Hi. I am hoping there is someone here that can explain something to me about three rail and track feed back. I have been having an email conversation with Peter at LDT in Germany who make excellent digital decoders etc. Somewhere in the English/German conversation I am missing a valuable piece of knowledge and its left me confused.

On his site there are two references to connecting 3 rail isolated sections. They are:-

https://www.ldt-infocent...p?id=de:ab_rm_88_n_o_3lg (this is a list of examples - one is the three rail example as a link UNDER the list and the other one is in the list under suppression diode - the fifth PDF down the list)

Here is my question - My conversation with Peter was all using C track as the already LAID track. My layout is laid, large and ballasted so no way I am pulling up track - he explains it like this (look at diagrams) :-

1. I can cut one outside rail (between track piece ends where in C track the 2 outside rails are joined) and create an isolated section.
2. I can have many of those isolated sections (say 5 for example) in a row (five pieces of set track) and I can connect all five isolated sections in series to each other - this forming one isolated section connected to ONE contact on the decoder.

I am all good at this point - but - even though these five isolated sections exist - as soon as a train hits them the wheels and axles on 3 rail trains are all conductors - so naturally the power will now flow from the wheels running on the other side (non isolated rail) to the isolated section. IS THIS CURRENT FLOW THE TRIGGER FOR THAT CONNECTED DECODER?

If it is - then what is the example with the diode all about then? Why have a diode example? (I understand the diode restricts current flowing back to the other rail (given the way its drawn in his drawing) but so what? In the first example there is no diode anyway?

Any help to unravel this will be truly appreciated so when I do understand the physics here I can get on with bringing my layout up to feed back status.

Hi Tks for the info. I am about to do the layout for Train Controller software control in conjunction with the Ecos.

OK thats great tks. Just explain to me why exactly you have these diodes and where in the circuit are they actually placed? Rgds Greg

Hi Greg,

Excellent advice from Eric.

Iam also using Traincontroller and Marklin C tracks.

If you have Traincontroller Gold you don't need to have contact tracks physically where you want the trains to stop. The software has facility to work with shifted brake and stop marker and you can add as many of these as you want in a block. E.g. one stop marker can be defined for freight trains and another for passages trains.

This is good to know in the planning stage, before you start cutting. Some users prefer to have long isolated section. The benefit here is that if a train lost a wagon it will be detected and avoid a crash. However for most users with normal sized layout I would just recommend a contact track in the beginning and in the end. For longer sections you can have one more in the middle. Also remember in Traincontroller you can put delay timers into to the indicator. E.g. Switch off after 2 seconds after the last trigger. This way you avoid flickering where a contact may go on and off due to dirty wheels. Again with these features you don't really need to make a long isolated sections.

You will need a very fine dremel disc to cut the rails else you will end up with a large gap and a big Klank, klank every time a train rolls over! Also do some test with soldering as I believe the rails are stainless steel and not sure it will be easy to solder onto (c tracks are designed with small taps underneath for soldering).

Good luck!

Brgds Lasse

Hi Greg,

The five joined track sections will be treated as one occupancy sensor.

Shame you have ballasted the C-track without the scope to be able to lift/modify the track. I see this as a limitation to get the best out of TrainController. The cost for you is you will have a lot of external wiring.

All the best with your endeavours to use TrainController you are on a big learning journey.

On my previous layout, I followed that principle. However, taking up this hobby again after 10 years, I have spent some time calibrating my (20+) engines: Using DCC features instead of Märklin-Motorola where available, exchanging old Märklin 6090 decoders, adjusting TrainController software settings etc.. Now, every engine stops within +/- 7 cm distance, using only one sensor as brake indicator (and the same sensor as "shifted" stop indicator for both directions) in TrainController. The software still reports the complete block as "occupied". On the new layout, I will now use only one sensor on line blocks, and two sensors on switchyard blocks (where train length is more challenging).

Hello Greg/All,

Having just one sensor per block I see as an economy measure and doesn't provide good practice for reliable train control. Read the manual and you will find that Mr Freiwald gives examples and suggests the best options for reliable and easy train control.

All sensing is time based so temperature, lubrication, wear and tear can all affect how well the train runs on a particular day. If the train runs slower it will be short of the required stopping position and if it runs faster it will over run the required stopping position. Having a dedicated stop sensor in heavy traffic areas is a good idea.
The weakest item in the system are Marklin point motors. If a point fails and the train enters an occupied block you can prevent a crash by having one free sensor (reverse direction stop marker) that will detect the train entering the wrong block and stop the train.

