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Thread: reverse loop questions

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    Default reverse loop questions

    I am planing a new layout. It has been 20 plus years since I made one.

    So with DC you had a reverse toggle on the main line and a reverse toggle on the loop. Set the polarity before you enter the loop and reverse the polarity on the main line while in the loop. If you got the switches right it was smooth. Block wiring kept the other trains from reversing direction.

    Now with DCC the whole layout is on the same reverse switch. What keeps all the trains from flipping direction?

    Do the auto switch modules know what polarity to do depending on the entry point of the train? And do they also flip the mainline polarity? What happens to the rest of the trains that were just cruising on main?

    I imagine when I purchase a DCC system that I will find instructions that will make the wiring easy. However, I do not want to buy until I have plans and a date to do track work.

    Thanks
    Jeff

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    I Googled that for you:

    https://dccwiki.com/Reverse_Sections
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    Quote Originally Posted by Whitbey View Post
    Now with DCC the whole layout is on the same reverse switch. What keeps all the trains from flipping direction?
    Because it's DCC. The decoder inside the locomotive ignores which way the reverse switch is flipped and just moves forward (whatever forward is - smokestack, long hood, short hood...) when it receives a command to move forward.

    That means for DCC you don't need to flip the polarity on the main, only the polarity on the reverse loop.

    With this basic understanding, you can maybe dive into @The Ol' Curmudgeon 's link and see what more they have to say about the subject.

    Heiko

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    Quote Originally Posted by Whitbey View Post
    Now with DCC the whole layout is on the same reverse switch. What keeps all the trains from flipping direction?
    Only the reversing section gets the 'phase' changed ('phase' is somewhat similar to DC polarity -- see Ol'Curmudgeon's link). With a DCC loco the phase doesn't control the direction of the loco the decoder in the loco does. If the decoder has received the 'forward' or 'reverse' message from the command station it will continue to move the loco 'forward' or 'reverse' regardless of phase changes until told to do otherwise. The reason you can have two locos going the opposite direction on the same section of track with DCC.

    You could still change the 'phase' when the loco is in the reversing section via a switch but 'auto-reversers' such as Tam Valley's and other manufactures don't cost all that much and will do it automatically.

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    Your old DPDT setup would work fine with DCC. Better in fact than with DC because you can reverse polarity while the loco is on the block. I have a balloon track whose polarity is controlled by the turnout throw and sometimes see a slight hesitation before the engine continues.

    Auto reversers reverse the polarity when they detect a short. In theory they work with DC or DCC, but with DC you have to reverse the block that you are going to, not the one you are coming from, and that can be an insurmountable problem.
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    Quote Originally Posted by Heiko View Post
    Because it's DCC. The decoder inside the locomotive ignores which way the reverse switch is flipped and just moves forward (whatever forward is - smokestack, long hood, short hood...) when it receives a command to move forward.

    That means for DCC you don't need to flip the polarity on the main, only the polarity on the reverse loop.

    With this basic understanding, you can maybe dive into @The Ol' Curmudgeon 's link and see what more they have to say about the subject.

    Heiko
    Great answer!

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