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Reversing Loop Wiring

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Reversing Loop Wiring
Posted by Inukshuk on Saturday, June 12, 2021 12:14 PM

I am rebuilding my layout and want to incorporate a reversing loop.  Normally, this would not be a problem, but I would like to turna 10 car passenger train. Because of the length it would extend over the line that connects both sides of the oval. I realize that I would have to isolate part of my mainline to include the length of the train.  I understand the concept in going in one direction, but not sure what I would need to do in going the other direction.

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Posted by BigDaddy on Monday, June 14, 2021 11:55 AM

Welcome to the forum.  Your posts are delayed in moderation for a bit.

This is a case where a visible track plan would be helpful.  Posting pictures in this forum is unique and you have to follow the directions here

Henry

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Posted by CSX Robert on Monday, June 14, 2021 12:49 PM

It sounds like you're talking about a simple oval with a single revering track bisecting it.  What you'll have to do is divide th elayout into at least three blocks, the reversing section and two blocks on the oval, each "half" where it is divided by the reversing track.  That way you can swap the polarity if each half of the oval to match the polarity at the two ends of the reversing track.

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Posted by jjdamnit on Monday, June 14, 2021 2:05 PM

Hello All,

DC or DCC?

This makes a huge difference in how you can switch polarity.

In DC you will need a manual solution while in DCC you can use a manual solution or automate the process.

A track diagram always helps.

In a polarity reversing section only the electronic components need to be isolated in the section.

Unless the cars or caboose have electrical components; lights, axles with resistors for detection circuits, then only the motive power has to be in the section when the polarity shift occurs.

For example: If only the locomotive(s) is/are the only "electrical component" in the train, no matter how many cars being pulled- -even with metal wheels- -the entire length of the train doesn't need to be isolated in the polarity reversing section.

If however, you have a caboose or passenger car(s) with lights or rolling stock with resistors installed on the wheels for block detection, then those components need to be factored into the length of the polarity reversing section.

Keep the questions coming and...

Hope this helps.

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Posted by Lastspikemike on Monday, June 14, 2021 4:34 PM

Inukshuk

I am rebuilding my layout and want to incorporate a reversing loop.  Normally, this would not be a problem, but I would like to turna 10 car passenger train. Because of the length it would extend over the line that connects both sides of the oval. I realize that I would have to isolate part of my mainline to include the length of the train.  I understand the concept in going in one direction, but not sure what I would need to do in going the other direction.

 

What you describe is not a reversing loop but a reversing section. A line crossing from one side of a loop to the other looks like it creates a reversing loop but it really doesn't.  It looks like it creates two "loops" back to back but it really doesn't.

Also, if you build only one such crossing track you can turn a train once but then you can't reverse it back again unless you actually reverse the train back across the connector. You would be better with two crossing tracks. Single crossing tracks will be annoying quite quickly. If you need to you can use a diamond or 90 degree crossing track piece to allow one reversing track to actually physically cross the other in order to squeeze two crossing tracks inside one oval.  You still have to deal with the problem of train length as you obviously can't physically cross part of a train though another part. 

Metal wheels will spark and pit rails and wheels if you have a train longer than the reversing section. This is because you can only match polarity at one end of the reversing section at a time.   You should make sure the entire isolated part of your reversing section is longer than your longest train. The reversing section can include one of the turnouts forming part of the crossing track.

You can make the reversing section as long as you like until you reach the second turnout making up the crossing track itself. Polarity only needs to be changed to match when the train reaches one turnout or the other.

 

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Posted by Lastspikemike on Monday, June 14, 2021 4:41 PM

CSX Robert

It sounds like you're talking about a simple oval with a single revering track bisecting it.  What you'll have to do is divide th elayout into at least three blocks, the reversing section and two blocks on the oval, each "half" where it is divided by the reversing track.  That way you can swap the polarity if each half of the oval to match the polarity at the two ends of the reversing track.

 

The Atlas Wiring book shows a few cases where only two blocks are required. Why do you see three as the minimum?

You can do it with two blocks even if you have two crossing tracks.

