3-Way Turnouts - Reverse Polarity

Model Railroader Electronics and DCC
1

I am baffled with this one. Check out my track diagram. The red dots are gapped rails.

I have three Walthers Shinohara 3-way turnouts lined up end to end on my DCC powered layout.

My auto-reverser, a Digitrax AR-1, is clicking as a loco crosses over the second and third 3-ways, as you look from left to right. Is the gapping that is built into the 3-ways causing the AR-1 to reverse polarity. I hear the clicking twice, once on the second turnout and once more on the third turnout.

At first, I wondered if the AR-1 was acting up by through various tests and swaps of another known good AR-1, I am convinced that it is not an AR-1 issue.

I would not expect to hear any clicks as the loco traverses the three 3-way turnouts.

I also have another curious issue. I have a BLI E7 that prompts the AR-1 to click when I press forward and again when I press reverse on my throttle. This does not happen with other BLI E7s inside that reversing section. I try that BLI E7 on a different reversing section on my layout (a straight section of track) and that clicking on forward and reverse does not happen.

HELP!

What is going on here?

Rich

2

Just a thought, check to see if a wheel tread is bridging the rails coming out of/near the frogs. Sometimes this can be fixed with a shim on the guard rail.

Edit, also check the wheel gauges and compare the locos too.

Richard

3

LION would want to see more of the layout. What are these main lines. Are they east bound trains on the bottom and west bound trains on the top or are there east and west bound trains both top and bottom?

Do the main lines loop together somewhere off of your picture, in other words, to they go around the turntable and round house so that the lower tracks become the upper tracks as they go around the roundhouse (or elsewhere).

How are you applying your power? LION (using DC) powers all of his tracks for the forward direction of travel thus the outer loop and the inner loop would be powered in opposite directions. Finally are those “crossings” or are they “slip-switches”.

The LION would gap the heck out of this thing so that the center track where your first dot on the left is receives its power ONLY from the track that is aligned to it and all other tracks are gaped out. LIONS know nothing of DCC, but him does know a reversing loop when he sees it.

OTOH, if all of these tracks are wired for service left to right, then there is no problem on this layout.

ROAR

4

Rich, There seems to be some missing elements from your drawing.

  1. Where are your track feeders located?

  2. Where is the Auto Reverser connected?

  3. Why do you need an Auto Reverser here? (I don’t see a reverse loop.)

5

If these are the ‘older’ power routing turnouts, you do need a set of gaps on the frog end of each route. Your 3rd to the right 3-way does not have the gaps.

If this is a newer ‘DCC Ready’ turnout, you should not need the gaps as the frogs are isolated. How-ever, I always ‘gap’ mine on the frog end anyway, just to make sure.

One thing that does happen is that a metal wheel set that has very wide tires may ‘bridge’ the gap where the two rails join just above the frog. I have seen this happen with Peco ‘Insul-Frog’ turnouts. The quick fix is to ‘paint’ that tip area with clear paint of clear finger nail polish!

As far as that BLI E7 - if they are older ones with the QSI sound decoders, they can be real power hogs with ‘in-rush’ current when they start up or lose power and start up again. This large capacitors in them can play havoc! On or club we have one reversing section that used an AR-1 and if you have 3 of those E7’s in a consist - the AR-1 chatter or hangs up. If I adjust the small ‘pot’ on the AR-1 to handle the E7’s, then smaller engine do not trip the AR-1 reliably. I just got a PSX-AR to replace the AR-1 as a ‘test’. I plan to install it Wednesday and will report back.

Jim

6

Lots of good comments and questions here.

I believe that I failed to provide enough information, so let me add some detail.

I revised the track diagram to make clear where those double main line tracks are coming from and going to. The double main line continues left at the top around the passenger station and returns on the bottom headed right. All of the tracks are wired "in phase, so the “outer” rail is wired one way and the “inner” rail is wired the other way. So the approach tracks to the station coming off the main line at the top cause the reverse polarity problem, a reverse loop, if you will.

Those are crossings, not double slips, from the outer main line across the inner main line.

All of the turnouts and crossings are DCC friendly, none are power routing. No Frog juicers or anything like that. The gaps are intended to complete isolate the reversing section which includes the entire coach yard and the four approach tracks. There is one feeder wire on each coach track. There are rail joiners connecting the 3 ways, but no feeder wires. Each approach track has feeders and the single lead headed toward the station has feeder wires. All of those feeder wires are inside the reversing section and all connect to the output side of the AR-1.

