Case Study - Electrical

Electrically, the 6.2.1 is a fairly simple railroad. Although it is possible to simply connect up the red & brown wires to the 8590 terminal track, doing a complete electrical installation is not a major challenge.

There are three steps in the electrical installation on the 6.2.1:

  • DC Train Power & Control
  • AC Momentary Operation - Track Switches & Uncouplers
  • AC Continuous Operation - Signal, Structure and Street Lighting

Train Power & Control

In the Märklin color-coded wiring system, Z-Scale track power is provided by the red and brown connections of the power supply. The track voltage in Z-Scale is 0 - 8 volts, Direct Current.

The 6.2.1 railroad is meant to operate two locomotives.  In the perspective view (above), you can see a pair of VT98 rail buses waiting at the station, while a Class 80 steam locomotive switches the mineral industry siding in the top corner of the view.  These two powered locomotives and their trains are the extent which this railroad can operate.

As designed, it was meant to be operated by a conventional mini-club transformer. In the North American market, this would be provided by the earlier 6727 or the more modern 67271 (connected to 110 volt AC mains).

For such a small railroad, there is little advantage to using command control such as DCC. Yes, there is the advantage of the load compensation feature of a DCC decoder, but it would be at the expense of having to use larger locomotives to accommodate these decoders. The 6.2.1 is a small railroad and the locomotives and rolling stock should be small, too.  A large locomotive would distract the eye from the tiny scene.

Track Power

There are three “red” connections and one “brown” connection which are the track power connections, with two of the red connections being for train control purposes.

Train Control

As designed, the 6.2.1 uses a defined segment of track at the station to “park” a train while the other train is working. An 8940 semaphore is used to control this train, but, in an apparent oversight, there is not a second segment to “park” the second train.  So, I added a second segment at the upper right, making it a locomotive service area to justify the stopped train.

The 8940 semaphore is no longer available, but it still turns up on eBay and such.  It is a logical choice for train control since it has both a solenoids for operating the signal’s blade and also a set of contacts for train control. Please see Signals for details on Märklin signals.

Rather than use the 8940, I elected to use more modern signals, the 89394 and 89395.  These signals are typically used in railroad yards, but can also be found on light traffic branches such as it represented by the 6.2.1 layout.  To control them I could have used relays such as the 8945, but I chose to use the manual 8946 manual signal controller instead. Although discontinued by Märklin, they still turn up with regularity in all the usual places.

In operation, each train is controlled by the 8946, with the signal indicating whether the control segment is active or not. Each control segment was defined with insulated rail joiners on one rail. In the case of the segment along the station platform, two joiners were used and a red wire was soldered to this defined segment. This wire is then routed back to one of the 8946’s.  In the case of the locomotive siding, only one insulated joiner was necessary.

Here, a schematic of the 8946:

Once the isolated layout sections were each connected to an 8946, the red second connections were made to a 72090 distribution strip. The red wire connection of the 8590 terminal track was also connected to the 72090. A single red wire was then connected to the “Red” terminal of the layout’s power source.

The other connections of the 8946 control box control a color light signal using two blue wires and a yellow wire, which is discussed, below. The other pair of electrical connectors of the 8946 are typically not used.

The “brown” track power connection simply runs between the 8590 terminal track and the layout’s power source.

Track Switches, Uncouplers & Controls

Accessory power for the 6.2.1 railroad comes from the yellow and gray connectors of the power supply at 10 volts, Alternating Current. Track switches and remote uncouplers are “momentary” devices, being operated only briefly to affect the desired result.

The 6.2.1 has six track switches (also called “turnouts” are operated by two solenoid coils.  In addition, the 6.2.1 layout has three uncouplers, but I chose to add a fourth on the siding that is also a train control section.  For more information about solenoid operated devices, please see here.

Here, a schematic diagram of the turnout connections, using the earlier control boxes:


With the Märklin color-coded wiring system, the solenoids are powered via the yellow connection; the control wires of the solenoids are blue with either red or green plugs & sockets, which are connected to 72720 momentary control boxes. Note that the 7209 distribution strip is now the 72090.  The 72720 control box has four pairs of control buttons, so you can control four track switches.

Here, the numbered connections to the 72720 control boxes.  The turnouts are #’s 1-4; note that #4 connects to both turnouts since both need to be thrown for proper train operation.  Each uncoupler is connected to one terminal of the 72720; one is to the green connection, the second is to the red connection of the same button pair.

Also, note that I reserved button pairs 5 and 6 for future use.  At some point in the future, I might elect to use two 8945 relays to control the signals.

