General Information: I’m modeling in HO and using the NCE Power Pro R DCC system.
My layout is basically an around the walls layout with a center teardrop island. In the center island area I plan on having a few industries. The problem is, the center island is also a reverse loop.
My question is: Since the industries are inside the reverse loop, will I have problems with polarity changes when switching the industries if I have a train coming into or leaving the loop while at the same time I am switching the industries with another loco?
Since I’m using DCC should all the loco’s that are in the loop switch polarity without notice?
I will be using Tony’s PS Rev Power Shield Intelligent Reverse / Breaker for automatic polarity changing.
If your reverse loop is simple - just a single track approaching a turnout from the point end, and then a loop from one track to the other at the frog end, you should have no trouble. Any track which is wholly inside the “protected” reverse area will work fine, and you won’t notice the polarity flips at all. There are only a few issues that I’ve found with reversers:
If you can cross both ends of the loop at the same time, either with locos or metal wheels, then you can have a short at that point. Think of an oval with a diagonal crossover. In that configuration, the two insulated gaps are separated, but either the same train or two different trains could be over both gaps at once. An auto-reverser can’t handle this.
The Tony’s reverser (one of the best, by the way) has a current limit which may be less than your DCC system as a whole. I’ve got an older Tony’s PS-REV, and it’s got a 2-amp limit, while my DCC system will run 5 amps. So, you are limited to 2 amps inside the loop. In all probability, that will not be a problem. You should be able to run 4 engines comfortably. Any engines running outside the loop don’t count towards the 2-amp ceiling.
DC engines will not work properly with auto-reverse. They still depend on track polarity, even when running as Engine Zero on DCC, so they’ll reverse direction when the polarity of the loop flips. All the more reason to convert all of your engines to DCC.
The auto-reverser is also a circuit-breaker. So, if you have a short inside your loop, the loop and other associated trackage will shut down, but the rest of your layout will keep running. That’s a good thing, of course, but the first couple of time it happens you’ll wonder why the trains in the loop aren’t running, while the rest are.
To answer definitively one would have to see the exact track layout. However, in general, the answer is no. A second train on the loop should not be affected by the loco switching the industries or vice-versa. If there is some configuration present in the track where both the switching loco and road locomotive could cross (be spanning) opposite ends of the loop at the same time is when problems would occur.
The locomotives will not be impacted by the polarity shift that occurred in their power source. Their decoders will notice it, but immediately adjust and someone operating the locomotive will not notice anything happened.
P.S. There are many threads on reversing sections and DCC over in the “Electronics & DCC” sub-forum.
If the way I am seeing it is the way you are describing it, you should be fine so long as your insulation gaps don’t include any of the turnouts to industries or industries in the reversing section. Because what an auto reverser does, is takes current from the main part of the layout, look for shorts when a train enters the reverse loop, and swaps the polarity to the reversing (insulated) section as needed. Typically you want your reverse loops to be as long as your longest train, plus a few inches, but I suppose as long as your longest locomotive–or consist of locomotives would work. Though there may be problems with metal wheelsets shorting out the insulated sections.