I do not have any dead shorts. But, I do get the clicking over the 3-ways, so for some reason, the AR-1 senses polarity changes.

Regarding that troublesome BLI E7, it is an older one with QSI sound. But similar older BLI E7s with QSI sound do not act up in the same way. Only that one clicks the AR-1 as I toggle between forward and reverse and it does it in the coach yard on flex track away from the 3-way turnouts.

Rich

7

OK. Now I assume that where you are showing the dots for gaps, the track is double gaped. That is, both rails are gaped and none of them has closed up.

Next . . . I would gap 5 more tracks. (Now these may not be strictly necessary, but if I were putting this track arrangement down on my layout, I would do it just as a possible safety measure, even if I had to add feeders later because of non powered rails that were created by these gaps. The Shinohara three-ways I had were power routing. And since you seem to be having a problem, it couldn’t hurt. Just extra work, but still not guaranteed to fix the problem. I would also be using an electronic AR-breaker combination device and not one that uses a relay. (Also saying that that may not be the problem either.))

  • Three gaps on the output tracks of the last three-way to the right. Double gap each track. Then add the feeders necessary for power in the coach yard, still connected to the output of the auto reverser.

  • Then double gap the center track out of the two remaining three-ways. Then feed power from the output of the AR to the point end of each three-way.

So why would I recommend this? Depending on the power routing setup and / or hidden jumpers within the three-way turnouts, there may be some conflict that isn’t readily obvious. Electrically, you should end up with the same polarity on the rails, but you have eliminated the possibility of one output tracks rails being connected together when the route is not set for that direction.

I hope this helps.

8

Elmer, thanks for your comments and suggestions.

Yes, those red dots indicate double gaps, both rails.

I will study your suggestions. It may not accomplish anything though because the entire reversing section is isolated by the existing gaps, and I am not experiencing any dead shorts.

I have two thoughts as I read through the replies including yours. One is to add feeders between the first and second 3-way and between the second and third 3-way. Two, check closer to see if the wheels are momentarily shorting against the opposite rail at the frog, causing the AR-1 to flip.

Rich

9

Because your AR-1 is not a breaker, how will you know if there is a track short within the reversing section? If it is a momentary short, you will hear the relay click.

How do you know that the AR click has actually flipped the polarity when it clicks with a locomotive going through the three-ways? You will not be able to tell by the actions of the locomotive. The only way that I know of is to connect some kind of test device that would show you the polarity. This could be as simple as a couple of LEDs or a digital volt meter. You would have to measure across the gaps at several places, but I would think you could measure or put LEDs on the same rail, or opposite rails, or both, from the main into the reversing section. Then when the reverser flips, the LEDs would change. (Don’t forget the resistors for the LEDs.)

10

You do not need a gap at the turntable, the station gap should be moved to the yard lead.

Establish the following logic for your system:

  1. Only one switch can be aligned between the station and Any of the main lines OR yard and Turntable.

  2. ONLY the selected route provides power to the station track.

What you have in essence is a station that connects to a yard with and between the station and yard, there are four crossings (four pairs of switches) of which only ONE PAIR can be selected, or no pair is selected in which case it may be connected to the yard power. When any one pair is selected to enter the station the others are isolated from the station track.

Ergo, you have a rotatory switch that can select Main 1, Main 2, Main 3, Main 4, Yard, or OFF. Use relays to align the necessary switches and connect the power to the selected track, they can also display signals.

LION will have to think about it, but I am sure that I could design a fairly simple arrangement that would cause this to work correctly.

ROAR

11

There are only two crossings, one top and one bottom for the outer track to cross the inner track to reach the station or coach yard.

Rich

12

Those are “Diamonds” The cross-overs are between the station track and each of the four main lines.

ROAR

13

Rich

First, I read the diagram as 3 three way turnouts stacked on the straight path. The right end of the coach yard is 2 normal turnouts, and not a 3 way.

Assuming I understand your diagram correctly, I am willing to bet that your 3 way turnouts have a very simplified “truth table”, which ensures correct polarity for the chosen path, and “don’t care” for the non-chosen paths. In reality, the non-chosen paths may or may not be power routing, depending on the exact wiring. Therefore, the third three way is capable of having mis-matched polarities, depending on how the 2nd and 3rd three way are thrown.

