DCC Reverse loop section on the mainline

[rgeiter]

Does anyone have a reverse loop section of track on their mainline?

Let me explain.

On my mainline, which is single track, loops back and passes itself in the opposite direction. I put a crossover in from one track to the other, thus creating a reverse loop. What I was thinking of doing was to isolate one turnout and about two feet of track on either side of that turnout and make that the reverse loop section. I’ll be using a Digitrax booster for that section since I have plenty.

Will that work? I’ve always had a reverse loop section on one leg of a wye, never on the main. What say you.

Thanks,Bob

 

[bnsf971]

If at all possible, I'd want it in the leg of the wye. If it's something you're only going to use occasionally, it'll probably work out. If it's going to be something you're going to use every time a train rolls through, it may develop issues, just from constantly switching "polarity".

 

[rgeiter]

If at all possible, I'd want it in the leg of the wye. If it's something you're only going to use occasionally, it'll probably work out. If it's going to be something you're going to use every time a train rolls through, it may develop issues, just from constantly switching "polarity".

Yeah, every train will pass over it. Don’t know any other way to avoid it. There will actually be two of them on the main.

 

[rgeiter]

If at all possible, I'd want it in the leg of the wye. If it's something you're only going to use occasionally, it'll probably work out. If it's going to be something you're going to use every time a train rolls through, it may develop issues, just from constantly switching "polarity".

Here you can see one of them.

 

[insomniville]

If it's going to be something you're going to use every time a train rolls through, it may develop issues, just from constantly switching "polarity".

Can you clarify why that would be? I get the concept of a reverse loop, but I don't know anything about how reverse loops are implemented circuit-wise or why they would be problematic.

 

[bnsf971]

Can you clarify why that would be? I get the concept of a reverse loop, but I don't know anything about how reverse loops are implemented circuit-wise or why they would be problematic.

Since it's DCC, it's both simpler and more complex than if it were straight DC. The electronics will have to sense the short, then change the signal to match what the lead engine is using. Then it will need to sense and switch back. If there are multiple engines involved, every engine will put the reversing circuit through this process--every time a train passes through the reverse circuit.
I, and many other modelers, try to avoid them as much as possible, if for no other reason than "if it's not there, it can't break".

 

[ctclibby]

Does anyone have a reverse loop section of track on their mainline?

Let me explain.

On my mainline, which is single track, loops back and passes itself in the opposite direction. I put a crossover in from one track to the other, thus creating a reverse loop. What I was thinking of doing was to isolate one turnout and about two feet of track on either side of that turnout and make that the reverse loop section. I’ll be using a Digitrax booster for that section since I have plenty.

Will that work? I’ve always had a reverse loop section on one leg of a wye, never on the main. What say you.

Thanks,Bob

Bob: I will take a stab at this. The actual reversing section is between the crossover turnouts which makes things complicated. I have always thought that reversing sections need to be the length of your longest train. That may or may not be true, others can chime in on this.

Don't think there is an easy way to do this; maybe a train length before the loop, do 2 tracks into 3. The center track is now a reversing section. Yes, your loop will end up being double track. Need to add a wye switch to the center track for handling the return loop, which also needs an additional reverser. Can-o-worms but could work.

L8r

 

[timlange3]

Does anyone have a reverse loop section of track on their mainline?

Let me explain.

On my mainline, which is single track, loops back and passes itself in the opposite direction. I put a crossover in from one track to the other, thus creating a reverse loop. What I was thinking of doing was to isolate one turnout and about two feet of track on either side of that turnout and make that the reverse loop section. I’ll be using a Digitrax booster for that section since I have plenty.

Will that work? I’ve always had a reverse loop section on one leg of a wye, never on the main. What say you.

Thanks,Bob

Bob, you should isolate the loop, not the crossover or turnouts. The loop should be long enough to hold a complete train, or at least all the locos and cars that draw power. Then use an AR-1 or booster to sense and flip polarity of the loop as needed. To completely automate this you can make sections of the loop track adjacent to the turnout(s) isolated and install block / presence sensing electronics that can control a turnout. I believe Digitrax has the equipment to do this with one piece of electronics (plus the electronics to throw the turnout).

