Reversing Loops and DCC a question


T

thhynes

Member
My question is this -

Imagine two reversing loops at either end of a track...
Imagine that One train is headed to the left, and one is headed to the right - and although I know two objects can not occupy the same space
at the same time, imagine if you will that these two trains are on the Quantum level and can pass through one another.

If one train exits the reversing loop on one side and starts down the straight track
and at the same time, the other train is exiting the reversing loop and entering the straight track
and assuming you have 10 feet of distance between the locomotives...My question is this...

if the train on the left is headed toward the opposite side... does the train on the opposite side
start to go in reverse or is there some sort of short circuit, or do both trains continue heading in the direction they are heading?

If I understand something about DCC, and I could be wrong here... it is the circuit board inside the locomotive receiving the DCC signal that
regulates the train's forward or reverse motion... correct? If so then in the scenario above, both trains would pass through each other, go through the opening loop, and repeat.

If this is correct then I don't need to worry about a polarity change in the rails, as in a DC system, because in that scenario the oncoming train would go in reverse.

am asking this question because I have come across a layout that looks tight in HO but in N scale could have bigger curves, and this layout could potentially have two trains on the same track heading in opposite directions.
 
Reversing loops do not affect the locos. What it does affect is the track polarity, so you have to insulate both rails at both ends of the reversing section. And in your case you would do this for both reversing loops. You can use a manual switch to change polarity while the train is in the reversing section, I would stop the train before moving the switch. Or you can use an auto-reverser such as the Digitrax AR-1 and you would not need to stop the train.

Instead of using quantum trains it would be cheaper to use a passing siding. :)
 
timlange3 said:
Reversing loops do not affect the locos. What it does affect is the track polarity, so you have to insulate both rails at both ends of the reversing section. And in your case you would do this for both reversing loops. You can use a manual switch to change polarity while the train is in the reversing section, I would stop the train before moving the switch. Or you can use an auto-reverser such as the Digitrax AR-1 and you would not need to stop the train.

Instead of using quantum trains it would be cheaper to use a passing siding. :)
Click to expand...
So for my clarification due to my struggles with DCC

The polarity of the rails does not matter in a DCC system as both rails are at a 60hz cycle both positive and negative
it is the DCC chip inside the locomotive that controls the direction of the train.

Maybe I am making this more complicated the it needs to be, but I think of DCC as the following....

12 Volts coming into a POWER "pack" DCC then breaks up the 12 volts into 12 single 1-volt signals and assigns each one a specific address

1 Volt = Address 0001
1 Volt = Address 0002
1 Volt = Address 0003 ---- 12 Volt at Address 0012

Each Address is now a packet of information, like a ZIP file
it is only the Locomotive with the Address 0001 that can unzip the ZIP file of 0001 sent by the DCC system and ignore the others whizzing by.

So if ZIP file 0001 Says move in this direction --> the locomotive moves in that direction, while a locomotive on the same rail
who receives the Zip File from Address 0002 only uses the information contained within that ZIP file named 0002...and therefore if the ZIP file says move in <-- this direction the locomotive carries out that instruction

So in DCC, it is possible that two locomotives facing each other moving towards each other in a forward motion would crash into each other, regardless if they came out of a reversing loop or not.

The reason why I am asking is with DCC and watching several videos on the topic, dealing with the loop itself and automating the points within the switch to change automatically is so much simpler it seems than in a DC system
 
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I don't know much about electricity and even less about quantum physics but two trains traveling in opposite directions on the same track (electrically) is no problem with DCC.
 
Thanks for the responses...not that I do not trust people, I did also ask the same question at the Hobby store this afternoon, and he stated the same thing!
 
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If you have dcc, it doesn't matter what polarity the track has, the decoder controls the direction. Any reversing loops, however, need to be insulated from the rest of the track, and if continuous running is desired, an electronic device to control the reversed polarity is needed.
 
The phase conflict is verbotten for all things electrical. It creates a short which allows full circuit amperage to course through the affected area with maximum resistance, meaning the area gets HOT!! Heat kills electrical components. This includes decoders. So, to protect itself, and your costly sound decoders, the nice engineers who designed our DCC systems included short detection circuitry which will shut down the entire track system until the fault is corrected. Reversers switch the phase under the offending axle as it crosses the area where the phase conflict happens. They do this in a few milliseconds which does not affect the decoder and which the short detection circuit in the command unit cannot react to in time and cut off track power.

You can have two trains enter the same reversed loop at the same time. But there are potential problems, not least of which is that the reverser might not correct any one axle's confound in time. The way to get around this is to have two sets of transverse gaps at each end of the reversed loop. The pairs of gaps are as far apart as the length of axles-spacing on the frame or truck. This gapped section with four gaps allows metal tires to enter the gapped area and pass across to the rest of the powered mains without tripping the reverser or causing a short.
 
You are making this way too hard. Reversing loops have nothing really to do with DCC. The problem with reversing loops is the polarity of the current on the tracks, it has nothing to do with the DCC signal.

If you have a pure DC layout you would have EXACTLY the same shorting problem. If you have a DCC layout and lighted cars without any decoder in any lighted car, you would have the EXACT same problem with them crossing the boundary of the reversing section.

At one boundary on a reverse loop you will have a condition where the north rail is positive on one side of the boundary and the north rail on the other side of the boundary is negative.

Shorting of a reverse loop has absolutely NOTHING to do with the DCC decoder, the packets, the signals, anything in the DCC system. It is purely an electrical polarity problem.
 
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