Three allows more options for control but technically two blocks are enough. You change polarity in the "other" block while the train is in the so called "reversing section". Actually, both blocks are "reversing sections" in a two block system. 

Atlas uses one Twin switch to control polarity. Two DPDT integrated into one switch.  

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Posted by gregc on Monday, June 14, 2021 4:47 PM

CSX Robert
That way you can swap the polarity if each half of the oval to match the polarity at the two ends of the reversing track.

wouldn't reversing the mainline polarity reverse it in both blocks?

greg - Philadelphia & Reading / Reading

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Posted by RR_Mel on Monday, June 14, 2021 4:59 PM

Here we go again, if everyone would just ignore Laststpikemike maybe he will go away.  He just enjoys mudding up every topic he can.


Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951



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Aging is not for wimps.

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Posted by Lastspikemike on Monday, June 14, 2021 5:05 PM

gregc

 

 
CSX Robert
That way you can swap the polarity if each half of the oval to match the polarity at the two ends of the reversing track.

 

wouldn't reversing the mainline polarity reverse it in both blocks?

 

Two blocks, two DPDT. The powerpack reversing switch is no longer used. Like the Atlas 220 situation discussed on another thread. Atlas Twin switch doesn't depend on common rail, or at least I don't think it does.

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Posted by richhotrain on Monday, June 14, 2021 5:14 PM

Folks, we don't even know if the OP is operating in DC or DCC, and we cannot be sure at this point what his layout even looks like.

Rich

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Posted by MisterBeasley on Monday, June 14, 2021 5:15 PM

We need to know if this will be DC or DCC before we go much further.

I've built these crossovers on ovals, and if I had it to do again, I would extend the insulated sections outward, beyond the turnouts for the reversing section so that parts of the oval would actually be parts of the reversing section.  This lengthens the reversing section.

I have run trains with illuminated cabeese and passenger cars.  I run miy reversing crossover with DCC.  It's a fast, solid state one, and tolerates the rapid changeovers at the end of the train well.

 

 

 

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Posted by Lastspikemike on Monday, June 14, 2021 5:21 PM

richhotrain

Folks, we don't even know if the OP is operating in DC or DCC, and we cannot be sure at this point what his layout even looks like.

Rich

 

Physically the reversing section is constructed the same way for DC or DCC. The only difference is how you reverse the "polarity". 

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Posted by Lastspikemike on Monday, June 14, 2021 5:23 PM

RR_Mel

Here we go again, if everyone would just ignore Laststpikemike maybe he will go away.  He just enjoys mudding up every topic he can.


Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951



My Model Railroad    
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
Aging is not for wimps.

 

Quoting the Atlas Wiring book is not and cannot be muddling things up.

You are free to advocate ignoring my posts but you should refrain from inaccuracy when doing so. 

With all due respect.

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Posted by BigDaddy on Monday, June 14, 2021 5:23 PM

While we are awaiting the PO to pony up a few more details and get through moderation, I had thought that metal wheels would trigger a short across the gap.

JJD has a different opinion.

jjdamnit
-even with metal wheels- -the entire length of the train doesn't need to be isolated in the polarity reversing section.

If he is correct, why isn't there a short in that situation.

Henry

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Posted by Lastspikemike on Monday, June 14, 2021 5:24 PM

MisterBeasley

We need to know if this will be DC or DCC before we go much further.

I've built these crossovers on ovals, and if I had it to do again, I would extend the insulated sections outward, beyond the turnouts for the reversing section so that parts of the oval would actually be parts of the reversing section.  This lengthens the reversing section.

I have run trains with illuminated cabeese and passenger cars.  I run miy reversing crossover with DCC.  It's a fast, solid state one, and tolerates the rapid changeovers at the end of the train well.

 

 

 

 

I do not think you can include both turnouts in one block unless you create three blocks.

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Posted by richhotrain on Monday, June 14, 2021 5:44 PM

Lastspikemike
 
richhotrain

Folks, we don't even know if the OP is operating in DC or DCC, and we cannot be sure at this point what his layout even looks like.

Rich 

Physically the reversing section is constructed the same way for DC or DCC. The only difference is how you reverse the "polarity".  

