Sunday, May 3, 2015

Experimenting with reverse loops

The design of this layout includes 2 reverse loops to turn trains around in the staging yard at the west end of the layout.  For those not familiar with reverse loops, here is a LINK to an article that explains it well. As I am moving along on the staging yard I realized that I have had very limited experience working with reverse loops.  I decided to use my already existing temporary layout that is on a shelf above my work bench to get that needed experience.  The layout uses Kato Unitrack so the changes would be easy.

There are several products available to work with a DCC system that handle the polarity switching that has to take place.

As I had already worked with DCC Specialties PSX-1 circuit breakers and have been quite happy with them, I decided  to order their PSX-AR reverse loop circuit breaker to experiment with. This products senses the short that occurs and does the switching before the short gets to the DCC system.

I thought the simplest way to make a reverse loop would be to put a crossover in the middle of the loop.  But as I soon found out, this is actually two reverse loops and my test engine would stall when crossing the gaps.

Realizing that as long as there was a standard non reversing section in the middle, both reverse loops could be connected to the same PSX-AR.  So the next configuration was a double crossover as shown in the drawing below.  What I really liked about his arrangement was that it is almost identical to what is at Wesso junction and will be modeled on the main layout.

In this configuration the single engine ran fine through any turnout configuration but when I started a second engine it caused the stalling problem whenever both reached gaps at the same time.

So next a second PSX-AR was added as shown in this drawing.  Same test done with two engines running independently.  This time no hesitation when both were crossing the gaps at the same time.

The existing temporary layout had consisted of an oval that used 11 inch radius curves.  The layout shown in the drawings above used 9-3/4 inch radius curves and fit inside that existing layout.  Then I added a double crossover connecting the two loops and also added a siding along the back of the outer loop so there ends up being quite a bit of track in the small space.

Here's a view of the central part of the modified temporary layout where all the turnouts are.   Beyond this on either side is a double track balloon end.  I've been running up to three short trains at a time to test everything.  There can still be a stall if one engine is leaving a reverse loop section at the same time another engine is entering the same reverse loop section.

All three PSX circuit boards are mounted on a scrap of plywood on the wall under the layout to make it easier to see the status LED's on the boards.  There is also a provision on these boards to connect remote LED's as well as many other features that I have not yet explored.


  1. HI Brad.
    I have two PSX-AR auto reversers to install on my new HOn3 layout. Neither of them work out of the bag. I am sure we have wired them correctly and we are going to take a look this arvo. The seller suggests that I do a whole lot of tests as per page 3 in the manual. Any clues?

    1. Sorry to hear that Rod. I looked on page 3 and did not see anything I would call tests or trouble shooting instructions but here is what I would do.

      Connect the PSX-AR to a section of track by itself and verify that it passing power by running an engine. Like this it should operate just like a PSX-1. Place a short on the rail to test circuit breaker function.

      Be sure that both rails are fully gapped at both ends of the reversing section. I just fixed a problem on my movable end loop that has been bugging me for months. What I found is that I could not rely on Kato track insulator joiners to fully isolate DCC signal and made my own gaps. DCC signal does not behave the same way as regular DC and seems to be able to bridge small gaps. The PSX instructions state to stagger the gaps by 21mm but I have not done so and have not had a problem.

      Good luck and let me know how it goes. Email me at