Model Railway Double Reverse Loop Wiring How to wire two reverse loops on your two-rail layout for automatic operation

Here we show you how to wire the reverse loops and track switches on a double-loop layout with a single connecting main line. Wiring a reversing loop (or turn-around track) may seem complicated, but if you take one step at a time and chek your work, you will have a fully automated reverse loop and worry-free train operation.
 
[Click here to review reverse loop fundamentals]
 
Here are three plans for a 'dog bone' type layout with a single track main line: All systems are completely automated, with automatic control of the track polarity and the track switches (or 'turnouts').
 
The first system is an economical choice for:

• DCC layouts
• DC layouts that do not require manual control of the turnouts
     [Click here for a system with manual turnout control]
• DC or AC layouts with single cab control (one train power pack)
     [Click here for muti-cab control layout wiring]

Double reverse loop control for DC, DCC or AC layouts, with slow-motion switch machines and no manual switch control.

This system, shown above, uses a DPDT relay to control polarity of the main line. Slow-motion switch machines (required) powered by twin DC power supplies operate the track switches simultaneously. To use solenoid-operated 'snap' switch machines, see the system below.
 
When the relay is 'off' the main line polarity will match the loop polarity at points marked 'M', allowing trains to cross at those locations.
 
When the relay is 'on' the main line polarity will match the loop polarity at points 'X', allowing trains to cross there.
 
The relay turns on and off as the track switch points are changed from left to right. The relay and the switch machine are operated automatically by the MRD2 dual train detector.
 
Wire the switch machines so the switch points are aligned for the 'M' junctions when sensor 1 is triggered. If the points align the wrong way, swap the connections to the switch machine.
 
How it works: Assume a train is moving left-to-right on the main track, approaching the east loop, and the turnout is aligned with 'M'.
 
The train enters the loop and travels counter-clockwise. When it triggers sensor 2, the MRD2 will throw both switches to align with 'X' and will turn on the relay. The main line and loop track polarities will now match at the two 'X' locations. The train returns to the main line.
 
Now the train approaches the west loop, moving right-to-left. The switch points are still aligned to the 'X' junctions and the track polarities still match there.
 
The train travels counter-clockwise around the west loop and triggers sensor 1. The MRD2 throws both switches to align with the 'M' junctions and turns off the relay. Mainline and loop track polarities now match at points 'M' and the train returns to the main line.
 
Manual control of the turnout is possible, as shown in the MRD2 installation instructions. For AC single cab and DCC powered layouts, this is all you need.
 
For DC layouts or AC layouts with multiple cab controls, see the note below.

Double reverse loop control for DC, DCC or AC layouts, with 'snap' twin-coil switch machines and no manual switch control.

As in the system shown above, trains always travel around the loops in the same direction every time (counter-clockwise in this example). This system is for layouts that have twin-solenoid switch machines.

The Azatrax circuit modules require an accessory power supply, 9 to 15 volts, AC or DC, separate from the switch machine power supply.

MREV Polarity Controller	$32.50
MRD2 Dual train detector • Includes two infrared sensor pairs (IrLEDs & photo-transistors)	$36.50
Accessory power supply, PS1206 • Regulated 12vdc, 600mA, slim plug-in • One supply can power a dozen Azatrax circuit modules	$9.50
Package for Double Reverse Loop with MREV Controller Automatic switch control only, no manual control: • One MREV polarity controller • One MRD2 dual detector with IR sensors • One PS1206 12vdc regulated power supply	$74.00

This complete automated control system for a layout with single main track and twin reverse loops can be used with any type of switch machine and is fully compatible with DC, DCC and AC layouts.
 
Track polarity is controlled for both the main line and the loop tracks. The turnouts can be thrown manually without affecting a train on the main line.
 
Use this system if:

You want to be able to independently throw the track switches manually without affecting a train on the main line, or,

You have an AC or DC layout with two or more cab controls.
   [Click here for muti-cab control layout wiring] Otherwise the single relay system above will work fine for less money.

As in the system above, an MRD2 dual train detector controls the track switches. Now MRD1 single detectors are added on the main line just ahead of the points end of each switch.
 
All detectors are connected to the MREV Polarity Controller. Track power to both the main line and the reversing loops is routed through the MREV circuit.
 
Wire the switch machines so the switch points are aligned for the 'M' junctions when sensor 1 is triggered. If the points align the wrong way, swap the connections to the switch machine.
 
How it works: Assume a train is moving left-to-right on the main track, approaching the east loop. It will trigger sensor 6, alerting the MREV to change the loop track polarity according to the east switch position. The MREV gets the track switch position info from the MRD2 dual detector.
 
The train goes around the loop and approaches the east switch, ready to return to the main line. It will trigger either sensor 2E or sensor 1E. This causes MRD2 #2 to throw the switch, and the MREV will change the main line polarity so the train can exit the loop without interruption.
 
As the train continues from right to left on the main track it approaches the west switch and is detected by sensor 5. Similar to what happened at the east loop, the west MRD1 train detector alerts the MREV that a train is approaching the west loop. The MREV adjusts the polarity of the loop track to match the main line polarity. The train goes around the west loop, and as it approaches the switch, MRD2 #1 will throw the switch and alert the MREV to change the polarity of the main track.
 
The MRD2 and MREV circuits have non-volatile memory. They remember the switch position and polarity settings when layout power is turned off.
 
Components for the single reverse loop control system may be ordered separately or as a package. Detector circuits and the MREV polarity controller require a power supply, 8 to 15 volts AC or DC.

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