Riggenthalerbahn - Technique (E)

Technique

Summary
Basic Principles	Traction Current	Walkaround	Distribution
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Basic Principles

- HO scale (1/87)
- Basically 2 rail DC
- Functional catenary (For a layout located in Switzerland, the question does not even arise!)
- Analog control (No digital)

Traction Current

My collection of motive power is absolutely heterogeneous, in other words, there is really ... everything!

- Steam or diesel engines 2 rails DC (taking the current through the rails)
- Electric engines 2 rails DC (can also take the current by the catenary)
- Engines 3 rails AC (Märklin system, taking power only through the catenary)

And if possible, I would like to be able to drive all that on my layout... DC and AC on the same track? Of course it's possible! You just need the transformers for both systems, plus some wiring:

2 rails DC	3 rails AC

The transformer T1 (Track) is connected to the 2 rails, and the transformer T2 is connected to the catenary and to one of the rails (defined as the common rail to the two transformers). This allows independent control of 2 locomotives on the same section of track.	The transformer is connected to the 2 rails (in short-circuit) and the catenary.

	To switch between the2 systems, it needs:
	2 rails DC	3 rails AC
Rail 1	DC Transformer T1 (V)	Ground
Rail 2 (Common)	Ground	Ground
Catenary	DC Transformer T2 (C)	AC Transformer T3 (C)
	For the rest, I will use the abbreviations M ("Masse" in french, ground or common rail), V ("Voie" in french, the other rail) and C (Catenary)

The common rail 2 (M) is always connected to the ground, which is common to the 3 transformers. The rail 1 (V) is connected either to the DC transformer T1 or to the ground, and the catenary (C) is connected to either the DC transformer T2 or AC transformer T3. The whole thing can be done with a simple "CC/CA" switch:

Another possibility: Add a switch "C<>V" to switch the DC transformers T1 and T2 (The reason I added this will become obvious in the next chapter "Walkaround" ...)

Last addition: A switch "C=V" for powering track and catenary with the same DC transformer (T2 or T2, depending on the position of the switch C<>V). This makes it possible to ensure a good power supply for the machines having a doubtful current collection, but equipped with a pantograph (Example: The small shunter Te 101 of Hag), but also allows double heading with one of the locomotives taking by the rails and the other by the catenary: The 2nd locomotive can dock the 1st, then by switching the switch C=V, both are controlled by the same transformer.

The final result is that it is possible to drive both "2 rails DC" and "3 rails AC" (Märklin system) engines. The only condition for 3-rail trains to be able to run is that there is at least one pantograph on the train, which is even not necessarily located on the locomotive! For diesel or steam locomotives, it is sufficient, for example, to include in the train a Swiss or German restaurant car equipped with a pantograph, and to connect it electrically to the center rail contact shoe of the locomotive.

Only modification to be made on the 3 rails engines: Remove the contact shoes of the 3rd rail (which otherwise will hang in the points). AC (uninsulated) axles do not need to be replaced by isolated axles, but wagons equipped with uninsulated axles can only be operated with locomotives that also operate in 3-rail AC system.

Walkaround

A "Walkaround" is a small hand-held traction current regulator, allowing to move around the network while driving the trains. I happened to find one of these "walkarounds" during a trip to England, a (very) long time ago!

This little regulator not only has the advantage of being handheld (therefore, no need to sit in front of his stationary transformer to drive!), but also offers a very fine trimming of the traction current. Many of my locomotives run much better with this walkaround than with a traditional transformer. I use it as a DC transformer T2, with the possibility to supply either the track or the catenary via the switch C<>V (see diagram above). It is supplied with 14V AC power, and can be connected to 4-pin DIN sockets distributed in different parts of the layout.

Distribution

Now that we have our 3 cables M, V and C, it is a question of distributing the current on the layout. Given the dimensions (about 30m track lenght!), I decided to use strong section conductors to avoid line voltage losses. As in addition the layout is modular (= demontable, some of the modules have already survived 3 moves!), it is desirable that the connections between modules are easily demontable too. The idea came to me on one of my previous jobs: 6-core cables of 1mm2 Cu with corresponding connectors, used under 600V. All this allows me to make a power supply that goes around the entire layout, distributing traction current and 14V current for accessories on each module.

1- M ("Masse", traction ground)
2- V ("Voie", Rail)
3- C (Catenary)
4- T2 (DC Transformer T2 "Walkaround")
5- 14V accessories
6- Ground 14V

Each module is equipped with a splitter (a simple bar of 12-pole dominoes) ensuring the connection with the next module and to "stitch" the current everywhere necessary.

The four cores M, T2, 14V ~ and 14V ~ M allow to install sockets wherever it will be necessary for the connection of the walkaround.

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