The way to check would be to isolate a Walters 3 way turnout, power the point end, and measure the polarity of each of the 6 diverging rails with each path selected. If I am correct, you will not see correct polarity on all six rails for each of the 3 paths. Typically, polarity will be correct for 2 of the 3 paths, but not for the 3rd. This is especially true when the selected path is not the center path. Usually, two of the three frogs are electrically one unit, which causes the unusual polarities.

my thoughts, your choices

Fred W

14

OK, I solved the problem, but more through trial and error than logical reasoning.

I noticed that the clicking of the AR-1 occurred whenever the front truck of a loco was on one 3-way turnout and the rear truck was on another 3-way turnout with the rear truck passing the guard rail near the frog. Interestingly, it was not happening with short wheelbase locos like an S-1 switcher.

Anyhow, what I did was to turn the TTC scew clockwise on the AR-1. After a one quarter turn, the clicking no longer occurred. OK, so that fixed the problem, but why?

In the past, I have installed 3 other AR-1’s on my layout but all for short sections of track. I never have had to adjust the TTC in the past.

But I only recently installed the coach yard and those station approach tracks off the main line that you see in the diagram. Today, I began serious testing of all of this track work. As I mentioned, there is not a dead short. The gaps seem adequate and complete, and there was no bad wiring.

The instruction sheet for the AR-1 says that it will trip one time at the beginning of the reversing section. It should not trip more than once while the loco is in the reversing section. If it trips more than once, the trip current is set too low and a clock wise adjustment of the TTC screw should be made.

The instruction sheet goes on to say that “the TTC adjustment is made using a full load on the reversing track - - the total number of locomotives/cars that will be in the reversing loop”.

Since my other reversing sections are short, only one loco at a time is in the reversing section. But this reversing section contains the entire 8-track coach yard and there are several locos at a time parked in the yard. Is that the problem? The more locos, even if parked, the greater the TTC adjustment?

I will still have to fine tune the TTC adjustment because even though the clicking of the AR-1 has sto

15

It wouldn’t hurt. If you don’t have feeders there now, then power is being routed through the turnouts and possibly the points, from the first one and on to the next ones.

16

Yeah, your’e right, Elmer. I will wire in feeders tomorrow, Thanks.

Rich

17

[quote user=“fwright”]

Rich

First, I read the diagram as 3 three way turnouts stacked on the straight path. The right end of the coach yard is 2 normal turnouts, and not a 3 way.

Assuming I understand your diagram correctly, I am willing to bet that your 3 way turnouts have a very simplified “truth table”, which ensures correct polarity for the chosen path, and “don’t care” for the non-chosen paths. In reality, the non-chosen paths may or may not be power routing, depending on the exact wiring. Therefore, the third three way is capable of having mis-matched polarities, depending on how the 2nd and 3rd three way are thrown.

The way to check would be to isolate a Walters 3 way turnout, power the point end, and measure the polarity of each of the 6 diverging rails with each path selected. If I am correct, you will not see correct polarity on all six rails for each of the 3 paths. Typically, polarity will be correct for 2 of the 3 paths, but not for the 3rd. This is especially true when the selected path is not the center path. Usually, two of the three frogs are electrically one unit, which causes the unusual polarities.

my thoughts, your choices

Fred W

18

Rich: This may have nothing to do with your problem,but I was having trouble with my three-way walthers turnout,too.Sometimes everything was fine,sometimes I would get a very brief short,and sometimes it would shut everything down… I finally figured out that,occasionally,the inside surface of a wheel would touch the rail outlined in red while running on the rail just below it (different polarities).I cut the jumper between that rail and the topmost rail by cutting through the tie in the green box. Now that short length of rail is dead. The turnout has worked flawlessly ever since.

Mike

19

Mike,

That is the same spot where I am having the problem. As the wheel crosses over that piece of the 3-way, it sets off the AR-1 which is obviously sensing a potential short and is trying to match polarities.

I will take a closer look at it tomorrow.

Thanks for those comments and that photo.

Rich

20

I put this issue aside for a few weeks to work on some other items on my layout To Do list, but I finally got back to looking at this issue last night.

middleman correctly indentified the problem and the offending piece of rail, the small section inside that red box in the photo.

Instead of cutting through the tie in the green box, or using clear nail polish as others have done, I wanted to be sure that the section of rail in the red box was the problem, so I applied a thin piece of masking tape on the side of the rail closest to the rail of opposite polarity. Voila ! That was the problem. No more tripping my auto-reverser.

Thanks to Mike (middleman) and all others who contributed to this thread.

Rich