Layout Reverse Engineering

Donstaff Oct 23, 2020

  1. Sumner

    Sumner TrainBoard Member

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    Good point.

    The more I think about it I'd mess with the part of the wye that I put in blue and move the south end of it down further making the reversing section longer but...... saying that Andy are you suggesting the following?

    [​IMG]

    That does look like it would work except if that is too large of a power district for some reason. If it was mine I probably would want two boosters and circuit breakers assigned to that much track unless I'm the only one ever running and there wouldn't be many locos running at the same time in that section.

    I'll be a single user myself (maybe one other at times) but will have my layout divided into 3 power districts with separate boosters and circuit breakers even though I probably don't need to do that.

    Sumner
     
  2. BigJake

    BigJake TrainBoard Member

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    Yes, that's where I'd make the isolation cuts/joiners (right at that the thru and diverging routes of the switch), but if the OP already had insulating joiners where he had them, it would work practically as well (except remove the isolation joiner pair near the East Berlin yard). By putting the isolation gaps/joiners right at the switch, it makes it very difficult to physically get two trains to simultaneously short both routes.

    Your point about power district capacity (and capacity of the AR unit) is well taken, and could be an extra work/cost.

    All power districts in that left loop would need to be auto-reversed together. I would set up a single district that was auto-reverse controlled (that adjoins the two isolation gaps), and run the other district's boosters off of that district's power, so they all reverse when the AR district reverses.

    Same thing with multiple circuit breaker power districts, from one or more boosters that follow (take DCC input from) the AR controller at the wye.

    But IMHO, the benefits of making it very difficult to accidentally get two trains bridging both isolation gaps would be worth it.
     
  3. Donstaff

    Donstaff TrainBoard Member

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    I have removed the cut (insulated rail joiners) at the entrance to the East Berlin yard in this drawing. That, I believe, isolates the left side of the wye from the right side. Is this what you were suggesting to eliminate the possible problem with a long train pulling out westbound from the yard? Do you thinks what I have shown here works?
     

    Attached Files:

  4. BigJake

    BigJake TrainBoard Member

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    Donstaff,

    Yes, what you have shown will work.

    But you have one more insulated joiner pair than you really need, because of where you are putting them. And their placement makes it more likely you can get two trains shorting across insulating joiners in two legs of the wye.

    If you remove the two insulated joiner pairs shown between SW9 & SW8 and between SW8 & SW78), and instead install one pair of insulated joiners between SW8 & SW2, that's all you need (in conjunction with your pair of insulated jointers between SW2 & SW3)!

    In fact, I would put both pairs of insulating joiners as close as practical to the left two ends of SW2. Ideally, you want it as difficult and unlikely as possible to physically get two trains shorting both pairs of insulating joiners at the same time.
     
  5. Donstaff

    Donstaff TrainBoard Member

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    Thanks BigJake,

    That is good news, as what I showed in the drawing was just to illustrate my question. Actually, the way you suggested as the best is how I have it wired right now, with the exception of actually replacing the insulated joiner pair with regular joiners at the east end of the bridge where the East Berlin yard begins.
     
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  6. Donstaff

    Donstaff TrainBoard Member

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    BigJake,

    Following up, if I understand, removing the insulated joiners next to the East Berlin yard, in addition to reddening or eliminating the chances for a long westbound train from bridging the gap and causing a short, it also makes the right side if the wye and the entire yard into a switched block. So, when an eastbound train crossed the insulated rail joiners, it will flip the polarity of the right side of the wye and the entire yard. Is that correct?
     
  7. BigJake

    BigJake TrainBoard Member

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    If wired as I suggested, the E Berlin yard, Midway Intermodal, and the upper right switch to they wye, are all part of the only power district that never switches polarity.

    The power district that includes the entire left loop, with all of the wye except its upper right switch, reverses polarity to match whichever leg of the upper right wye switch is used to enter/exit that loop.

    Note that some switch machines include a DPDT switch (or a control for an external DPDT relay) which can be used to control the polarity of the reverse loop based on which way the switch is thrown, rather than forcing a track short that triggers an auto-reverser module to swap polarity.

    And of course, the Pigeon Mtn loop is also still a reverse loop.
     
  8. Donstaff

    Donstaff TrainBoard Member

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    Thanks BigJake.

    Still having a little trouble fully understanding how the MRC 520 reversing module that I have installed on the wye works. As per the attached drawing, I have the red wires of the reverser connected to the buss and the yellow wires connected to the isolated section between the two insulated joiners on the wye and the end of the bridge leading to the East Berlin yard. The insulated joiners at the end of the bridge are still in place right now. When I replace these with regular rail joiners, that will connect the yellow side of the reverset section to the yard. The MRC 520 wiring diagram shows the red wires connected to the buss and the yellow wires connected to the reverse section. Do I need to reverse the wiring, and have the yellow wires connected to the loop, or does it matter?
     

