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Reverse Loop Control with DC Power

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Reverse Loop Control with DC Power
Posted by SeeYou190 on Wednesday, March 31, 2021 3:28 PM

Dave K
What is the process to reveres the polarity as the train leaves the main line, enters thr turnback and leaves turnback back on to main line?

I am starting a new thread for Dave because there was too much "noise" on the old one.

I think I have compiled the four most practical options for controlling a train on a DC layout as it moves through a reverse loop.

Additional options, clarifications, and actual applications are appreciated. I will update this first post to reflect additional, updated, and corrected information.

The problem with including a reverse loop on DC layouts is that there is a dead short created when the loop is completed. The conductive rails will connect both sides of the power pack output to the rails.

It is neccessary to gap both rails into the reverse loop and add more controls to the layout to control the train through the reverse loop section, and avoid a short circuit.

There are basically four different strategies for controlling a reverse loop on a layout controlled by a DC power pack.

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Method 1:

This uses the power pack output to the main line, and uses a DPDT reversing switch for the reverse loop polarity.

Operation: The turnout and reverse loop DPDT must be aligned for the incoming train. The train is stopped in the reverse loop section. Then the direction switch on the power pack, polarity switch for the reverse loop, and the turnout direction are all switched.  Then the train can continue on the run.

Advantage: Easy the install.

Disadvatage: Train must stop.

Options: Use a 4PDT toggle to control reverse loop polarity and the switch machine at the same time. It is possible to throw the power pack direction and reverse loop polarity at the same time to avoid stopping the train.

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Method 2:

This uses two seperate DPDT toggles to reverse polarity on main line and reverse loop without using the power pack direction switch.

Operation: The reverse loop polarity, mainline polarity and turnout must all be aligned before the train enters the reverse loop. As the train travels through the loop, the mainline polarity is reversed and the turnout thrown. The train can continue without stopping.

Advantage: The train does not need to stop.

Disadvantages: The position of three different reversing switches can become very confusing. This is an inconvenient operation if using walkaround DC throttles.

Option: This method can be wired using Atas Twin for simple installation.

-     -     -     -     -     -     -     -     -     -     -     -     -     -

Method 3:

This uses a bridge rectifier and no additional polarity switches.

Operation: as the train approaches the turnout is aligned so the train can enter the reverse loop. While the train passes through the reverse loop, the turnout direction is changed and the direction switch on the power pack is reversed.

Advantages: Very simple operation. No need to stop the train in the reverse loop section.

Disadvantages: Train can only pass one direction through the loop. The train will slow down while in the loop due to voltage drop through the diodes in bridge rectifier.

-     -     -     -     -     -     -     -     -     -     -     -     -     -

Method 4:

This adds a directional DPDT polarity switch to the bridge rectifier outpur used in the previous method.

Operation: As the train approaches, the turnout and polarity of the reverse loop switch are set to match. As the train passes through the reverse the loop, the turnout is thrown and the direction switch on the power pack is reversed.

Advantages: Simple operation. No need to stop the train in the reverse loop section.

Disadvantage: The train will slow down while in the loop due to voltage drop through the diodes in bridge rectifier.

-     -     -     -     -     -     -     -     -     -     -     -     -     -

Reverse Loop Operation on the planned STRATTON AND GILLETTE:

For the sixth version of the SGRR I have come up with this operating scheme... There are basically three semi-independent operating "loops". I have left out the two mainline loops from the sketch to declutter the image.

The sketch shows a simplified version of the "meat and potatoes" operations of the layout I call the "local" loop. This loop is where 90% of the switching activity will take place, and where I plan to get most of my operational enjoyment.

The local loop connects four cities, Centerville, Port Annabel, Machester, and Great Divide. Manchester and Great Divide are represented by shared hidden staging tracks. The other two loops just represent the North/South mainline operations through Centerville. The local loop also contains the only reverse loop section on the layout.

 As trains travel in between Port Annabel and the hidden staging tracks that represent "Great Divide", they will traverse the reversing section of the loop. The power pack supply for this section of track will be polarity controlled by a reversing DPDT switch as described in Method #1 above.

There are two tracks in the reverse section. One of these will be a trailing-point siding for each direction of travel. Trains traveling into staging will switch a car at the small industry, and trains coming put of staging will switch cars at the interchange track.

These switching operations will require the train to reverse direction to switch these tracks. For this operation, the first change of direction for the train will be made with the DPDT polarite switch for the reverse loop. All subsequent changes of dirction will be done with the reversing switch on the hand held DC controller.