 

[ctclibby]

Bob, you should isolate the loop, not the crossover or turnouts. The loop should be long enough to hold a complete train, or at least all the locos and cars that draw power. Then use an AR-1 or booster to sense and flip polarity of the loop as needed. To completely automate this you can make sections of the loop track adjacent to the turnout(s) isolated and install block / presence sensing electronics that can control a turnout. I believe Digitrax has the equipment to do this with one piece of electronics (plus the electronics to throw the turnout).

Tim: Not sure that is correct. I see the crossover as the actual reversing loop. Draw a quick plan and zoom in enough to see both rails ( if needed ) and follow one rail with your finger. Using the crossover, if you get back to the other rail where you started, reversing section. Don't think isolating the loop does anything. The loop is the main line coming back as double track main. If no crossover nothing is needed to handle and train length is moot. If single crossover, the loop has to handle a complete train, else it would run into itself if going back to the main track it came from. Either single/double crossover there is not enough room between the turnouts for a complete train and would probably drive an AR nuts, releasing its smoke.

L8r

 

[timlange3]

Tim: Not sure that is correct. I see the crossover as the actual reversing loop. Draw a quick plan and zoom in enough to see both rails ( if needed ) and follow one rail with your finger. Using the crossover, if you get back to the other rail where you started, reversing section. Don't think isolating the loop does anything. The loop is the main line coming back as double track main. If no crossover nothing is needed to handle and train length is moot. If single crossover, the loop has to handle a complete train, else it would run into itself if going back to the main track it came from. Either single/double crossover there is not enough room between the turnouts for a complete train and would probably drive an AR nuts, releasing its smoke.

L8r

I'm just going by the description given. A track diagram would be most helpful.

 

[rgeiter]

I'm just going by the description given. A track diagram would be most helpful.

The two tracks you see in this pic are the same line. It goes away from the crossover and returns. It’s a single track. The crossover I added will cause a short when a loco crosses over. I will need to isolate one of the turnouts and about two feet on of track. That will be my reversing loop section. It will be on the main (which is both tracks). My original question was asking about having a reversing loop on the main. It will be powered and controlled by a booster. I’ve wired many, many reversing loops, just not one that was on a main track.

 

[bnsf971]

The two tracks you see in this pic are the same line. It goes away from the crossover and returns. It’s a single track. The crossover I added will cause a short when a loco crosses over. I will need to isolate one of the turnouts and about two feet on of track. That will be my reversing loop section. It will be on the main (which is both tracks). My original question was asking about having a reversing loop on the main. It will be powered and controlled by a booster. I’ve wired many, many reversing loops, just not one that was on a main track. View attachment 233614

I've let you know my objections. There's nothing "bad" about the idea, an AR-1 should work. But if you go that route, get a spare reversing module. Not being smart, I just know how much Murphy loves electronics.

 

[kjd]

The two tracks you see in this pic are the same line. It goes away from the crossover and returns. It’s a single track. The crossover I added will cause a short when a loco crosses over. I will need to isolate one of the turnouts and about two feet on of track. That will be my reversing loop section. It will be on the main (which is both tracks). My original question was asking about having a reversing loop on the main. It will be powered and controlled by a booster. I’ve wired many, many reversing loops, just not one that was on a main track. View attachment 233614

If the shown track is half a dogbone and is not connected to anything else beyond the crossover, make all the track beyond the crossover the reversed section. It could even be controlled with a power routing switch machine, Tortoise for example. If the route is straight, power is sent one way, if route crosses over, it's sent reversed. The crossover doesn't need to be reversed, just all the track beyond it.

If however, the track in the bottom of the photo is the other half of the dogbone (a train can leave the photo on one track and return in the opposite direction on the other), it will make a short since the crossover would still complete a reverse loop. If that is the case, put insulating joints the far side of the left switch, between the switches and the near side of the right switch, basically include half the crossover in your reverse loop. Since DCC can be switched under the train, that should take care of any scenario I can see, assuming your track plan is a long dogbone shape with a crossover in the middle. The polarity could still be switched with the extra contacts on a switch machine since polarity needs to be one way running straight and the other for crossing over.