Greg as you are on a big learning curve I can only suggest you remain flexible with the number of sensors per block and be prepared to change how things are done when a problem arises. Once you start running trains with TrainController you will find observation, observation and observation will become your mantra for improving how your trains run.

Last but not least enjoy yourself.

Really great and indepth replies. Thank you all very much. I now get it. Next comes the application. (I like the idea of practicing first on the track - tks :) )

Rgds Greg

Yes but you can only detect the thing that triggers whatever solution type you use. With the isolated section S88 detection you also detect the wagons. With the other types you typically only detect the locomotive. Also if using reed stitches triggered by a magnet placed under the loco, if you offset this to one side and need to run in both directions on a line you would need two switches on the track.

Cutting track and soldering on wiring in the isolated section of rail for each area. Or drilling holes into the track bed and installing a reed switch into every detection area. And running those wires underneath. Installing an IR optical sensor along or in the track also requires installing wiring and the optical emitter/sensor. It's also a matter of you having to modify the various cars on the layout if you also need to detect them and not using isolated rail type detection. It's a matter of what type of thing to install and how much visible stuff you are fine with being added to the track work.

Tks. I do agree that a mix will work. I did buy some IR and board from Azatrax and have read how effective pointing the transmitter diagonally down tge track can cover a pretty good distance.

Yes its funny about wiring. Originally dcc was lauded as the simple wiring solution but in the end it has its own extra leyers anyway.

When travel the real train world there are so many trackside things anyway I dont worry about IR posts at all.

Tks for all your thoughts. Greg

so tell me what I am missing about the 'diode trick'....

I understand the idea that the diode allows additional grounding. As I see it however the additional grounding can only help if the s88 is NOT being triggered.

Imagine an isolated length of track 10cm long and that section is connected to the s88 in question.
Now lets run a locomotive onto that track. Lets assume it has only three axles, spaced 15mm apart.

Axle 1 crosses over to the isolated section. It bridges the non-isolated rail to the isolated rail. (This brings the s88 'high' = 'on')
Now axle 2 crosses over, it too bridges the two rails.
At this point, if either axle 1 or axle 2 lose contact with one of the running rails, then both axles are still grounded through the other axle or the non-isolated rail.
Only if both axles lose contact at the same time, and on the non-isolated side (probability of 0.25), will these two axles lose their ground contact. The third axle will still be as grounded to the same extent as with the diode installed as it has not yet reached the isolated rail. In this case the loco will still be grounded.

As you can see, the more axles that are on the isolated section the lower the probability that all axles lose contact with the ground.
Axles on the isolated section can also include non-loco axles.
Thus the longer the length of isolated rail, the less need there is to allow grounding via a diode.

If the set of axles does not bridge the two running rails then the s88 will not work at all, so adding a diode for this case may help the loco get grounded but it won't help the fact that the s88 will not get triggered. This case is the same same as not having the s88 detection point at all.

So, am I missing something if I conclude that instead of adding diodes the following will suffice:

- Keep isolated sections longer than the distance between the leading pair of axles.
- Keep the track clean

This will ensure that the s88 detection works well and the loco will obtain proper grounding.

I have never added diodes to my s88 connections and I do not have issues with locos losing ground contact.

Note that if pushing a consist with the loco at the rear, the s88 detection is achieved by the leading axles of the first car, and it does not need power to keep the train rolling, even the asinine special trains that have pickups at both ends and insist on switching between one or the other pickup depending on direction of travel.

Now if people are running wheel sets that are for DC, then those axles will not bridge the isolated rail and only the loco axles (or any AC axles) will work.

Please excuse me from butting in, but every reed switch I have tried (Maerklin or Viessmann) with C track has always caused unacceptable bumping or displacement in the sliders or wheels of the vehicles passing over it, no matter how carefully I installed it or how tightly I screwed it down.
Is there some trick to reed switch installation that I am missing?

I've seen folks install the reed switches below the plastic track bed along the line of the center conductor. Not sure what affect that has on the magnet needs.

Sure, in an ideal situation you don't need it and just have the one rail for earth. This is essentially 2 rail DC.
We have all heard reports about bad running on 2 rail DC layouts though.
I find the centre stud conducts without issue due to the self cleaning mechanism of a slider, so having 2 earthed rails and not just 1 does improve running if the rail is a bit dirty.
This is what the diode trick does when using one rail for detection, though as mentioned it is only half wave earth.

Hi Dale.

Two axle loks: Glaskasten, Köf II, Köf III, Schienenbus. Just to name a few.

Regards

Tor

Some more 4 wheel locos

E69


Wismar Railbus


Kittel railbus

I agree 100% with this..