This set up will be very simple to install, and almost completely invisible for train operations. I am confident this is the best choice for reverse loop operations on the planned layout.

I hope this helps.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by doctorwayne on Wednesday, March 31, 2021 5:52 PM

My original 4'x8' layout had two reverse loops, one within the main oval, and one which could be switched to track outside the oval, which was then elevated and crossed the oval on a truss bridge and a wooden trestle, then returned to the other side of the oval, at ground-level.

Each reversing loop was electrically-isolated (both rails) from the rest of the layout, and there was a double throw switch which controlled direction within both of those loops, as only one would be in use at any time. 

Before the train entered either loop, the direction switch for the loop needed to be aligned for the proper direction.  While the loco was within the isolated loop, another switch, which controlled direction for the rest of the layout, would be re-positioned to allow the train to continue without need of stopping.

Here's a rough sketch done from memory (click on photo to enlarge)...

The layout, built by my father, was Atlas brass flextrack on fibre ties, with all but one turnout also Atlas, buit from kits.  The non-Atlas turnout was a scratchbuilt #8, again done by my father.
All turnouts were remotely controlled by use of choke wires, which rotated an under-table mechanism to move the points (I wish that I had taken photos of that mechanism, as it was very easy to use, and included rotating targets on the switchstands.
All locos and rolling stock had Kadee K-type couplers, and there were multiple uncoupling ramps, also remotely activated from the control panel. 

Wayne

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Posted by SeeYou190 on Wednesday, March 31, 2021 6:30 PM

The thread got moved to "Electronics and DCC".

OK.

Edited to correct the colour coding of the bridge rectifier in Method #4.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by mbinsewi on Wednesday, March 31, 2021 8:30 PM

In the late 80's, I built this:

The "Y" needed a reversing switch, so I used the Atlas #220:

Mike.

 

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Posted by RR_Mel on Wednesday, March 31, 2021 9:31 PM

I started out in HO in 1951 as a 14yr old.  I pretty much self taught myself how to wire my layout.  I used blocks back then and still do.  All blocks have a DPDT center off toggle switch with a home run from the track to the switch.

When I started my current layout in 1989 I went with block control, I guess after using block control for 38 years I was comfortable with throwing switches.

When I cutover to dual mode DC or DCC I made an attempt at following the DCC Guru way but it dinged all my signaling so I rewired it back to original DC block control.  The DCC operation works as well as the DC block operation.

I purchased an MRC Prodigy Advance² DCC System, I had used MRC power DC packs for 50 years without a single problem.

The DCC system has worked perfect on my block wiring since day one.

All that to get around to saying if it was my layout I would go with the DPDT toggles, simplest way, KISS!


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



My Model Railroad    
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Posted by SeeYou190 on Wednesday, March 31, 2021 9:33 PM

Mike:

Can you help me understand the Atlas 220 switch. My understanding is that it is a DPDT selector switch to select one of two cabs (green switch), and then another DPDT switch as a polarity reverser for the reverse loop section (white switch).

Is this accurate?

What are the red switches for? Why are there three output terminals?

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by SeeYou190 on Wednesday, March 31, 2021 9:35 PM

Edited first post to include using the Atlas Twin as an option for method number 2.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by Lastspikemike on Wednesday, March 31, 2021 9:56 PM

Not the Mike you mean but the 220 is quite clever. Atlas has a schematic in the wiring book if you're interested. 

There are three reversing switches. Two red and one grey.  The red ones are basically the twin switch (one red switch and the grey switch form a twin switch) and replace the powerpack's reversing switches. The powerpack reversing switches are left in forwards (or reverse if you want to get confused) and not used at all. The grey button only reverses polarity in the reversing loop/wye/turntable  circuit. 

The 220 is designed for common rail.

The tricky part about the 220 is the Atlas instructions are a tad vague. If you look at the figures in the wiring book or the diagram on the back of the package you'll wire it incorrectly.  If you examine the schematic you'll see right away that the instruction diagram is incorrect.

The common rail polarity feeds the top and bottom left side terminals and connects to the track through the left terminal of the three top side terminals that power the reversing loop. That common terminal feeds the common rail for the layout. The figures and the packaging seem to indicate  that the powerpacks are wired to the four left side terminals + - + - but actually it is + - - +.   

