Reversing Loop Problem

Model Railroader Electronics and DCC
1

I need help. I am working on a midsized ho layout. It has 2 reversing loops that are at either end of a section of track. I am using Atlas Switch Machines on each of the Atlas turnouts at the entrance to each reversing loop. I am using a an NCE Power Cab DCC Starter Set. There is one Power Block that is divided into 3 power districts - one for each of the reversing loops and one for the connecting track.

Each reversing loop has a DCC Specialties’ PSX-ARSC circuit board that provides circuit protection, polarity reversing and turnout switching. You can go into each loop 2 ways and come out 2 ways - depending on how the turnout is switched. I am not having any problem with one of the loops.

The loop that is having a problem never causes a problem when the train is entering it - no matter which way the turnout is configured. When the train is exiting the loop and the turnout is switched, there is no problem. When the train is exiting the loop and the turnout is not switched there is a problem. The locomotive exits the loop, the polarity is reversed and when the train reaches the frog it stops for a short time and then proceeds. If I stop the train after it has crossed the track insulators and before it hits the frog and then start it it continues without a problem.

Any ideas out there? I am not very experienced and I have no idea what is happening. I have tested the voltage on the track in all areas around the exit to the reversing loop and the turnout. The voltage and current are constant. I am using a DCC Specialties’ RRAmpmeter III to test the voltage and current.

Please tell me this is not a poltergeist.

2

Hi Brendan:

Please let me restate the problem you are experiencing in my own words so I can be clear about what is going on.

In other words, if the train is exiting the reverse loop via the ‘through’ route (or straight route) that is when the problem is occurring. Correct? (I’m sure everybody else understands what you are saying but I am having a bit of a senior’s moment).

How far are the rail insulators on the loop side of the straight through route from the frog? In other words, is the back of the locomotive completely clear of the rail insulators before the front of the locomotive reaches the frog?

Dunno if that has any relevance, but I’m trying!

Dave

3

Hey Dave, you understand the problem. I don’t exactly know how far the rail insulators are, but I will measure it. I don’t think that would matter because once the polarity reverses, the entire loop and the non-looped section the train is moving onto are at the same polarity.

The loops polarity reverses as soon as the locomotive’s fron

4

Let’s try to add some precision to this issue.

Based upon all of the pertinent information in your other thread, you have a reverse loop at either end of your mainline. The mainline is protected by a PSX-1 circuit breaker, each reverse loop is controlled and protected by a PSX-ARSC.

You operate an NCE Power Cab, and your turnouts are Atlas Snap Switches. You indicate that one reverse loop operates flawlessly, regardless of the direction of the entry/exit of the loco. But, on the other reverse loop, the loco only operates without pause when the loco enters on the straight through route or when it enters or exits on the divergent route. So, you say that the only time the pause occurs in when the loco exits the reverse loop on the straight through route.

When the loco exits the troublesome reverse loop on the straight through route, it pauses at the gaps, then proceeds. Is it a short or is it a stall? To my way of thinking, it is a short, a momentary short, not a dead short, because it starts up again on its own without any assistance.

It could be the result of a lot of things: faulty wiring, incorrect or insufficient placement of gaps, PSX settings, the turnout itself, the loco. My educated guess is that there is a conflict between the circuit breakers. You have four circuit breakers on your layout: two PSX-ARSC’s, a PSX-1, and the booster itself.

What I believe is happening is that the short that the PSX-ARSC has detected is not corrected in the milisecond that it takes to flip polarities before the PSX-1 senses the same short and trips the current. When the system resets itself, the loco continues.

That is just a guess, but an educated guess, because we have dealt with this kind of issue before on the forum.

If it were me, the first thing I would do is to swap the turnouts that control both reverse loops to determine if the turnout is the culprit. That would narrow down the search for the cause of the problem.

Rich

5

[quote user=“richhotrain”]

Let’s try to add some precision to this issue.

