Turntable and Reverse Loop

Discussion in 'DCC & Electronics' started by Bob Collins, Mar 4, 2005.

  1. Bob Collins

    Bob Collins Active Member

    I am about ready to get started building my new layout and I mentioned to a fellow modeler here that I was not going to have any reverse loops in this layout ( I model HO and will be using Digitrax Super Chief DCC). Later we were talking about the fact I intend to use a turntable, I hope to purchase the new Walther turntable, and he told me in using a turntable I have created a reverse loop. Is this right? If so, where does one place the reverse loop module?


  2. Fred_M

    Fred_M Guest

    Yes, but no module. As you rotate a lokey the switches and contacts in the turntable will travel around with the lokey as it indexes around. And since DCC isn't rail polarity sensetive you won't even need to punch the reverse switch. Drive in, stop, rotate 180 and drive out. The contacts in the table will take care of the rest. Fred
  3. Bob Collins

    Bob Collins Active Member

    Great, thanks Fred. Guess I can set the module aside for another day :)

    Or better yet I ought to sell it so I can begin to collect my funds to buy that Walthers turntable. $300 ain't chicken feed :rolleyes:

  4. SteamerFan

    SteamerFan Member

    Yes it's a reversing loop, wire an auto-reverser into the power leads for the Turntable itself, thus switching the turntables rails as needed.
  5. nolatron

    nolatron Member

    I've got an Atlas TT installed on my layout and have a reverser on order from Tony's Train Exchange. As the table turns, the contacts under the table on the rails will switch connectors, thus reversing the polarity, so a reverser is needed.

    I'll take a guess and say the walther's is probably the same.
  6. Bob Collins

    Bob Collins Active Member


    I'll keep my Tony's reverser handy and will know the answer as soon as I can afford the turntable. :)

    I also appreciate Steamer fans comment about where to wire in the reverser, if needed. :)

    I'd better get cranked up getting my benchwork completed or all this conversation about modules and turntables won't mean a whole lot. I have my materials list completed and will go to the lumber yard on Monday. Too many guys buying supplies to complete their honey do lists at the hardware store on Saturdays :rolleyes: :rolleyes:

    Thanks again.

  7. Fred_M

    Fred_M Guest

    Let's think about this. My gallows get power from the lead in tracks. When the gallows is aligned with the track the contacts on the table supply power to the right and left rails on the gallows from the lead in track. You drive on and park. You now rotate the table and the contacts are broke and reconnect as the table spins to the other index points. When it turns 180 degrees it once again connects to the contacts of the track you drove in on. The right rail is now the left and vice versa. The table contacts have acted like a double pole double throw center off switch wired as a reverser. But in DCC rail polarity don't matter so even though the right rail is now the left rail when the decoder gets the powerup signal the lokey resumes in the same direction of travel it entered the table. So if it entered short hood forward it will leave short hood forward. So we can think of a turntable as a double pole double throw mechanical switch. So no module is needed. See? are not Atlas tables wired that way too? Fred
  8. SteamerFan

    SteamerFan Member

    Umm..Fred, polarity still applies in DCC.

    take the following:
    +++++ +++++ +++++ Turntable at 0 degress, all rails align properly.
    ------ ------ ------

    +++++ ----- +++++ Turntable at 180 degress, rails no longer aligned properly.
    ------ +++++ ------

    Since you still have a positive and negitive bus line, you must reverse the turntables track polarity to stop any shorts when the train leaves the turntable and enters any track outside the turntables tracks. Yes it does not matter which rail is positive and which is negitive for direction, but it does matter for short faults.
  9. Fred_M

    Fred_M Guest

    But the rails get their power from the inlet track.
    So ++++ ++++ ++++
    ____ _____ ____