So, given that difference, we need to know whether he is operating in DC or DCC.

 

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Posted by richhotrain on Monday, June 14, 2021 5:48 PM

BigDaddy

While we are awaiting the PO to pony up a few more details and get through moderation, I had thought that metal wheels would trigger a short across the gap.

JJD has a different opinion. 

jjdamnit
-even with metal wheels- -the entire length of the train doesn't need to be isolated in the polarity reversing section. 

If he is correct, why isn't there a short in that situation. 

Good question. I have four reversing sections on my layout. All of my rolling stock has metal wheels.

None are resistored and none of the rolling stock is lighted. Yet, metal wheels on each and every piece of rolling stock are detected by the controlling PSX-AR.

Rich

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Posted by CSX Robert on Monday, June 14, 2021 6:15 PM

Lastspikemike
Why do you see three as the minimum?

That was my initial thought because he specifically stated his train would be longer than the reversing section.  After thinking about it more, he could extend one end of the reversing section out onto the loop, although that could cause issues if he ever wanted to operate a shorter train within the reversing section while also operating one seperately on the loop.

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Posted by Lastspikemike on Monday, June 14, 2021 8:48 PM

richhotrain

 

 
Lastspikemike
 
richhotrain

Folks, we don't even know if the OP is operating in DC or DCC, and we cannot be sure at this point what his layout even looks like.

Rich 

Physically the reversing section is constructed the same way for DC or DCC. The only difference is how you reverse the "polarity".  

 

 

So, given that difference, we need to know whether he is operating in DC or DCC.

 

 

 

Well no because the wiring is also the same. You can manually reverse "polarity" in DCC in the same way  as for DC. The difference is only which switch on the Atlas Twin switch  you throw. For DC it must be the one that controls polarity in the section the train is not in (unless you stop the train and really why would you?) whereas for DCC it doesn't matter.

The OP only asked about train length and whether and how far to extend the reversing section beyond a turnout. The real issue is the OP doesn't seem to yet realize he actually wants two reversing connecting tracks, not just one.

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Posted by Lastspikemike on Monday, June 14, 2021 8:59 PM

CSX Robert

 

 
Lastspikemike
Why do you see three as the minimum?

 

That was my initial thought because he specifically stated his train would be longer than the reversing section.  After thinking about it more, he could extend one end of the reversing section out onto the loop, although that could cause issues if he ever wanted to operate a shorter train within the reversing section while also operating one seperately on the loop.

 

Good point. The third section could be controlled by a selector type block control switch assigning the "extension" piece to either the reversing section or the main loop as required.

It would help to know the dimensions we're dealing with. 

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Posted by Lastspikemike on Monday, June 14, 2021 9:01 PM

BigDaddy

While we are awaiting the PO to pony up a few more details and get through moderation, I had thought that metal wheels would trigger a short across the gap.

JJD has a different opinion.

 

 
jjdamnit
-even with metal wheels- -the entire length of the train doesn't need to be isolated in the polarity reversing section.

 

If he is correct, why isn't there a short in that situation.

 

There is and Atlas warns about this because the sparking can pit wheels and rails.

I know for a fact that the trains will still run fine. The short caused by the wheel tread is so momentary a DC powerpack won't trip. 

For DCC the problem is that momentary short will trip the auto reverser. The locomotive and following cars will then trip it again and again at the other end of the reversing section and so on. You need the whole train to be inside the reversing section so that the auto reverser can reset the phase just once. 

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Posted by Water Level Route on Tuesday, June 15, 2021 6:01 AM

Lastspikemike
The difference is only which switch on the Atlas Twin switch  you throw. For DC it must be the one that controls polarity in the section the train is not in (unless you stop the train and really why would you?) whereas for DCC it doesn't matter.

Except for using the one the train is on causes it to stop as you go past the center off position.  Great suggestion.
Lastspikemike
The real issue is the OP doesn't seem to yet realize he actually wants two reversing connecting tracks, not just one.
You know what others want?  That's quite a feat!

Maybe just sit back and learn something this time.