    Attached Files:

  9. Sumner

    Sumner TrainBoard Member

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    [​IMG]

    I believe that what Andy is suggesting is what is shown above (Andy correct me if I'm wrong).

    You have a large layout and even if I was the only operator I'd want to break it down into power districts to make it easier to locate shorts and to also have the ability to have boosters if the current draw during operations was heavy. Wiring the whole left side of the layout as one large reversing district I believe will work but that means all of the current to the track to all of that track will be going through the MRC 520. According to the manual it will handle 5 amps so maybe you are just fine.

    Also you could probably take the yellow output to the reversing districts and run it through circuit breakers (something like what Tam Valley sells for under $40) if you wanted to break up all that track into more than one power district.

    Also MRC shows running the red wire to the track (or buss) outside of the section that will reverse. I showed that above but again now that section of track (to the right of the isolation cuts) would be supplying power to the whole reversing section, the section that it is composed of down to the other reversing section and possibly that section also if it is connected to that track.

    If you follow the plan above I'd run the yellow wires off the MRC to a buss that would run around the large part of the layout on the left (not shown above) and run multiple feeders off of it to the track there.

    What is your overall power distribution for the layout and how is it wired now and what do you see for the future? Again you have a large layout with lots of track and the possibilities of running a number of trains at the same time. If it was mine and I was the only user I'd have it broke up into at least three power districts and probably 5 or more.

    Sumner
     
    Last edited: Mar 21, 2022
  10. BigJake

    BigJake TrainBoard Member

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    A conventional Auto-Reverser conveys power from a DCC bus that is not subject to reversal, through a short circuit (e.g. excess current) sensor, through a DPDT switch, to the reversible track. The excess current sensor, when tripped, simply throws the DPDT switch to the opposite polarity from what it was before the short occurred.

    Therefore, if the AR supplies only the control inputs to a booster, that in turn supplies the tracks to be auto-reversed (and shorted), then the AR will never see the short for the booster.

    On the other hand, if the AR is situated between the booster and the reverse loop trackage, then that will work fine.

    Any circuit breakers used on the reversible bus should "trigger" more slowly than the AR takes to sense the short and reverse polarity of the reversible bus, otherwise, the CB will trip earlier and prevent the AR from seeing a long enough short to act upon. Fortunately most (but not all) ARs are fairly fast-acting, and most (but not all) CBs are slower-acting.

    Multiple, independently auto-reversing districts in the reverse loop will not work, because the controllers of two adjacent auto-reverse sections will both try to switch their polarity in response to a short, and they will stay opposite each other, continuing the short across that boundary. Two or more independently auto reversing regions should never be adjacent to each other. That means the auto-reverser needs to be able to control the entire current needed by the entire reversing loop. 5 amps seems sufficient to me for N scale.

    However, the ability to narrow down the region of a short circuit in a large loop is helpful in finding and correcting the short, and circuit breakers for individual sections of the reverse loop (as long as they are compatible with the AR controller) would help, particularly if they can provide a visible indication that they have tripped. These CBs would be downstream of (and powered by) the AR controller.
     
  11. CSX Robert

    CSX Robert TrainBoard Member

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    I am not a fan of auto reversers because they detect a problem and fix it, I would prefer when possible to prevent the problem to begin with. With the entire left side of the layout the reversing section isolated at the right side turnout of the wye, it's correct phase is simply determined by the direction that turnout is thrown. Since you have to throw the turnout anyway, I would have the throwing of the turnout also control the phase of the reversing section. There are multiple ways of doing that depending on how you throw the turnout. Even if there's not a handy way of doing it (say for instance the turnout is thrown by hand), I would prefer a DPDT switch over an auto reverser. That would make it two-step process to throw the turnout, but I would still prefer that over the short detection and correction. It would be a simple project to add a green and a red LED to show when the phases match or don't match so you don't forget to switch the phase after throwing the turnout.

    An advantage of not using an auto reverser as described above is you can switch the phase of the low power DCC signal instead of the booster output. You could then feed that signal into multiple boosters to have multiple boosters in the reversing section.
     
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  12. BigJake

    BigJake TrainBoard Member

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    Thanks Robert, for expanding on the advantages of linking the control of the switch with the control of the polarity of the loop power.

    I would further suggest another option for manually controlled turnouts, is to turn the problem around, so to speak, and have the control that flips the polarity also control the position of the switch. Just another way of looking at a problem where two things need to be controlled in concert.

    I especially agree that in a situation such as this, with the substantial amount of current required by the reversing loop, desire for multiple, lower-power districts within it, etc., linking the polarity control to the switch polarity (or vice versa) is a simpler and superior solution.

    That said, there's no reason the polarity of the other reversing loop could not be controlled in a similar manner. But if an auto-reversing loop controller is already in place for that loop, and it works well, there's no compelling reason to rip it out and replace it with something else.
     
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