Hello,
I’m thinking about adding a crossover to my existing layout, but am concerned about “reverse loop” implications. I run all of my trains using DCC only (Bachman Dynamis DCC). Shown in the picture below is a very basic illustration of my mainline with the crossover in question. What components, if any, do I need to make this work so that polarity isn’t an issue. I would like to make this as simple as possible with no operator type moves on my end (throwing switches). Is this possible? Will I be able to run trains in either direction to each other if I want and not have worry about anything, other than them crashing into each other?
I would imagine a DCC auto reversing module would be all you need. It’s been the topic of a few posts lately and exactly how it works I can’t say but it does the polarity switching for you. I am only assuming that it some how sense the direction of the locomotive and switches the polarity of the track wiring accordingly.
Here is a link to Tony’s trains one of the dcc guru’s of the hobby I am sure a better explanation of how it functions can be found there.
You only need one and yes, you can use other brands. I showed you that one because you have Bachmann now. If you follow these posts you are probably aware that I am not a fan of Bachmann.
I prefer, and use, Digitrax, but there are several really good brands available and the choice is a personal preference.
DCC is symmetrical, the engine does not care about polarity. The auto reverse module is there to prevent short circuits when the track loops back on itself and while the powered units are crossing the boundary between segments where the polarity is reversed.
Thanks again Phoebe Vet,
I understand where you are coming from about Bachmann. The Dynamis works “ok” for my needs right now and was the cheapest of the bunch. BUT…I can see moving on to Digitrax, MRC, or one of the others down the road.
I have just one more question about this reverse loop thing though…well actually two. (1) It almost seems to me that you need two modules because each end is a reverse loop? (2) are there any special concerns with switch machines controlling the crossover turnouts that I should be aware of?
All that is important is that the two sections are completely isolated from each other. The auto reverse module, when it senses the short as the engine passes across the gap, will reverse the section that it controlls to match the polarity with the one it doesn’t control. It does not matter whether the train is entering or leaving the controlled section. If the two sections already match, it will not do anything.
I highly recommend Digitrax. I have the Super Chief.
Um…make your gaps further up the balloons (cut off the tops of the balloons, if you will). You need to make your reversing loop as long as your longest train, and the suggestion to just isolate the crossover will NOT work as a reversing loop modual cannot handle a short at both ends. You need 2 reversers for this layout.
Perhaps this diagram is clearer. The blue side controlled by the auto reverser. At no time would the train be crossing two transitions at once, and I doubt that he would be running a train longer than the blue section since it appears to be about a third of his mainline. It WILL work, and you only need ONE reverser.
Maybe it’s my fault. Perhaps I did not make my diagram clear enough. I don’t think you understand where I suggested the OP put his 3 breaks in the track. There is no very short section. It is not possible for the train to cross two of the breaks without going around one end of the mainline or the other.
If he had drawn a double crossover, it would be different, but he did not. Check his original diagram.
One thing has me a little puzzled, would the reversing loop only be required if the train were to change direction correct? If the train were to travel from the outside loop to the inside loop still continuing in the same direction a reversing loop would or would not be needed?
If you install the crossover then you will need the auto reverser. The switch will cause a short if it’s not insulated between the switches, and if it is insulated, the train passing over the switch will cause a short. The auto reverse module, with the three electrical breaks I described, will make the proper polarity changes to the loop to which it is wired when it detects that short.
As Dave B said, the loop must be longer than the train and the loop that is controlled by the reverse module must be isolated electrically from the rest of the layout. It will be if you put the breaks where I showed you.
Hey all,
Great discussion going on here! I really appreciate all of the help and input. I have my crossover just about done. Just waiting for the glue to dry to move on to install the auto reverser. I have one more concern…Will I need to add power feeders to each turnout in the crossover, between the frog and the insulated railjoiner between the two turnouts? my thinking is that this area becomes a dead zone which may stop a locomotive as it goes through the crossover.
Well, I got everything hooked up for my crossover and BAM!..recieved a short-circuit as I ran my loco through the crossover.
I’ll refer you to the illustration of portion of my layout below. As you can see, I hooked up my MRC auto-reverser from what I thought was the correct way (notice the blocks placed within the crossover). The directional arrows show the direction the trains go to perform the “loop”. The yellow dashed lines indicate that I also tried installing the yellow wires from the auto-reverse unit there…again with no luck. I’m lost and a little frustrated.
Just a little more info for you. The crossover consists of (2) #6 Walthers/Shinohara “DCC ready” turnouts. The rest of the track is Atlas flex 83 and custom-line turnouts. All other tracks shown end in “stub end” yards.
Where do you have the output from your command station wired to? It should only be wired to one of the loops(whichever one is wired to the input to the auto reverser. If you already had it wired up to both loops and did not remove it from one of the loops you will still get a short.
I agree with CSX Robert. The section that you have set up to be the reversing section must be powered ONLY by the reverser, otherwise when the reverser changes the polarity of the power going through it it will cause a short through the reverser.