The inner two terminals on the left side feed the block power polarity. Those flow through to the outermost terminals on the exit side (right side) of the 220 which power the block sections in a common rail system. Because they line up it looks like those should flow through from the common rail inputs but they do not.

The green button selects the two cabs and connects the selected cab to the reversing loop.  It's like a block selector switch. 

Alyth Yard

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Posted by Dave K on Thursday, April 1, 2021 7:22 AM

Kevin,

 

Great article.  I will keep it simple but ultimately move to some form of automation.

 

Dave K.

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Posted by Lastspikemike on Thursday, April 1, 2021 8:23 AM

SeeYou190

Edited first post to include using the Atlas Twin as an option for method number 2.

-Kevin

 

The Atlas twin just replaces the powerpack reversing switch providing separate polarity control to each circuit. Without the separate polarity control for both circuits you have to stop the train. Not sure why anyone would want to wire it that way.

Since you never use the powerpack reversing switch the Twin Switch wiring is no more confusing than Option 1. A Twin Switch is just two DPDT in one package. Handy, if they aren't defective!!

To add to Option 2 the turnout controlled polarity switching capability described as an option to Option 1 you need only provide main line powered track sections between the turnout and the reversing loop gaps long enough to accommodate your locomotive consist. Then you reverse polarity of the main as the train fully enters the reversing loop and throw the turnout to the exit lining only when the locomotive consist leaves the reversing loop but before reaching the turnout. This shortens the reversing loop.

We have found that with the MRC 780 at least you can cheat on train length and the very brief shorting caused by metal wheels on trailing cars crossing gaps does not throw the breaker. Haven't checked the rails or rolling stock wheels for pitting.

 This will not work for DCC because decoders can react to very brief shorts but in that case we will wire those short main line sections to be separately switchable  to align with booster phase correct and use switchable Ito reverse units for our three reversing loops. These have to be switchable because DC power and autoreversers are incompatible.

Alyth Yard

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Posted by mbinsewi on Thursday, April 1, 2021 8:31 AM

SeeYou190
Can you help me understand the Atlas 220 switch.

Here's an instruction pdf from Atlas.

http://download.atlasrr.com/pdf/Item220Instructions.pdf

To keep the flow of the train smooth, I remember I had to be watching, and ready at the switch.  Nothing was automatic like todays DCC auto reverse controlers are.

Mike.

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Posted by Lastspikemike on Thursday, April 1, 2021 8:45 AM

Yes, that's the diagram that is incorrect.

You'll note it appears as though the two cabs are wired to the four left side 220 terminals in the same relative order: + - + -  . If you do that the 220 will be short circuited internally. You can ask me how I know this and how long it took for us to figure it out. Thanks Atlas.

If you look at the schematic wiring instead of the figure you will see immediately that the four left side terminals are + - - +.  The schematic unfortunately orients the red main reversing switches as if they are up/down when they are actually left/right.

The easiest way to see this is to trace the C or Common rail track terminal (left most of the three terminals across the top edge) back to each Cab's reversing switch on the 220. You must not try to use the actual powerpack reversing switch, nor indeed any reversing switch in a gang of more than one 220 except for the one closest to the track power connections.

The clever part about the 220 is the way it powers the reversing loop separately from the main but uses just the one Common rail terminal to do so.  

If you gang more than one 220 you must not use the reversing switches nor the C terminal in any of the gang except for the last one in the chain or the 220 will not flow current. The powerpack reversing switch is never used if you have a 220.

Note the return wiring from the block rails connects to the outermost terminals on the right side of the 220. Trace the internal wiring and you'll see those cross over to the "inside"  terminal of each pair of Cab power wires on the left side of the 220. Note also that when you gang a Selector (215) to the right side of the last 220 there's no connection of the inner two right side terminals between the 220 and the 215.

Atlas finally realized those were redundant power sources for the Common rail. Latest version of the 220 do not even have those right side power exit C connection across the gang terminals.

We have a gang of three 220 connected to a gang of 4  215. Two of the 215 are connected as a sub block with a Cab C powering one set of circuits. Cabs A and B can feed all 16 blocks while Cab C only powers 8 blocks.

