So about this reversing loop thing

[rsn48]

I'm hoping this is my last revering loop question, at least until my upper level goes in.  Almost embarrassed to ask this one, I know I'm going to say - "DOH!" - after I get the answer.

So in the thread, Help Me Find the Reversing Loop, I decided to have a large and extensive reversing loop.  When I installed the track years ago each one was gapped with styrene with the feeders to each and every track and turnouts, these gapped as well.  Now in my head a reversing loop makes sense if the track are "all one" in terms of metal joiners making the loop acting as "one."  But if I have each track its own "block" when the OR-AR (the poor man's PSX...) is thrown, won't just that one track that is isolated (its own block) be thrown only.

I have a 14 black and white house hold wiring bus underneath, I have thought if I chop the wiring so that the wiring is set up for that reversing loop only, something I was going to do anyways as a PM2 circuit breaker district will this work or am I over thinking something simple.

[Bangorboy]

You're right!  The OG-AR will reverse only the tracks connected to its output.  So in your stated example only the one track will be protected from polarity (actually phasing) mismatches.

You can put the reverser before the PM42, but then you need to consider...

The PM42 can give you overcurrent protection for four districts.  However, if all of those districts are below the cutoff threshold and the PM42 doesn't shut down, you could still exceed the current capacity of the OG-AR or other reverser with all those trains in the large reversing section you depicted in the other thread.  This is especially true if you have a lot of locos and lighted cars sitting in those two yards.

Those double tracks down the left wall look quite long.  Do you think you will actually have trains long enough to bridge the gaps at both ends of those double tracks at the same time? 

If you had a passenger train long enough to have the engines bridge the gap at one end while lighted passenger cars are still bridging the gap at the other end you would have direct short that the reverser (OG-AR or other) cannot resolve.  If none of your trains can be this long, the reversing section does not need to include the yards and the associated amperage load issues. 

If you use one reverser for both paths on the double track, you'd have to be careful not to have a train entering one track at the top while another is entering the other track at the bottom, though.  The easiest solution is to have two reversers, one for the southbound and one for the northbound of the double tracks, and prohibit trains from entering either track until the previous train has cleared.

Bottom line, don't overload the reversers, and make sure nothing bridges the gaps at BOTH ends of any reversing section at the same time.

Bill B
N Scaling in South Okaloosa

[rsn48]

So if I cut the bus so only the area I have indicated is covered by that bus, for lack of better words, can I throw the bus?  The OR-AR has its own circuit breaking.

Here is the best chart I could find about AR's:

DCC in Reversing Loops

Operation and wiring of a reversing section has always been a big mystery for most modelers. The problem is that somewhere in the loop the polarity of the rails reverses and when the metal wheels come to the rail reversal, there is a short circuit. Fortunately with DCC, because the decoder determines the direction of a locomotive, and not the polarity of the rails, the polarity of the loop can be “flipped” while the train is in the loop. This has lead to the development of DCC “Automatic Reversers” that allow the loop to be automated. These Automatic Reversers work by sensing the short at the gap and reversing the polarity quickly.

Types of Auto-Reversers

The polarity can be switched using either Relays or Transistors. The advantage of transistor type auto-reversers is high speed switching and no mechanical contacts to arc, pit and fail. Also, there are no sparks at the reverser gaps to cause wheel pitting. A reversing loop is not immune from derailments or someone neglecting to throw a turnout (shorts happen). This means the reversing loop needs to be protected from a short circuit with a circuit breaker. Some reversers come with built-in circuit breakers. If you are using a low-power system 2 Amps or less, be sure the circuit breaker trip current is less than the low-power rating of the DCC system. Also, check that the reverser will reverse the polarity at the lower current without shutting down the DCC system.