Based upon all of the pertinent information in your other thread, you have a reverse loop at either end of your mainline. The mainline is protected by a PSX-1 circuit breaker, each reverse loop is controlled and protected by a PSX-ARSC.

You operate an NCE Power Cab, and your turnouts are Atlas Snap Switches. You indicate that one reverse loop operates flawlessly, regardless of the direction of the entry/exit of the loco. But, on the other reverse loop, the loco only operates without pause when the loco enters on the straight through route or when it enters or exits on the divergent route. So, you say that the only time the pause occurs in when the loco exits the reverse loop on the straight through route.

When the loco exits the troublesome reverse loop on the straight through route, it pauses at the gaps, then proceeds. Is it a short or is it a stall? To my way of thinking, it is a short, a momentary short, not a dead short, because it starts up again on its own without any assistance.

It could be the result of a lot of things: faulty wiring, incorrect or insufficient placement of gaps, PSX settings, the turnout itself, the loco. My educated guess is that there is a conflict between the circuit breakers. You have four circuit breakers on your layout: two PSX-ARSC’s, a PSX-1, and the booster itself.

What I believe is happening is that the short that the PSX-ARSC has detected is not corrected in the milisecond that it takes to flip polarities before the PSX-1 senses the same short and trips the current. When the system resets itself, the

6

[quote user=“Brendan Buschi”]

richhotrain
When the loco exits the troublesome reverse loop on the straight through route, it pauses at the gaps, then proceeds. Is it a short or is it a stall? To my way of thinking, it is a short, a momentary short, not a dead short, because it starts up again on its own without any assistance.

richhotrain

Let’s try to add some precision to this issue.

Based upon all of the pertinent information in your other thread, you have a reverse loop at either end of your mainline. The mainline is protected by a PSX-1 circuit breaker, each reverse loop is controlled and protected by a PSX-ARSC.

You operate an NCE Power Cab, and your turnouts are Atlas Snap Switches. You indicate that one reverse loop operates flawlessly, regardless of the direction of the entry/exit of the loco. But, on the other reverse loop, the loco only operates without pause when the loco enters on the straight through route or when it enters or exits on the divergent route. So, you say that the only time the pause occurs in when the loco exits the reverse loop on the straight through route.

When the loco exits the troublesome reverse loop on the straight through route, it pauses at the gaps, then proceeds. Is it a short or is it a stall? To my way of thinking, it is a short, a momentary short, not a dead short, because it starts up again on its own without any assistance.

It could be the result of a lot of things: faulty wiring, incorrect or insufficient placement of gaps, PSX settings, the turnout itself, the loco. My educated guess is that there is a conflict between the circuit breakers. You have four circui

7

[%-)]

8

I’m just an interested bystander trying to learn, but what would be the fault in the turnout that would cause this behavior?

9

  1. Do you have more than one loco and does this happen with more than one of them? I’m raising this in case it could be an issue of loco wheels shorting across opposite polarity part of the turnout rails. This can happen with Walthers-Shinohara and peco (IIRC) turnouts, don’t know about Atlas.

  2. Can you confirm it’s not happening when any metal loco wheels are crossing the insulating gap? If so, are the gaps on the opposite rails straight across from each other or slightly (1/8" or so) staggered, which is often recommended for a reason I can’t recall? EDIT: I think you addressed this above, when you state the reverser has operated when the first loco wheels hit the gap when approacing the turnout to exit the loop.

Just wanting to surface a couple possibilities, for elimination.

10

Rich, Henry, Paul - It is not happening when any metal loco wheels are crossing the insulating gap. I only have one loco to work with at the moment.

I tried sending the loco through without any cars attached. It happened, but the pause was miniscule and the loco just kept going. The pause is always after the insulators.

I tried going through fast and slow. When I went fast it always stopped and then continued. When I went slow I think I actually went through without a problem at least once.

My newest problem is I’m getting loopy.