Your original question about a reverse section on the main, it is the same as a reverse section anywhere else. The reversed section should be long enough that only one end can be used at a time since the reverser can only match polarity at one joint at a time. Todd's point about making the whole loop the reverse section is a good one. You wouldn't be able to use the crossover unless the other track is clear so it's impossible to have a train too long go through the loop.

 

[rgeiter]

Ok, I think I’ll put this discussion to bed. This is what I decided to do after thinking about it.

Reference the picture below

The turnout on the right and about two feet in front of it and two feet behind it will be isolated. This will be my “reversing loop section”. It will be fed with its own power supply and booster with the booster configured as a reverse loop. This booster will be connected through loco net. I’m pretty sure that the only time the booster will have to “work” is when a train is crossing over from one track to the other. Otherwise, the booster will operate as any other booster powering the main. The trains would just see it as a short power district, about 5 feet long. This layout will have at least 4 power districts on the main, this one will technically be the fifth. I’m pretty sure it won’t have to constantly change the polarity every time a train passes through it. ONLY when a train crosses over from one track to the other.

Thanks for the input.

 

[kjd]

Two feet on either side will work fine with trains less than 2 feet long.

Best practice says the reversing section should be longer than the trains using it since the reverser can only match polarity on one end at a time.

 

[ctclibby]

Ok, I think I’ll put this discussion to bed. This is what I decided to do after thinking about it.

Reference the picture below

The turnout on the right and about two feet in front of it and two feet behind it will be isolated. This will be my “reversing loop section”. It will be fed with its own power supply and booster with the booster configured as a reverse loop. This booster will be connected through loco net. I’m pretty sure that the only time the booster will have to “work” is when a train is crossing over from one track to the other. Otherwise, the booster will operate as any other booster powering the main. The trains would just see it as a short power district, about 5 feet long. This layout will have at least 4 power districts on the main, this one will technically be the fifth. I’m pretty sure it won’t have to constantly change the polarity every time a train passes through it. ONLY when a train crosses over from one track to the other.

Thanks for the input.View attachment 233677

Bob: I think I see what you are attempting. Digitrax DB210/DB220 specification for the reversing part:

That last paragraph's 1st and last sentence are the notable ones. I believe you need both turnouts in the reversing section with suitable point end approaches and that whole section needs to be longer than your longest train length. So, how does the reversing booster know when to operate? Think that the crossover turnout controllers can use separate contacts ( points ) to determine. If route is normal, the reversing booster is not 'switched' in and track power comes from your normal power booster. When route is reversed, track power is 'switched' to the reversing booster. There is no way you can magically say both sets of points will switch at exactly the same time - means no engine power on the approach rails while setting up for the crossover. I would think that an AR1 might be a better way to go: $30 vs over $100 for DB210/220. I think you said the other end of the dog bone will have the same setup. What if you decide to put in crossovers in the middle somewhere? Yes, I realize you have some extra boosters, but.

Isn't RR electronics fun?

L8r

 

[rgeiter]

Two feet on either side will work fine with trains less than 2 feet long.

Best practice says the reversing section should be longer than the trains using it since the reverser can only match polarity on one end at a time.

It just needs enough track for the engines, not the whole train. My freight cars are not powered.

 

[ctclibby]

Going to run lit passenger cars, EoT or even a pusher? I would not limit myself as sooner or later it would probably happen.

 

[rgeiter]

No lit passenger cars, no EOT’s and no pushers/helpers. I’m good there.

 

[kjd]

And no metal wheels? If you do have metal wheels, ensure the gap is sufficient it can't be bridged by the wheels when they cross to the reversed section.

I noticed you have another crossover, does that one work yet? It is the same situation except the loop is farther away.

Edit: I'm still trying to understand the big picture, if you will have the same arrangement at the other end of your layout, a loop connecting the two parallel tracks, I would treat the layout as a double main and put a reverser on each loop. That way, trains can use all the crossovers at will and the only polarity conflicts will be at the ends. Two reversers, one for each end loop, will take care of the entire layout instead of one for each crossover.