Wiring my 2-switch reversing loop w/dccgreenspun.com : LUSENET : Wiring for DCC : One Thread
My reversing loop includes a section of track that also doubles as part of my mainline. Thus I have a switch at each end of my reversing loop so there are 2 possible reverse polarity short circuits as a train travels the complete reversing loop. I am using a new MRC 2000 unit for dcc & power. My question is can I use an Atlas #200 relay to reverse the polarity of my reversing loop track section or must I use an auto reversing unit ?? If a #200 will work, how should it be wired to the switch(es)?? Any suggestions are greatly appreciated -- THANKS!
-- Paul Dexter (firstname.lastname@example.org), March 16, 2000
The reversing loop wiring problem is that no matter how it is initially connected, there will be a short circuit as you cross the rail gaps at one end or the other. So you must switch the polarity of the reversing loop track either before the train enters, and/or while the train is in the loop, just before it begins to exit. [With DC you actually must align both the reversing loop, then the direction of the mainline before exiting.]
Look carefully at your track plan. If your mainline path through the 2 switches does not actually reverse the direction of the train, that part of the path is not in the reverse loop and can be permanently wired with the rest of the main - No polarity switch required. Look for another (probably shorter) track section that actually causes the train to reverse directions. That's the section that needs the polarity switch. However, it should be long enough to support an entire train length (or at least the engine consist if you use plastic wheels on the rolling stock) to avoid bridging both entry and exit gaps simultaneously. The wiring for that section of track must conform to the above.
The easiest way is to control both the entrance and exit track switches simultaneously, so that only one path is aligned at a time. (Often a single switch, such as for a simple balloon loop.) Let the position of the track switch(es) control the polarity of the reverse loop track, with a relay if you chose to do so. You may still need a way to correctly realign the track switch(es) before train exit. If you have a way to do this automatically as the train passes through the reverse loop, the correct polarity would also be automatically selected.
The beauty of the auto-reverse unit with DCC is freedom from having to worry about all that switch flipping stuff while running your trains. Once you get one, you'll love it. On a one person layout, you can usually get by with only one reversing unit to service several reversing track sections. Then, as the add says says...Run your train, not your track.
-- Don Vollrath (email@example.com), March 17, 2000.
I have a reverse loop at both ends of my layout. I use a MRC auto- reverse unite on both ends.They work great. I have never had a problem with either of them. Once in a while one of my engines will throw a spark when crossing the insulated rail gap coming in or going out of the loop, but as far as running , never a hesiatation. I figured I would use a separate module for each end just in case there might be more than one train running at one time. I am glad I made that decision. The expence is not that great and when you have friends over playing railroad barrons you don't have to be concerned about shorting out one end of the loop.
-- Geoffrey(Jeff) Steuer (firstname.lastname@example.org), October 28, 2001.