One nifty aspect of the 220 is that the polarity switches are oriented left/right and the Cab selector is oriented up/down just as powerpacks and Selector switches are oriented. We have three reversing loops each controlled by a ganged 220. Two of the loops are facing loops created by two crossovers inserted into a dogbone loop, creating an X track. The X track is wired as main (red switch on the 220) and each reversing loop gets its own grey switch. We wired it all so that when the three switches (one red and two grey) are aligned in the same direction then the loops are powered for continuous running. Whenever one switch is not aligned then we know the train currently running the loops is going to use a crossover or it will short out. Once the crossover is negotiated and the train enters the loop in reverse direction the other two switches are aligned to match again. 

Not confusing at all. 

Alyth Yard

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Posted by SeeYou190 on Thursday, April 1, 2021 9:11 AM

mbinsewi
Here's an instruction pdf from Atlas.

Thank Mike. I also found a pretty good description online outlining the sequence of operation when using the Atlas 220 on a layout.

Since the Atlas 220 is so similar to method number 2 in my diagrams, and also since all my examples are pretty simple showing only one cab, my gut feeling is to leave the Atlas 220 out of the list of examples.

Does this sound right to you?

Or, should I add a method 5 with the Atlas 220, or maybe add another note about the product to the text for description 2?

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by Lastspikemike on Thursday, April 1, 2021 9:21 AM

The 220 is identical to Option 2 as you describe it. The only difference is it conveniently adds two Cab capability to Option 2 but adding only one additional DPDT switch. 

You can use a 220 as a Twin Switch with only one Cab if you like. 

The last two 220 I bought were defective from new.

At least two more we have installed are defective in at least one reversing switch.

Just so you know.

Atlas now has a serious QA problem on its hands, perhaps not coincidentally connected to their production move  to China. The quality of the casting of their plastic cases is critical to the reliability of the operation of the plastic switches. The circuit boards themselves are not likely the problem. The "center off" capability of their plastic switches seems to be the problem area.

Alyth Yard

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Posted by SeeYou190 on Thursday, April 1, 2021 10:12 AM

Edited first post to correct two spelling errors.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by mbinsewi on Thursday, April 1, 2021 11:13 AM

It's up to you Kevin.  I had the 220 hooked up to 3 #215 selectors, and used common rail, with 2 cabs.

I installed it as per Atlas instructions, and had no problems.  I think the instructions were on the back of the package, plus I had a book by, I think, Linn Wescott, describing and showing examples of wiring methods, use toggles, and a section on setting up Atlas components.

Mike.

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Posted by SeeYou190 on Thursday, April 1, 2021 11:35 AM

mbinsewi
It's up to you Kevin.  I had the 220 hooked up to 3 #215 selectors, and used common rail, with 2 cabs.

I think I will leave it out because the scope of this thread is just different ways to "skin the cat" for DC reverse loops, and I don't want to over complicate it with multiple cabs.

I appreciate the input Mike. Thank you.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by mbinsewi on Thursday, April 1, 2021 12:05 PM

Actually, I had to go look for the book.  It's called "HO Primer, Model Railroading for All", by Linn Westcott.

His perferred method is the 2 toggles, like what you show, and using the Atlas Twin #210.

Mike.

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Posted by SeeYou190 on Thursday, April 1, 2021 12:20 PM

mbinsewi
Actually, I had to go look for the book.  It's called "HO Primer, Model Railroading for All", by Linn Westcott.

The HO Primer was a great book. I wish Kalmbach Media would update it and do a new printing.

I think it was a great vehicle to get newcomers into model railroading.

-Keivn

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by SeeYou190 on Thursday, April 1, 2021 12:21 PM

Edited first post to include an explanation of reverse loop short circuits and an additional illustration.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by SeeYou190 on Thursday, April 1, 2021 12:51 PM

Dave K
Great article.  I will keep it simple but ultimately move to some form of automation.

I am so glad you are finding this useful.

I have no experience with automating the operation of a reverse loop, so I cannot offer any assistance with that task.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by SeeYou190 on Friday, April 2, 2021 9:33 AM

Edited first post to include a description of reverse loop integration, control, and operation on the STRATTON AND GILLETTE railroad.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by Dave K on Tuesday, April 6, 2021 7:06 AM
I have attached pictures of my two DPDT switch arrangement for the 1st turn back polarity reversal.  Switch on left controls mainline while the one on the right controls the turn back section polarity.  I've attached pictures of the mainline feeders, turn back section feeders and the switch setup.  I've wired the switches in an X formation to control polarity.  What is strange is the left switch has power when switch is in the center and up position but shorts in the down position.  the right switch has no power in the center off but has power at up but also shorts in the down position.  Is there something wrong with the cross wiring?  I've checked for touching wires but cannot figure it out.
 Dave

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Posted by mbinsewi on Tuesday, April 6, 2021 8:06 AM

Your picture is not working.

