the loop. I plan on using one of the DCC auto reverse loop devices like the MRC, I also plan on using atlas code 83 turnouts to enter the loop (not sure if this matters).
It’s kind of old tech, but I still use an Atlas twin. That way I can cut power off to the section when I want very easily which has a lot of benefits such as those concerning your question–not that they aren’t automatically addressed. I’ve got a PSX AR still uninstalled–not because it won’t work, I just personally like the manual approach with simple ability to turn off. Also, since we use a lot of sound locos as well as a few without DCC decoders it helps. Locos without decoders shouldn’t sit idle on a DCC track for long, motor just oscillates.
The turnouts do not affect the operation of the reverse loop - they have to be wired correctly regardless. Atlas turnouts need no special wiring as long as you are content with the unpowered frogs.
The electrically isolated reversing section should be longer than your longest train you will reverse. You can operate longer trains elsewhere on the layout, but you may have problems when you send them through the reversing section.
The autoreverser works by sensing a short circuit when the metal wheels of the train span one of the isolation gaps for the reversing section, and the reversing section is of the opposite polarity as the next/previous section of track. Because of how the autoreverser works, a train that is longer than the reversing section can be spanning a gap at both ends of the reversing section simultaneously. The auto-reverser gets confused when this happens.
The same autoreverser confusion happens if 2 separate trains are spanning gaps at both ends of the reversing section at the same time. Or you leave cars or locomotives with metal wheels standing on the reversing section gaps.
You have to set up your operation to avoid spanning gaps at both ends of the reversing s
I thought that the second train entering the reverse loop while the first train was still in the loop could cause a short, but I wasn’t sure. You confirmed this. I never thought about making my reversing section shorter than the entire loop, but your idea of doing this should help minimize the chances for a problem. It sounds like the rule of thimb is make your reversing section at least as long as your longest train, but not too much longer than the longest train.
I may add a signaling device to the layout before the reversing loop gap so I can halt the second train at that point, and have it look somewhat prototypical.
If it really is a reversing loop, as opposed to a reversing section, then you have no problem. A typical reversing loop starts right after the frog end of a turnout, goes around in almost a complete circle, and then joins up with the other frog-end track of the same turnout. In this case, it’s not physically possible to bridge both ends of the loop at the same time.
What you have to watch for, though, is a section of track that reverses a train, but where the gaps are not close enough to preclude spanning both of them. If you consider an oval with a diagonal track going across, this is the sort of arrangement which could lead to this issue.
It’s all about the gaps, and making sure you never span both of them at the same time.
I’m a big fan of auto-reversers, particularly the better ones like the PSX-AR. These are solid-state, not relay based, and they will generally flip the polarity faster than a relay unit. A relay is probably still fast enough for most purposes, but sound engines in particular sometimes will recycle the sound and even go through an engine startup cycle if power is interrupted for too long.
What you have to watch for, though, is a section of track that reverses a train, but where the gaps are not close enough to preclude spanning both of them. If you consider an oval with a diagonal track going across, this is the sort of arrangement which could lead to this issue.
It’s all about the gaps, and making sure you never span both of them at the same time.
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That’s like one of the reversing sections of the layout where we have the Atlas Twins. There are actually two diagonals plus other sidings, etc. generating in effect 4 reversing sections.
Thanks Mister Beasley. I think I have a reversing loop and not a reversing section. I have two parallel tracks which diverge and create a connecting loop which visually looks like the outline of a lightbulb. At the base of the “bulb”, I plan to have a turnout between the two parallel tracks which will allow me to either continue out the other side (not a reversing action) or reenter the track which started the loop, but I’m now going in a different direction. I believe it will only create a reversing loop when the turnout is switched to send the train back on the same track it originally came from. It’s hard tp explain without a drawimng and I haven’t figured out how to attach a pdf. etc., yet.
Every reversing loop is a reversing section, but not every reversing section is a reversing loop.
If I understand your description, you have a reversing section because the track does not completely fold back onto itself.
When you say that you have a turnout between the two parallel tracks, do you mean a pair of turnouts that create a crossover? If so, you will need to isolate the reversing section by placing gaps between the two turnouts and also on the two parallel tracks. In other words, you need three sets of rail gaps to completely isolate the reversing section.
The diagram on the top shows the reverse polarity and the gaps necessary to avoid a short. The bottom diagram shows the resulting matched polarities between the turnouts forming the crossover by placing gaps where the two turnouts meet. The remaining gaps are necessary to completely isolate the reversing section from the rest of the layout
