Back-to-Back ARs?


 

Hello,

I’m looking for advice on how to wire a classification yard. As the photo (Back-to-Back ARs?) in the Photo Folder shows, the mainline passes around the yard to the left. With its’ two connections to the mainline the yard now becomes a large wye. To complicate the situation, the yard includes a turntable. Putting the yard and the turntable on auto-reversers seems (to me) to create a potential AR conflict. What should I do?

As always, be in good health and do good work.

-Michael Boyle

      The miracle is this: The more we share the more we have.
                      Leonard Nimoy


wirefordcc
 

Hi Michael,

What kind of turntable do you have?  If you have a Walthers, the turntable handles the reversing for you and does not use an auto reverser.  Turntables that use split rings for power pick up also don't need an auto reverser.  Other turntables may be best served by an auto reverser.  We'll discuss that if you don't have one of these turntables.

Allan Gartner
Wiring for DCC


 

Hello Allan,
Thank you for your help.
The turntable is made by Custom Model Railroads and the wiring diagram indicates that an AR is required.
- Michael


Don Vollrath
 

Michael, simply isolating and wiring that single straight track section leading to the turntable to be fixed polarity solves the issue.

DonV


 

Thanks Don,
If I am understanding this correctly, the yard would be on an AR and the turntable would be on another AR?
-Michael


Tim
 

You don't need to make the whole yard a reverse section. Put double gaps on all three tracks leading into the 3-way switch at the center. The reversing section would be the three way switch and the two tracks to the right of it, including the turnout. The track from the three way switch to the turntable is wired to one of the tracks on either side of it. It doesn't matter which one. Now you can safely put the second AR on the turntable.

I would use a relay connected to the switch machine on the three way switch rather than an AR to control the polarity on the three tracks to the right, but I'm allergic to ARs. :) Reconfiguring the turntable to eliminate the AR sounds like it would be a little more work.

Tim Rumph
Lancaster, SC


 

Thanks Tim,
That is an excellent idea. Most of the time it will only be locomotives entering that central section, the classification tracks are on either side of this peninsula. I'm interested in your preference to avoid ARs. Care to elaborate?
-Michael


Tim
 

ARs operate by detection of short circuits in the track power wiring, which is something I prefer to avoid. A relay connected to the switch machine insures that the polarity is correct for whatever route the turnout is lined for. In this case, only one train or engine can move into the reverse section at a time, since there's only one turnout providing access to that area. If the switch is lined properly, the polarity is lined correctly as well.

Also, a DPDT relay with a ridiculously high voltage and current rating (12 A at 240 VAC with a 12V coil) is $6 or so. Since there's never a short, there's no chance of the AR conflicting with the circuit breaker for the power district.

The reversing needs of turntables has been discussed already.

Tim Rumph
Lancaster, SC


whmvd
 

Another (seldom mentioned) reason for not having a reversing sections with a lot of tracks (and therefore potentially a lot of locos) is, that an AR unit has its own maximum current, which is usually considerably lower than the command station's. A large number of locos with lights and sounds on is going to make a dent in the capacity.

Wouter


On Mon, 7 Jun 2021 at 15:50, Tim <tarumph@...> wrote:
You don't need to make the whole yard a reverse section. Put double gaps on all three tracks leading into the 3-way switch at the center. The reversing section would be the three way switch and the two tracks to the right of it, including the turnout. The track from the three way switch to the turntable is wired to one of the tracks on either side of it. It doesn't matter which one. Now you can safely put the second AR on the turntable.

I would use a relay connected to the switch machine on the three way switch rather than an AR to control the polarity on the three tracks to the right, but I'm allergic to ARs. :) Reconfiguring the turntable to eliminate the AR sounds like it would be a little more work.

Tim Rumph
Lancaster, SC


 

Thanks to everyone for your most generous assistance.
So the conclusion I've come to is that the turntable will be on an AR. The track from the turntable to the three-way will be on the same power district (breaker protected) as the surrounding yard tracks. The engine service tracks, to the right of the three-way, will be on their own AR.
Once again,
a sincere "thank-you."
Michael Boyle


john
 


Turntables generally reverse their own polarity at halfway through their rotation. If you pull onto a turntable bridge, then rotate 180 degrees your bridge will be at it original N / S orientation. Your engine, if powered, will move back where it came from as if you lifted it and turned it around. An auto reverser is not required for the bridge. Unless you have a reverse loop or a "Y," you do not need a auto reverser. 

Think of it this way, Rail Roads only travel East and West and they have a North and South rail. That way it is easy to keep its orientation. 

On Monday, June 7, 2021, 10:29:41 PM EDT, Michael Boyle <boyle10017@...> wrote:


Thanks to everyone for your most generous assistance.
So the conclusion I've come to is that the turntable will be on an AR. The track from the turntable to the three-way will be on the same power district (breaker protected) as the surrounding yard tracks. The engine service tracks, to the right of the three-way, will be on their own AR.
Once again,
a sincere "thank-you."
Michael Boyle


Jim Betz
 

Michael,

  I would "re-wire" (simply re-gap?) the turntable so that it is a "split ring"
style of turntable.  Yes, this can cause a 'hiccup' in the sound as a loco
is turned.  My response is "so what?" ... as in just how often are you
going to be turning engines and do you really care?  My $,02.
                                                                                                        - Jim