Reverse Loops, Polarity Conflicts & DCC

[jtomai]

(please see Diagram)

I have a simple layout that I plan very soon to convert to DCC, I am currently using simple Direct Current (DC), but any day now I am ordering a DCC system.

I have 2 main lines connected by a reverse loop. Both main lines have the (+) rail on the outside and the (-) rail on the inside, so obviously when Main Line #1 takes a turnout that leads into Main Line #2 there is a polarity issue. I have insulated there, with plastic rail joiners. Still, Loco's stop automatically, because the opposite polarity on the other side of the insulated joiner while using DC power tells them to reverse, while the other half of the loco on the other side of the insulation, polarity sends it forward. (See diagram below)

My question is will the wiring scheme in the image below work for DCC? I want trains to be able to travel any direction, say heading forward on Main #1, and then cross over using the reverse loop (with the polarity problem) to Main #2 heading the opposite way. I want my trains to run through the layout looping trough main #1 and then back to Main #2 in any direction. Will DCC magically solve the polarity issue with the reverse loop?

Is there something I am missing in my current wiring scheme, because I am afraid to lay any more track, and wiring for fear that my wiring scheme is not compliant for DCC. Also, will DCC simply use my existing (+) & (-) feeders & bus lines? Or will I have to add another separate DCC bus and connect feeders from that to my track?

Thanks,

John

 

[fast_ian]

... Will DCC magically solve the polarity issue with the reverse loop?

"Almost" - You're gonna need a DCC auto-reverser in there. Tonys Trains does one that gets generally good reviews or your DCC system supplier will probably also make 'em - Digitrax for example makes the "AR1" which will do the job. An AR unit "sees" a short when your loco switches sections, but rather than shut down it (very quickly) switches the polarity as required.

Is there something I am missing in my current wiring scheme, because I am afraid to lay any more track, and wiring for fear that my wiring scheme is not compliant for DCC. Also, will DCC simply use my existing (+) & (-) feeders & bus lines? Or will I have to add another separate DCC bus and connect feeders from that to my track?

"No Problem!" - If it works in DC, it'll work in DCC! In fact, your new AR unit will simply replace the switch you currently use - You've already got the wiring "debugged" and in place - Simple!

Cheers,
Ian

 

[hamltnblue]

Those turnouts look like they are going to be an issue since you only have one set of insulated joiners.

 

[jtomai]

But the loop in my layout runs thru 2 Main Lines

Im unware if you studied the sketch, but the loop isn't as simple as the one the show in the instructions for the Digitrax AR1 Auto Reverser. They show a simple track heading out and circling back on into itself. Figure that looping section is 8 feet, etc...

Mine here is TWO separate main line ovals connected via a "indirect" loop which begins at the point where I have the "!" exclamation point on the sketch, and is completed at the first branching turnout where the train pases thru line #2, then turns into line #1. So, the reversing "section" of track -as required to be identified, because while the train is using the reversing loop, this section will change polarity- is Infinitely huge as my plan is not to scale. Everything on the plan to the left of the switching areas there is like 75 feet of track wrapping around the room.

I cant seem to identify the "looping setion" to be isolated. If my thinking is correct, its HUGE.

 

[fast_ian]

Im unware if you studied the sketch, but the loop isn't as simple as the one the show in the instructions for the Digitrax AR1 Auto Reverser. They show a simple track heading out and circling back on into itself. Figure that looping section is 8 feet, etc...

"Illustrative purposes only....." The reversed loop could be a whole other railroad.

I cant seem to identify the "looping setion" to be isolated. If my thinking is correct, its HUGE.

No problem! You *must* already have it as an isolated block (somewhere else there has to be another pair of insulating rail joiners or nothing would work!) - Doesn't matter how big the "loop" is, but it's gotta be isolated from the rest already - Power the main track directly and the reversing loop via an AR1 (or whatever) and you're done.

Cheers,
Ian

 

[picsntrains]

I think it was said but you need two insulating gaps.

The best way is to install an automatic reverser on the isolated section.

This won't work for the layout given, but if it was just a single balloon track, not connected to anything else, then there is another way. I haven't actually done it but if you controlled the turnout with an automated board like a ServoPoint that has a built-in relay, you could use the relay to control the polarity of the balloon track so it matches the direction of the turnout. Since you always want to hit the turnout when it is in the correct direction, your polarity should always be correct.

Probably more than most people want and it limits the usefulness of the balloon track.

I use automatic reversers of my own design.

I'm facing a reversing issue right now on my main line. I have two parallel tracks running around the rec room. I have crossovers with gaps that cause a short when the loco goes from the southbound track to the northbound track. I think I will rewire it so there is no polarity conflict but then I'll need to install reversers on both ends of the main line, on the balloons.

Chuck

 

[cv_acr]

(please see Diagram)
Will DCC magically solve the polarity issue with the reverse loop?

Absolutely not. The plan as shown does not have any isolated reversing section at all. Only a single gap to prevent the dead short from happening. Whether we're talking DC polarity or AC phase, the result is exactly the same - a short circuit and it has to be handled the same way. The nice thing about DCC is you can optionally use an electronic auto-reverser instead of a toggle switch to automatically change the phase.

In order to be able to completely reverse a train, you need to have a fully isolated section of track, long enough to contain a train (metals wheels on cars bridging the gap will also cause a short) but also guaranteed to not include more than one train. The method of identifying and isolating this does not change whether you are using DC or DCC.

Also, will DCC simply use my existing (+) & (-) feeders & bus lines?

Yes it can.



See attached image; your original plan with a few notes. Note that with DCC, those three gaps are all you need. Using conventional DC, you will need several more in order to break the layout up into control blocks so that you can actually independently run two trains. The nice thing about DCC is you don't even have to think about that part.