# Reverse Loop Questions?



## Bigfoot21075 (Aug 7, 2021)

Hello All,

I THINK I have a reverse loop in my layout design. It is the segment that cuts through the center of the layout. I THINK it can change the direction of a train going either direction. I am going to use DCC, how does this work? Even with DCC the polarity is still reversed at some point on that stretch correct? Or does the computer handle it all with a sensor? Do I need isolate that rail section? If it reverses polarity, how does it not affect any other train on that line (or if one of the crossovers is activated)? Whew......

This is almost as complex as ham radio 

KC3MXI


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## mesenteria (Oct 29, 2015)

The way you handle this electrically is to reverse the phase in DCC between the two turnouts on either end of the reversing diagonal. You have to gap the turnout at its diverging route after the frog, and then power the central diagonal, only, using either a DPDT toggle switch or a reversing unit that operates automatically ($$).


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## DonR (Oct 18, 2012)

A reverse loop with DCC is all automatic when you
use a Reverse loop controller.

As Mesenteria has stated, gap or use insulated joiners
between the crossing track and both turnouts to which
it connects. This isolated section is then powered by
the reverse loop controller which takes it's power from
your DCC track bus. It is totally automatic. Once
installed you can forget about it and just run trains.
That is part of the technical wonder of DCC and why
it has basically taken over the model train hobby.

The DCC track is a modified AC...it also carries the
digital information the loco's on board decoder uses
to control the motor. Thus the 'phase' of the track
has no effect on the direction of the train. The decoder
ignores the phase. Just as a table lamp will light no
matter which way the plug is in the wall outlet.

Don


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## CTValleyRR (Jul 26, 2014)

Yes, you have a reversing loop. Follow Don's advice above.


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## Bigfoot21075 (Aug 7, 2021)

I was messing around with this some more, there is a way I can make it a true 2 direction reverse loop without having to back trains up. I am just not sure if I can make that look good on the layout or not. Attached.


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## DonR (Oct 18, 2012)

Yes, your change does make it possible for a train to reverse
direction regardless of it's original direction. But, in doing so
you have created a 2nd 'reverse loop'. That means you'll
need two reverse loop controllers. However, you have a
very unusual situation in the upper left where the two isolated
sections are separated only by a turnout. While they are not
abutting (which would result in a short circuit) they are very
close together. A long loco or lighted passenger car could span the turnout and 
cause a short circuit between the two iso sections. If you could add a section of
straight to the upper left turnout the shorting problem would
be solved. Incidentally, that turnout (and any added track)
would be powered by your main DCC bus.

A second solution is equally undesirable. Making the entire
X tracks one 'reverse loop'. This is not advisable since you
would have three access points to the iso section and increased
likelyhood that two locos would try to enter the iso section at
the same time, resultng in a short circuit.

So, in my opinion, add track to the upper left turnout
and go with the 2 reverse loops.

Don


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## DonR (Oct 18, 2012)

I did it again... I goofed...

Bigfoot...I did more thinking and realized that the
situation where your isolated section comes from lower Right
to upper Left will work fine just as you have it shown in your
drawing. There is no need for an additional section of track to
avoid a short circuit as I had advised in my post #6 above.

Explanation: When loco from lower left reaches the upper right
turnout the reverse controller will match phase of the iso section
to the turnout main DCC. Then when the loco moves to the
gap between the upper right turnout and the second isolated
section the second reverse controller will also match phase with the
turnout DCC main so, even with a long loco or lighted passenger
car, there will be no short. 

It is true that two isolated sections cannot abut since loco wheels
will cause both controllers to try to match phase but can't. However,
in the present case even the short turnout powered from the main
prevents the controller 'fight'.

You will, of course, need gaps on both sides of the upper left turnout,
at the lower right turnout and at the upper right turnout in order
to create the two isolated sections.

So sorry for the confusion.

Don


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## Bigfoot21075 (Aug 7, 2021)

DonR said:


> I did it again... I goofed...
> 
> Bigfoot...I did more thinking and realized that the
> situation where your isolated section comes from lower Right
> ...


Don,

I can't thank you enough! Your fantastic, clear explanation was great. Even I could understand it. I APPRECIATE your insight and taking the time to help a newbie out. This forum is an AMAZING resource, I haven't been this excited about a new project in a long time.

Rob


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