A Reversing Loop issue.

Discussion in 'DCC Control' started by Splitpin, Jul 6, 2018.

  1. Splitpin

    Splitpin Full Member

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    Hi All
    Just run into this issue and wonder if anyone has experienced anything similar.
    I'm at that stage of layout development where I need to start detecting the end of trains as well as just the loco for my block detection / autotrains running. So as a quick and not cheap test/start I bought one of the Hornby Illuminated Pullman coaches, and beautiful it certainly is. However it seems to be causing me a problem.
    I have 2 reversing loops managed by 2 Lenz LK200 rev loop devices, and they work just fine with all my locos no problem at all. But the Hornby coach manages to trip a 'true' short every time the polarity isn't right anyway, and stops the layout. I don't understand why the coach would behave differently to say a loco and pickup equipped tender - about the same length, pickups on all wheels - what's the difference ?
    Also "it's just the coach". If I just manually wheel just the coach itself back and forward over the RLoop start rail break it trips too.
    So hmmm …. ???

    TIA
    John
     
  2. RFS

    RFS Full Member

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    Is this one of the latest Pullmans, and if so does it actually have pickups on all 8 wheels? All the lighted Hornby Pullmans I've got have LH pickups only on one bogie and RH pickups only on the other.
     
  3. Splitpin

    Splitpin Full Member

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    Hmm thanks Robert. I dunno, and ummm how can I tell. There's a bridge rectifier in the coach circuit I believe which will defeat my multimeter, but I'll play and try and work it out. As to new … hmm bought new in NZ 3 weeks ago, but how long it had sit on the shelf, who knows. It's Hornby R4738 'Minerva'.
     
  4. paul_l

    paul_l Staff Member Administrator

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    Hi John

    Try lifting one bogie clear of the track, if the lights stay on then its picking up from all wheels.

    What happens if you run two loco's (double headed) over the loop ?

    Paul
     
  5. RFS

    RFS Full Member

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    All my Pullmans have a pickup bar across the centre of the axles. The wheels are live on one side and insulated on the other, with the wheels on the other bogie being the reverse of this. This also means that both live wheels on each bogie are electrically connected.

    But having said all that I can't see why you have the problem.
     
  6. Dr Tony

    Dr Tony Full Member

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    You say the coach is new. Does the illumination work at all? I had a similar issue with an illuminated guards van right out of the box. It had the same sort of pickup arrangement as yours. My problem was that one of the axles was installed the wrong way round in the bogie. Check each wheel with a multimeter to check if the isolated wheel is on the same side of the axle for each bogie, alternating which one is live for each end of the coach to make a circuit.
    It may be as simple as that.
    Cheers
    Tony
     
  7. Splitpin

    Splitpin Full Member

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    Oh DOH! :hammer: Of course. And … the lights go out.

    Double Headed - ummm dark art, but I'll give it a go. I did in small boy fashion, try many times to run 2 loco's simultaneously into opposite ends of the loop and nothing missed a beat. I had total faith until the coach incidents started to mount.

    Further … just arranged some double heading tests and happy to report no problems at all.
     
    Last edited: Jul 7, 2018
  8. Splitpin

    Splitpin Full Member

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    Later that afternoon...
    Taking the multimeter to the coach .. indeed opposite sides on opposite ends, 4 wheel pickups only and no reversed axels. Do later versions have 8 wheels Robert ?
    Would that make a difference I wonder?

    I can see a difference between this coach and say a fully pickup'd loco and tender though.
    With the coach, it spends a period of time, maybe the best part of a second with 'a foot in both camps', but only one foot in each camp.
    The loco on the other hand has feet in both camps at all times effectively, having full length contact both sides.
    I have no idea what that might mean having no real grip on how sparks work, especially here with the electronic management of the short in the first place.

    Even more surprised that if this is an issue … well I couldn't find with Google, so it can't be true.
     
  9. SMR CHRIS

    SMR CHRIS Staff Member Moderator

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    You may have to look at a new solid state Auto reverse unit had a similar trouble with Lenz auto reversing unit on a club layout as it uses a relay to do the switching and the speed of detection/switch over, isn’t quick enough with the low draw of coach lights makes a short through the car from one side pickup to the other side, as in deferent section and the reversed wave for = short, leave it there long enough and you may see magic smoke

    Haven’t had the issue since switching the club layout to PSX-R units.
     
  10. Splitpin

    Splitpin Full Member

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    hmm bugger, I understood the Lenz LK200 ones are good, never had a issue till now. However thanks for the info especially your experience of it exactly- bugger again, I knew money would fix it :facepalm:
     
  11. RFS

    RFS Full Member

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    The LK200 is a solid-state reverser. It's the older LK100 which is relay-based.