Product                                          Digitrax                     Lenz        MRC         Tony’s        DCC Specialties
Features                                     AR-1     PM42               LK100     AD250      PSRev        OG-AR       PSX-AR (11)
Unit Cost (List Price)                $29.99    $80 / 23 (1)    $57.00   $34.95         $56.95     $39.95      $59.95
Trip Amps (2)                        0.25 to 8    1.5 to 12        1 to 10    2 3.8 to 8     4               4              1.27 to 19.1 (5)
Built-in Circuit Breaker             No            Yes (3)             No         No               Yes          Yes            Yes
Response Timing (6)               Slow           Slow               Slow       Slow           Fast         Fast          Fast
Manual Reset Optional          No               No                   No          No               Yes          No             Yes
Programmable Settings         Adjustable  w/DCC System Knob      No              Jumper      1              Jumper or System
Status Lites                           No              Yes                   No           No               Yes          Yes           Yes
Method of Switching Power    Relay        Relay              Relay         Relay     Solid-State   Solid-State Solid-State
Extra Power Supply Needed   No             Yes                 No            No          No               No               No
Network Feedback                  No              Yes                No            No          No               No               Yes
Spike Current Inrush Control (7) No        No                   No            No         Partial          No               Yes
Integrated Stationery Decoder [8] No      No                  No            No         No                No               Yes
Integrated Block Detection (9]  No            No                No              No         No                No                Yes
Annunciator Output (10)           No             No                No             No         No                No                Yes

(1) The PM42 has 4 outputs, so the cost ($80.00) plus power supply ($12.00) equals $92.00 divided by 4; (2) Some units have adjustable trip current settings; (3) PM42 also requires outputs for short circuit protection when using Auto Reverse (4) Special units for low-power DCC systems are available; (5) Currents over 10 Amps require added heat sinks; (6) Slow is in milliseconds (1/1,000) and fast is in microseconds (1/1,000,000); (7) Start-up of Sound Locos creates 4-8 Amp spike currents; [8] Automates reverse block turnouts with integrated stationary decoder; (9) Block Occupancy output for LEDs and Networks; (10) Off the shelf, Status Annunciator option; (11) Patent pending.

Rules for Reverse Loops and Reversing Sections

Auto Reversers can be used for sections of track like wyes, turntables, and loops. Some general rules that apply: 1. The reverse block track must have double gaps at both ends and be totally isolated. 2. The length of the reverse section should be longer than the longest train to use the section. If the track is shorter, wheels can contact on both ends gaps shorting the reverser. There are special gaping procedures that permit having reverse sections shorter than your longest train.

[Bangorboy]

Yes, you can separate the area you indicated from the rest of the layout by cutting the bus, since you already have the track double-gapped at the turnouts at both entrances.  You connect the disconnected bus to the output from the OG-AR (On Guard - Auto Reverser).  ... Uh, you keep saying OR-AR.  You are talking about the OG-
AR in the chart you supplied, right?...

I'll make one more pitch for you to be cautious about the total load you place on the OG-AR if you make the whole lower section of this layout one bit reversing section.  The OG-AR has a 4 Amp capacity.  If you park a lot of passenger trains with lights and/or a lot of locos in the yards, and add more trains along the mainlines, they will all be adding to the demand.  If you have sound decoders, the OG-AR does not have provisions for the inrush current at startup.  You may end up having to wire in switches to shut of all the yard tracks and turn them back on individually.  (This could have some advantages, for that matter.)

If you have problems with the above, consider isolating just the tracks along the left wall.  I'm sure the OG-AR will handle that without issues. 

Good luck with your efforts.  It's always nice when a plan comes together.

 

[Bangorboy]

One other thing -- If you decide to go with PM42 reversing, remember that a section of the PM42 that is programmed as an autoreverser is no longer giving short protection (circuit breaker).  And it is not recommended that the autoreverse section be short protected by another section on the same PM42.  Use a different PM42 to provide the short protection.  Just a comment, since you seem to favor the OG-AR.

[rsn48]

Bill, Santa is bringing me two OG-AR (my bad about saying OR) reversers.  So now I'll have two PM42 boards, 8 circuits for a smaller layout....lol!