Say I wire one of these per these directions, which are similar to many others;
http://www.ukrecmodelsrail.co.uk/modules.php?name=Content&pa=showpage&pid=23
Bottom of page.
Question; since this changes the polarity on the main line outside the loop, wouldn’t that affect any trains running there ?
I.e., change their direction ?
Yes, the polarity of the rails of the section (block) of the mainline leading to the loop (including the turnout) will reverse, so any trains in that block will change direction but only if you’re running DC (it won’t happen with DCC since direction of travel is independant of track polarity).
If your mainline is long enough, you should break it up into insulated blocks where, within each block, track polarity can be changed. This will require some extra wiring and control switches; but is common practice with DC layouts. Operating trains will take some practice as you become accustomed to changing polarities just before trains enter new blocks to prevent “stalling”.
Of course, with DCC, track polarity is not an issue when it comes to direction of travel. However, shortcircuits still have to be avoided, so measures are taken to manage track polarity changes associated with reversing loops/wyes and turntables. You can manage polarity manually (like in DC), or automatically using one of the many commercially available auto-reversers.
Thanks, great info.
So, if I’m running DC, it sounds like if I made a seperate mainline block leading to the loop, everything in that block would be reversed, but since it too is isolated, I could still have the “regular” mainline running as before I threw the loop switch.
Correct ?
DCC clarification; if I understand you correctly, with DCC, I can still have a manual toggle on a reverse loop, throw it when needed, and it will not affect any other loco’s direction of travel, when thrown ?
You can do a manual main toggle with DCC also. When you throw it, it won’t affect DCC engines running outside your loop. But…toggles with DCC dont work very well. Because of the peculiarties of DCC you wont know which way to throw the switch to enter the loop. Sometimes one way, sometimes the other. You could rig up a light. If you are DCC just get a reversing board.
If you run DC over DCC (Bachmann and Digitrax), when your loop automatically reverses for a train using the loop, it will reverse the direction of the DC trains running outside the loop!! (There are some fixes here, but it gets complicated).
Thanks !
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I agree with the web site and the comments above. I would add that you can keep the loop in sync with the main if you set the toggle switch so that it corresponds to the track switch every time. This is because the loop receives power from the main in the circuit shown on the site. You don’t need to know which way the DCC is applying power; you are simply making the loop match the main, as determined by the setting of the track switch.
In DC, OTOH, the polarity of the main has to change in order to drive the train in the correct direction coming out of the loop. The site suggests setting the controller in reverse, which will do the job. But I like my trains to run forward when the controller is in forward, so I have a reversing switch for each separately powered block. Once the train is in the loop, I throw the reversing toggle for the loop and the one for the main simultaneously without stopping the train, and then throw the track switch. This lets the train run through the loop without stopping and without reversing the controller.
Actually, my loop gets power from the controller through an on-off switch, so I can park a train there while running another train on the main. The principle is the same.
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