# Reversing loop inside a reversing loop



## jwk246 (Apr 9, 2014)

I have a question regarding reversing loops. If I have a reversing loop inside a reversing loop can I get by with one reversing network. My answer to myself after many hours of thinking and drawing of diagrams is yes. If I power the second reversing loop the same as the main line and use the reversing network to only power the first reversing loop, it will work. My reasoning is, when the train is on the main line and enters the first reversing loop the polarity of the reversing loop matches the main line, the reversing network does not sense a short, and therefore does not change the polarity. When the train enters the second reversing loop, which is the same polarity as the main line, the reversing network again senses no short, and does nothing. As the train exits the second reversing loop and enters the first reversing loop the network senses a short and changes the polarity of the first reversing loop. Then as the train goes from the first reversing loop to the main line the network again senses a short and changes the polarity of the first reversing loop to match the main line. Am I right that I need only one reversing loop network?

My question comes about because I have a track plan with an oval around the outside with a folded, twisted, dogbone inside. I can go from the outer oval onto and off the dogbone at four places so that I can leave the dogbone in the same direction I entered or in the reverse direction. I therefore have the entire dogbone powered through a reversing network. Also, inside the dogbone I have a reversing loop and was puzzled on how to keep the polarity proper.


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## rzw0wr (Aug 28, 2013)

If you have a track plan you could post it would help.

From what I am thinking you will need 2 AR units.
I can't see how you can wire the main and a loop the same.


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## DonR (Oct 18, 2012)

Any time there's a question of possible shorting with
a reverse loop you want to consider one track rail red,
the other black. Then finger trace the red rail and
make sure that it never touches a black rail. If it
does, you need isolation and a reverse loop controller, whether it
be stand alone or in connection with another reverse loop.

Another consideration that also is not clear from your
description, the length of each reverse loop. There are
situations if one is too short that there can be shorting on
both ends as metal wheels span the insulated joiners.

As stated, an actual drawing of the layout or a clear
pic showing the situation would be a big help.

Don


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## RT_Coker (Dec 6, 2012)

DonR said:


> There are
> situations if one is too short that there can be shorting on
> both ends as metal wheels span the insulated joiners.


Don,
All my locomotives have multi-wheel-power-pick-up, so I have used clear-finger-nail-polish to extend the rail-gaps so that metal-wheels on the rolling-stock are not a problem. This allows me to run a long train through a shorter reverse-loop. Not recommending this, just providing an alternate way to do things.
Bob


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## jwk246 (Apr 9, 2014)

*reversing loops*

I shouldn't have described my layout. It gets confusing. What I am talking about works for a simple oval layout, I think. If you take any layout with a reversing loop and use a network to look after the polarity of the reversing loop, the network assures the proper polarity when the train enters or leaves the loop, that is, if it senses a short it changes the polarity of the reversing loop. If there is a second reversing loop encountered when the train is still on the first loop the network will do it's thing, that is, change the polarity of the first loop if it senses a short. When the train returns to the first loop from the second loop, the network again senses and changes the first loop polarity, if required -- and so on. There is no need to worry about the polarity of the second loop, the network takes care of it by adjusting the polarity of the first loop. I think.


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## DonR (Oct 18, 2012)

"I think" I follow what you are saying but could not begin
to check it without the actual track layout that you have.
It is intriguing so I hope you'll post it so we can see
what you are saying.

Yes, the theory of a DCC reverse loop controller is to quickly sense 
a mismatch of track phase (polarity) when a loco or lighted car spans
insulated joiners between an isolated section and the main.
It then uses a relay to reverse the isolated track polarity 
so the loco continues on without pause.

Don


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## jwk246 (Apr 9, 2014)

I have a problem - I don't know how to make a layout on my computer and I can't take a picture with my phone. It is a fold-up phone with a camera but I can't get the pictures into the computer. When I get further along on the layout I'll get my son to get a picture and put it on the forum. I also commented several months ago about my layout table - it tilts, so I can do wiring sitting in my chair rather than crawl around on the floor. I was asked to put a picture of that on the forum. I'll get around to it sometime. I'm working on my layout currently but I work in spurts - I also do RC model airplanes and it seems I go about 3 months on trains and then a similar period on airplanes. I've also been going fishing about once a week. Retirement is a busy time.


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