Mike

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Posted by Lastspikemike on Tuesday, June 15, 2021 8:12 AM

Water Level Route

 

 
Lastspikemike
The difference is only which switch on the Atlas Twin switch  you throw. For DC it must be the one that controls polarity in the section the train is not in (unless you stop the train and really why would you?) whereas for DCC it doesn't matter.

 

Except for using the one the train is on causes it to stop as you go past the center off position.  Great suggestion.

 
Lastspikemike
The real issue is the OP doesn't seem to yet realize he actually wants two reversing connecting tracks, not just one.

You know what others want?  That's quite a feat!

 

Maybe just sit back and learn something this time.

 

Have you tried this? Thought not. Even a DC powered train won't "stop" if you flick the Twin Switch across center off, it reverses immediately. DCC won't even notice the interruption in power. Certainly an onboard keepalive would prevent this from happening. Some decoders from QSI treat the reverse switch as a DCC signal substitute when running in DC mode. The interruption on power is almost indiscernible. 

Nobody can know what another person is thinking, ever. One can know what a person wants even if they do not yet know it themselves. Advertising developers depend on this phenomenon.

Since the OP refers to "the other direction" it seems clear he has not noticed that there is no "other direction" across the reversing section he describes. By considering  the "other direction" he reveals he does want two reversing sections. Also, a crossing track appears to create two reversing sections because two loops are created face to face. You can only reverse the train by going into a turnout and since both turnouts face the same way you're out of luck in one direction. 

I'm always happy to learn and find that sitting back does not facilitate that process. 

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Posted by jjdamnit on Tuesday, June 15, 2021 1:14 PM

Hello All,

jjdamnit
For example: If only the locomotive(s) is/are the only "electrical component" in the train, no matter how many cars being pulled- -even with metal wheels- -the entire length of the train doesn't need to be isolated in the polarity reversing section.

To clarify my response, I am NOT referring to metal wheels crossing the gapped section of track causing the DCC Auto Reversing Unit to trip at each pass of a wheel- -a "micro-short"- -for lack of a better term.

What I am saying is; if a train has metal wheels, and ONLY the motive power is drawing power from the track, crosses into a reverse polarity section, the only "component" (the motive power) needs to be completely in this section.

The rest of the train, with metal wheels, does not need to be entirely in the reversed polarity section. The cars can be half in the reversed polarity section and half in the non-reversed polarity section, as long as the metal wheel(s) are not bridging the gaps in the track. 

In the April, 2021, Model Railroader magazine; pg. 46, in the article "Dealing with reversing sections" there is a graphic of what I am feebly trying to describe in relation to reversing polarity sections and units that draw track power.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by MisterBeasley on Tuesday, June 15, 2021 1:43 PM

If you just have metal wheels, particularly with plastic trucks, and the wheels don't provide power, and you don't stagger your insulation joints, then the contact is momentary and generally not much of a problem.  However, if you're running a string of passenger cars with power from both rails going through both trucks, you have a long period where the auto-reverser needs to keep polarity aligned.  If, at the same time, the engine at the other end of the reversing section also crosses to the main loop, the auto-reverser has an unresolvable conflict that only the 0-5-0 work crane can deal with.

It takes an iron man to play with a toy iron horse. 

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Posted by Lastspikemike on Tuesday, June 15, 2021 2:39 PM

The April 2021 article in MRR does not mention the possible metal wheel effect.

The metal wheel effect will not trigger a DC powerpack short circuit protector. It of course will send a signal to a DCC auto reverser because that's how they work. The idea is the auto reverser  stops getting any wheel shorting signals for long enough that the last phase change it detects aligns the phase for the exit point.

The auto reverser sees the initial short from the lead axle of the train (that could be the first locomotive or the last car if the train backs into the reversing section). That sets the phase for the train to enter and travel through the reversing section. 

As the same lead set of wheels leaves the reversing section the wheel bridges the exit gap and the auto reverser can again reset the phase to match. Only the decoder needs the phases to match. 

The issue is one of probability. Could the lead wheelset trigger a phase change at approximately the same time as a trailing wheelset under a car do the same thing. How lucky are you on a regular basis?