11

I say the turnout did it, in the train room, with the candlestick!

So, it is a problem outside the electrical reversing section, on the turnout, part of the center electrical section / “mainline”.

In general, I wonder if it is possible to determine whether it is a shorting problem or a power interruption problem.

Does this “mainline” (between the reversing sections) have its own circuit breaker as Rich noted? Does that circuit board have a LED indicator or point where one can be added to blink when there is a short? Rich, can the Atlas tracks exhibit the wheels bridging opposite polarity rails shorting problem?

What is the loco? Is it possible that it is losing power at a given point on the track? I have a GP9 that was my most sensitive one regarding loss of power and resulting sound hiccups at certain parts of the track where other locos did fine. (I solved that problem by adding a capacitor). That loco would act up more when the wheels were not cleaned, since it was sometimes relying on one truck (at least on one rail). Can you borrow another loco to try? It might not short across rails as easily (depending on wheel profile) if that is possible, or it might not lose power as easily.

Is the turnout nice and flat so that a combination of slightly dirty loco wheels and twisted turnout are not causing one truck to lose contact due to dirty wheels and the remaining truck to have interruption due to twisted rails?

I’m groping here.

12

Okay Paul, I have some info for everyone on this. I got a call from Atlas today and we went over this. The engine I have is a GE Dash 8-40B. I have no idea what all that means and Rich had it correct in terms of the circuit breakers I am using.

I am not experiencing a short. I am experiencing a power interruption problem. Apparently this can happen with Atlas turnouts. The fix is to power the frog. Luckily I got the Atlas turnouts that allow you to power the frog.

Having said all this, I am going to wait until I have another loco to see if this is a problem with that too. The Atlas tech said this is a common problem with locos that have a short wheel base, but that it can happen with other ones as well.

I have also discovered that I can make this problem worse or somewhat better by playing with the track. I have the track nailed down on top of a foam trackbed. The foam has some play and the nails may be too tight.

All of the circuit boards have leds that will blink if there is a short. None are blinking.

13

I am pleased to see your determination in solving these puzzles, and in the responses to your various questions. We have a lot of good will on this forum. I hope you can clear this up.

I hope you don’t mind an aside about your general power management. Why the circuit protector in the mid-section? Your NCE system protects your setup well all by itself, but it can’t reverse the two ends…that’s why you have the two PSX-AR’s. If you were to simply power your entire layout, which you claim is modest in size, by connecting to the mid-section, your NCE system does the circuit protection for you. From there, bi-directionally, the power extends to your loops, but the polarity mismatches are further managed by your AR’s. That is what I would do.

I assume your rail lengths on either side of the NCE unit would total about 20’, including the loop, maybe somewhat more? I don’t see why you couldn’t make a T-shaped bus, run the ends of the top part of the T to the PSX’s, and let them power their respective loops. A proper gauge of wire chosen for the bus will not impose a loss of more than about 0.4V over the distances I envision.

14

Hello Selector - I don’t understand all that you are saying but I can answer some questiosns you asked.

I use a PSX-1 for circuit protection on the main layout because that is what the tech staff at NCE recommended.

I have a star bus. There are multiple power connectors going from it to my tracks. I have tested the voltage and current all along the rail and it is constant - no dropouts.

I am not having any problems with shorting or reversing the polarity. The problem I am encountering on the one turnout is due to a momentary loss of power when the locomotive goes over the insulated frog.

The turnouts I have allow for powering the frog. Atlas recommends doing this with snap relays. I have snap relays in place already. The big question I now have is how to wire the frog. I believe Atlas’ instructions are for DC setups.

Atlas shows you pulling track power from inside the loop. Since this is DCC and since my track power in the loop is reversing automatically, I wonder if I should be taking the power from inside the loop or outside the loop before the turnout.

15

If it were me, I’d put my two leads from the NCE unit out to a T bus. The central section between loops would get a pair or more of ‘feeders’ off any convenient place along the T bus.