    However, I don't understand how the problem occurs. Surely the coach is part of a train, and the engine will have triggered the auto-reverser first, so by the time the coach enters the loop the polarity should be set correctly? It's a requirement of any reverse loop that the whole train is contained within the loop. Is the loop long enough for this train?
     
  12. Splitpin

    Splitpin Full Member

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    hmm Very Good point Robert. And yes no worries on length the train is barely half way into the block .
    I do have 2 reverse loops , both have their own LK200. One is an admittedly complex station entry, but the other is a dead simple classic reversing loop and the same thing happens.
     
  13. RFS

    RFS Full Member

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    Just to confirm something else - there are IRJs on both rails at both ends?

    My only thought now is that the current inrush from the coach when it enters the loop is triggering the module. I don't know whether your coach has the later LEDs but mine have the older-style lamps and current drain is quite high. But having said that, I would have thought the issue would have been well known.

    You might need therefore to turn off the lights. Easily done - just reverse the axles on one of the bogies.
     
  14. paul_l

    paul_l Staff Member Administrator

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    You may have to ensure the whole train is in the loop before triggering the auto reverser

    Paul
     
  15. RFS

    RFS Full Member

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    If the polarity is wrong on entry, it will be triggered immediately then. The polarity reverse will always be triggered on exit (ie when the loco crosses the IRJs there). The only requirement is that when the polarity is triggered on exit, the whole of the train is in the loop between the pairs of IRJs.
     
  16. Splitpin

    Splitpin Full Member

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    Here's the track plan, there's more but I hid that for clarity.
    Yes double insulating rail joiners at the entries and exits - marked here with red.
    As I said the classic rev loop on he left and the more complex one through the middle which is a station.
    I call that junction at the station throat 'Nightmare Junction' because it has been - but it all works beautifully now - apart from this one coach.

    Note: It's only been 1 week since I finally completed all the wiring and started running trains, but I have had 4 trains running simultaneously under automation - so it all works - but I don't know my own layout very well yet, if you know what I mean.

    rloops.jpg
     
  17. RFS

    RFS Full Member

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    Does the coach work OK on the classic loop on the left?

    And as far as turnouts are concerned, do they have live frogs (Electrofrog) and if so is the polarity being properly switched rather than relying on blade contact? It's possible the short might be being caused by shorting on the entry points rather than anything to do with the auto-reverser.
     
  18. Splitpin

    Splitpin Full Member

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    No, the coach trips in the classic loop too.
    All track is Peco Code100, all points/turnouts are Electrofrog, apart from the double slip and the long crossing where Peco only make Code 100 Insulfrog unfortunately.
    Points wiring: I'm in the school of thought that you can overcomplicate things, but yes blade switching. I do follow what Peco and others advise though, in general no need to cut or solder anything, power the throat only, insulate the frog, which often is insulate both rails at the frog because this is a detection block boundary anyway.
    I'm off to do some more testing - coupla things I'm not sure of, like in saying yes the classic loop trips too, that memory maaaaay have been me hand wheeling the coach back and forward over the break, rather than as the tail of a moving train. So a bit more testing, but maybe a bit more prudently after SMR Chris threatened me with the 'precious blue smoke' :eek:
     
  19. paul_l

    paul_l Staff Member Administrator

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    Ah, check the coach wheels back to back, it may be shorting out on the other blade as it passes through

    Paul
     
  20. Splitpin

    Splitpin Full Member

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    Hi Paul. Yes I'm getting more and more suspicious that may be the case.
    Maybe you can help me a bit with that as I don't think I've ever been able to really establish whether it was good or bad. Coupla months ago I bought a '00 back to back gauge' from DCC Concepts. But no way it fits between any wheel sets I own. I'm guessing it's for track building spacing, my bad. Currently it's a shiny brass sculpture on the shelf as my model boat already has an anchor.
    I have one of those 'orrible plastic Vernier gauges that just might show a variance of 1mm but probably not less. What is the desired dimension and what sort of tolerance is OK ?. Which is more problematic - under or over ?

    I will check this back to back, but basically I'll put the coach on the back burner running schedules that don't involve the reversing loops until I've arranged some other resistance wheelsets for more testing. Current plan is a couple of guards vans with DCC Concepts tail lamp and pickups, we'll see how that goes.

    Last question. So, IF we have a back to back issue, does my 'easy' points wiring method implicitly using blade switching make the issue worse ? Would the detection and/or tolerance of the short be different if I followed the cut frog feeds and power switch the frog feed method(s) ? And effectively the double-slip (alone) is already wired that way.

    Thank you all for your assistance on this. I'm pretty convinced it comes down to this coach in particular. If it were general to the type it'd be all over the internet as an epic fail.
     

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