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Posted by CSX Robert on Tuesday, June 15, 2021 3:45 PM

jjdamnit
What I am saying is; if a train has metal wheels, and ONLY the motive power is drawing power from the track, crosses into a reverse polarity section...

jjdamnit
The rest of the train, with metal wheels, does not need to be entirely in the reversed polarity section. The cars can be half in the reversed polarity section and half in the non-reversed polarity section, as long as the metal wheel(s) are not bridging the gaps in the track. 

"Drawing power" is not the critical attribute, it's continuity between the wheels.  If a car is wired for easy installation of track powered lights with the wheels of both trucks wired together, then the entire car has to be either in or out of the reversing section, even if it does not have any lights installed and therefore is not drawing power.  If the car is not wired but the trucks still have continuity between the wheels on each truck, then each entire truck has to be in or out of the reversing section.

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Posted by jjdamnit on Tuesday, June 15, 2021 4:11 PM

Hello All,

RR_Mel
Here we go again, if everyone would just ignore Laststpikemike maybe he will go away.  He just enjoys mudding up every topic he can.

Well, that ain't going to happen so just let him speculate and pontificate.

Lastspikemike
The auto reverser sees the initial short from the lead axle of the train (that could be the first locomotive or the last car if the train backs into the reversing section). That sets the phase for the train to enter and travel through the reversing section.

DCC Auto Reversing Units don't see the short from the axle (paraphrasing).

The ARU detects feedback in the electronic signal or "short" and reacts appropriately. Some ARUs reaction times can be adjusted while some are factory set.

"Reactions" from an ARU can vary from a polarity shift to a complete shut-down of that circuit (track section).

The false premise that insulated metal wheels- -not specifically bridging the gapped track- -will cause the ARU to constantly phase shift in an endless loop (feedback) is not correct.

Lastspikemike
The locomotive and following cars will then trip it again and again at the other end of the reversing section and so on. You need the whole train to be inside the reversing section so that the auto reverser can reset the phase just once.

This opinion predicates that for some reason all wheelsets are electronically "connected".

In reality, unless the frame(s) of the car(s) is/are a conductive material, and the couplers are conductive making the entire train a "live load" then the sixth example on pg. 46; April, 2021, MRM applies.

Hope this helps.

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Posted by jjdamnit on Tuesday, June 15, 2021 4:28 PM

Hello All,

CSX Robert
"Drawing power" is not the critical attribute, it's continuity between the wheels.

Yes, I agree completely!

It's not THE critical attribute.

Any open circuit between the rails needs to be considered as a load or "drawing power" from the tracks or a "load".

That's why one caveat is wheels with resistors installed for block detection purposes.

When these metal wheelsets have been modified they also need to be considered when there is a polarity shift section that cannot accommodate the entire train.

See: Model Railroader Magazine, April 2021; Pg. 46, Fig. 1, Ex. 6.

Hope this helps.

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Posted by CSX Robert on Tuesday, June 15, 2021 6:49 PM

jjdamnit
Any open circuit between the rails needs to be considered as a load or "drawing power" from the tracks or a "load".

That's why one caveat is wheels with resistors installed for block detection purposes.

I don't know what you mean by this, why would an open circuit need to be considered a load?  It's not the load that triggers the autoreverser, it's the short.  And what does that have to do with resistor wheesets, a resistor wheel is a load.

Resisitor wheelsets don't need to be considered any different than regular metal wheels when dealing with an auto reverser.  If they bridge rails of opposite polarity (side to side) they simply put a light load on the track just as they are designed to do.  If the wheel tread bridges the gap and creates a short, that would happen with or without the resistor.

You may get away with running metal wheels on a train that is longer than your reversing section, but best practice is not to.  Even if the wheels are passing over the gap fast enough to not trip the autoreverser, you'll still be getting shorts and micro-arcing as the wheels cross.  That's something best to avoid because it leads to dirtier track and wheels and possible pitting, and could even lead to reduced life of the reverser.

 

Personally, I'm not a fan of autoreversers anyway.  They detect a problem and correct for it, I would much prefer to prevent the problem before hand by matching the track polarity before crossing the gap.

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