Then, where I would have the T’s ends terminating, somewhere near the centers of the loops, I’d feed the PSX correctly with two feeders. The outputs of the PSX’s would supply the loop between the gaps in the rails (your loop IS gapped, right…at the turnout that completes the loop?)

I might only need one pair of feeders to power each loop on a smaller layout. In my experience, one pair of 22 gauge feeders can safely and effectively power about 10’ of rail, provided the feeders themselves aren’t also longer than about 18" or so (they’re thin at that gauge and they’ll resist voltage severely if you cut them too long).

To summarize, NCE unit outputs to the top of the T. The top’s ends run left and right to feed the PSX’s, by thinner feeders if necessary to fit into the terminals. The PSX’s are somewhere near the apex of each loop, and their outputs feed the rails there…short feeders, but longer rails on those loops. It should work. If you get a short anywhere, the PSX’s should be set (by you) to trip if the short happens in their ‘turf’. Or, outside the loops, in the main section your NCE unit is powering directly, it will detect and cut off shorts…at least, that’s the way my setup worked on my last layout. I let the DB150 Digitrax base unit run the layout, but my lone PSX controlled only the part of the reversing loop between the gaps in the rails.

If your rails are fed properly, the DCC signal and voltage ratio will always allows the base unit to detect faults and cut power to the rails. With your two PSX’s where you have them, they’ll look after the portions you have assigned to them. So, I can’t say I agree with the NCE rep saying you need

16

Hello Selector - the problem I am having has nothing to do with shorts or my basic track wiring.

The Atlas turnouts have insulated frogs. Apparently when my locomotive goes over this one particular frog it loses power. One solution is to power the frog. I am not sure how to do that. I am not sure whther to take the power from inside the loop or outside the loop.

I could also try replacing the turnout and hoping that a new turnout will not have this problem. None of my other turnouts have this problem.

17

You have to change the polarity of the frog when yopu switch the turnout. By far the easiest way to do this is with a product called The Frog Juicer. It works the same way as your auto reverser - when it detects a mismatch in polarity, it switches.

You can find them here:

http://www.tamvalleydepot.com/support/frogjuicers.html

18

I have started a new thread with a more specific question on this topic.

19

For goodness sake, Brendan, before you go off powering the frog, make sure it is the turnout that is at fault. If the same type of turnout is performing properly in the other reverse loop, swap the two turnouts and see what happens. That is how to begin to solve the problem, not by going in six different directions. You say that you cannot do this anytime soon. In the time it took to start another thread and call Atlas, you could have had this done.

Rich

20

Says who? I do think that Selector is on the right track, and it is an issue that I have raised in your other thread.

First of all, it most likely is a short, but whether it is a short or a stall, that is something that can be determined relatively easily. To simply state that it is not a short and has nothing to do with your basic wiring, is to refuse to accept the very advice and suggestions that you are asking for.

Second of all, Selector raises a valid issue about the supposed need for a circuit breaker on your mainline (the section of track between the two reverse loops). While you could install a PSX-1 on the mainline, it is not necessary since the Power Cab booster protects the mainline in your layout configuration.

Here is something to think about. When you wire one or more PSX-AR’s (or PSX-ARSC’s) into a series of power districts that also include a PSX-protected power district, the PSX-AR’s (or PSX-ARSC’s) should not be wired downstream from the PSX. If they are, the very result that you are experiencing can occur, that is, a momentary short until the competing circuit breakers resolve the short. Meanwhile, to protect your layout, the Power Cab booster shuts down the system until the conflict is resolved.

So, it very well could be your wiring, and it probably is a short. It is hard to imagine a Dash 8-40b loco staling on an unpowered frog - - - unless one of the trucks is not receiving power (another possibility). I have three Atlas Dash 8-40b diesels on my layout and over 100 unpowered frogs and no stalls.

Rich