    The + on the ends feed the middle, same with the ----

    Rotate 180 and the track that was +++ in the center reconnects with the ---
    and vice versa. No shorts because the inlet tracks feed the gallow's track, It goes dead when it isn't aligned. So the +++ side becomes the --- side, just like in a DPDT reverse switch. It's the way my table works. Come see it.
  10. SteamerFan

    SteamerFan Member

    that is not good fred, you're saying that an engine will have no power when the turntable is not aligned to a track. which means you will have a constant Ligh on, light off, light on as the track rotates around. this is not good for not just the light, but also the fine electronic DCC circuit board, which as soon as it get's power goes through a start up procedure, get's interupted then has to start all over again. If thsi is a sound board, you may short your DCC system out, as it really draws alot of power on start up.

    It is far better to have constant power the Turntable track and to use a reversing module to reverse the polarity as the Table roatabes. This allows the Loco to continueto have it's lights on as it rotates, as well as preserves the integrity of the Electronics.

    Your system may work for you, if you don't mind reducing the life expectancy of your DCC boards or shorting the Boosters out or don't mind the flickering ligyts of the loco, but other prefer a stronger, safer better working method.
  11. Bob Collins

    Bob Collins Active Member

    Well, since I have the module and no plans at this time for a reverse loop or a wye, why don't I connect it to the power lead into the turntable and see what I get. I do appreciate the conversation the two of you have had, as it certainly has enlightened me about what can go wrong with something like this thats seems so simple to an novie like me.

  12. jwmurrayjr

    jwmurrayjr Member

    A turntable is a reversing section.

    Some TTs have reversing circuits build (Atlas and the New Walthers???). Some don't like the old Walthers like I have. It needs an A/R module wired just like a "standard" reversing loop (Wires to each rail and wires to the track bus or main track.

  13. Fred_M

    Fred_M Guest

    So it's not reliable? ROFLOL.
  14. interurban

    interurban Active Member

    Hi Bob, I am starting all over again too, :) I will keep me beady eye open for more post from you and pics of progress.

    Glad you went DCC.
  15. Bob Collins

    Bob Collins Active Member

    I went to my first operating seesion of the club I have joined here. Great fun, although for this first time I keep my hands off of the throttles. The club has a LARGE layout on the upper level of the old Rock Island depot here in Council Bluffs. It is sort of old and needs some work, but I like the group and they seem interested in getting the layout back up to speed.

    I will begin to post some pics as soon as I actually begin to get things in order. I really hope to buy the bench work materials this coming week and get cranked up immediately. I won't be working at warp speed like some do, but steady progress is my goal.

  16. Fred_M

    Fred_M Guest

    That's the way to do it Bob, it's a hobby. :) Fred
  17. 60103

    60103 Pooh Bah

    The turntable rails have to be matched with the lead-in/stall track rails. Doesn't matter if they call it polarity or north-south.
    There are three types of turntable wiring.
    One has contacts on the bridge that touch the lead-in tracks as it turns. No alignment problems. Not sure who makes them.
    Second type has split rail/split circuit board power to the bridge. This is Atlas, Peco, and sounds like some Walthers. This one does its own aligning of polarity.
    Third type has two wires that permanently attach to the bridge rails. (Also if you built the pivot using a Stereo plug.) The old Wilson turntables are like this. This one requires a separate reversing switch, either a DPDT for DC layouts or a module for DCC. We just wired the module to the track wires and it switched over whenever the loco entered or left the table.
    Any other wiring methods?
  18. nolatron

    nolatron Member

    Just wanted to confirm you don't need a reverse for the atlas turntable with DCC.

    I hooked mine up, with the the leadin rail isolated, and all the spurs with their own feeders. As long you wire the - and + rails for everything properly, you won't have any problems I discovered.

    The rail for the table switch polarity at the 1/2 way point (rails pointing straight to the shed, turning CCW, will switch before hits next spur) and the reverse wiring of one half the spurs from the other half works fine with straight wiring. pretty cool.

    Now I got auto reverse I need to find a use for :)

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