Mike.

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Posted by Lastspikemike on Tuesday, April 6, 2021 8:20 AM

The usual connection pattern is track power out from each set of the two center terminals and powerpack power in to the two terminals  at one end of each DPDT with diagonal connections across the ends. 

Its all relative so you can wire it up for current to flow in the other direction through the switches. The power can go into or flow out of the center terminals. 

It also doesn't matter which end of the knife switch style is wired to in or out, as the case may be, the polarity reversal occurs through the diagonal connections.

https://m.youtube.com/watch?v=u0Lm3P1U7UQ

 

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Posted by Dave K on Tuesday, April 6, 2021 8:21 AM
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Posted by SeeYou190 on Tuesday, April 6, 2021 8:32 AM

Dave,

I am still editing the original post for clarity and accuracy.

Since you are the "target audience" for this thread...

Was it helpful?

Should anything be changed?

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by Lastspikemike on Tuesday, April 6, 2021 8:36 AM

I only see the one set of isolating joiners at one point, which tipped me off to the possibility you have a more complex problem than you think you do. You need two sets within each reversing loop. Also, we assumed that you have only the one reversing section. Is it possible your "main" is also a reversing section somehow?

Looking again at your photos in the first thread and the detail photos in  this thread I now see three reversing loops, two of which interlock with each other along a common section of track.

http://cs.trains.com/mrr/f/744/t/287124.aspx?page=1

 

One loop has an overpass and is easily identified but I see a second loop interlocked with that overpass looop, 2/3 of a reversing Wye in fact. That may be tricky to isolate since one leg of each reversing loop is in fact common to both. That's quite tricky to wire. You may need to treat those two reversing loops as a  separate layout for wiring purposes with the "main line" being that common section of track. Have a look at the isolation and connections needed for a Wye.

http://cs.trains.com/mrr/f/744/p/256393/2870622.aspx

 

The third reversing loop appears to be outside those two crossover loops but inside your main line.  The photo taken from one end obscures the view of the double track at the far end and its connection back to main on the right side of the photo but it seems you need two more DPDT and another two sets of isolating joiners in that outside loop. If you could post a photo taken from a higher viewpoint, showing the whole track alignment we could identify the second loop for you, assuming my deduction is correct. I see third pair of isolating joiners quite a long way from the first two pairs. That's a tip off to me that you also need another pair of isolating joiners and a third DPDT. I can't tell from the limited views in the photos.

Power from one DPDT feeds only the two rails inside the isolated reversing loop section,  the other DPDT feeds both rails of the rest of your layout, assuming you don't have another reversing section lurking somewhere in your main line, and you appear to have three. 

Your DPDT switches seem wired correctly although without knowing which terminals receive power and which deliver to the track it is hard to know just from pictures. I do not think you have isolating joiners in all the necessary places. 

I advise you to draw yourself a schematic of your actual wiring and compare that to this: 

https://forum.digikey.com/t/polarity-reversal-using-a-dpdt-switch/626

Or scroll up to the Method 2 diagram above, which is what you're trying to achieve. You have three loops to wire though. 

Or, break out a circuit tester or multi meter and check the circuit connections that way.

A sketch of your layout would help a lot to resolve your polarity problems.

I mention that you might have wired the Twin switches incorrectly in the same way. Sounds like you have arrived at the same place electrically speaking. 

Alyth Yard

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Posted by SeeYou190 on Tuesday, April 6, 2021 10:27 AM

Dave,

I read the email you sent me and looked at the pictures.

I believe you need to cut (or install) another pair of rail gaps/insulated joiners on the reversing section.

When the switch is up, polarity matches the mainline... OK.

When the switch is off, the reversing section is feeding power from the mainline... not OK.

When the switch is down, polarity mismatch, short circuit... Failure.

Please let me know if this is getting you in the right direction.

-Kevin

Wink Happily modeling my STRATTON & GILLETTE RAILROAD. A Class A line located in a personal fantasy world of semi-plausible nonsense on Tuesday, August 3rd, 1954.

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Posted by richhotrain on Tuesday, April 6, 2021 10:41 AM

Interesting and worthwhile thread.

But, I have a one word reaction to DC reverse loops - - ugh!

Thank goodness for DCC.

Rich

Alton Junction

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