That is the extent of the track switch and uncoupler installation. Installation follows the Märklin color coded wiring system, with the yellow connections of all of the solenoid devices being connected to a 72090 distribution strip (left).

Additional 72090’s can be connected for additional yellow connections; note that I chose to run a short wire from one distribution strip to a second distribution strip rather than simply connect them together. More about that later.

Each track switch has two blue wires which are connected to the solenoids of the turnout. Operating one solenoid throws the track points to one position; the other solenoid throws the points to the other position.  Each track switch has a “normal” position and a “reverse” position.  The normal position for the 8563 track switch illustrated below is for the curved-right position:

The blue wire for the normal position uses green plugs, while the reverse position connection uses red plugs.  Each of these wire pairs are then connected to the control box.  Note that the mine siding has a manual turnout, so no wiring was necessary.

In a similar fashion, the uncouplers are connected to the control box, but there is only one blue wire. This is because the uncoupler mechanism normally sits down below the railheads.  When the uncoupler is operated, the mechanism is raised to its necessary height for uncoupling. When the control button is released, the mechanism returns to its normally low position.

Signal, Structure and Street Lighting

The 6.2.1’s power supply 10 volt AC tap also provides electricity for building lighting, street lights and power to illuminate the two color light signals of the controlled sidings.  These devices consume power continuously, unlike the solenoid devices (track switches, remote uncouplers), which use power momentarily.

Signal Illumination

My interpretation of the 6.2.1 railroad uses two defined segments of track to control two different locomotives. While one is in operation, the other locomotive is “parked” in one of these side tracks.  The power to these side tracks is controlled by the 8946 Manual Signal Controller.  While train control can be done simply by using one pair of the 8946’s on/off contacts, the whole idea of the 8946 is to provide additional realism through the use of color light signals.

I chose two “track block signals”, one mounted on a tall pole and the second mounted low as a “dwarf signal:

The 89395 Track Block Signal (left), indicating “Stop”.

The 89394 Track Block Signal (below), indicating “Proceed”.

These signals are typically used for low speed train operations, appropriate for branch line operation (such as the 6.2.1 railroad).  They are also commonly used in freight yards. Other color light signals could also be used, but I wanted to keep the sleepy branch line flavor of the 6.2.1’s design.

Connecting these signals to the 8946 controller is a simple matter. 

The signal has three or four wires which come out of the bottom of the signal’s mast.  The instructions call for a 4mm diameter hole, but if you don’t have access to such a drill bit, you can use a 5/32” drill bit, or even use a 1/8” bit and “wobble” the hole out just a bit. If the hole is too large, a small amount of adhesive will help.

The instructions which come with the signal point out that the connection wires have resistors which will get hot when in operation, so these wires should be fixed in place so that they do not touch other objects.

In the case of the 89394 and 89395 signals, there are three wires. Two wires are marked, one with a red sleeve and one with a yellow sleeve; these are connected to the red and green terminals of the 8946 signal controller. The third wire from the signal is unmarked, and is connected to a “gray” 72090.  A yellow wire is connected between the center terminal of the 8946 and a “yellow” 72090.

I also connected a 89390 “distant” signal to the same 8946 that controls the locomotive service siding.  This distant signal was connected on the far side of the layout, near a tunnel portal.  The placement of this signal merely “suggests” the presence of the outside world, that there is a mainline railroad connection on the far side of the tunnel.  At the same time, it also indicates the status of the short locomotive siding since the 89394 signal is placed in such a way that it is not clearly visible from the front of the railroad.

Street & Structure Lighting

I also chose to install interior lighting in most of the structures on the 6.2.1 railroad.  Initially, I had planned on using the 8950 interior lighting fixture, which uses the 8953 light bulb insert. Along the way, I discovered that Viessmann manufactures interior lights which use LED’s rather than an incandescent bulb; this means lower power consumption and long service life. There are two Viessmann lamps, the 6018 which has a bright white light and the 6017 which is a yellowish light. They are also available in packs of ten. In both cases, the color register is not the same as the light produced by an incandescent bulb, but the power consumption and reliability outweighed this issue. Viessmann has since announced a new warm white light.

The balance of the accessory lighting was street lighting, both from Märklin and from Brawa, was merely a matter of installing and connecting the wires. It should be noted that some accessory lighting uses the European standard of yellow and brown connections rather than the Märklin Z-Scale yellow and gray; the brown connections can be considered to be the same as the gray connections.

Märklin offers a series of platform lights and street light which use LED’s; there are probably manufactured for them by Viessmann.  The connections are somewhat different from the other accessory lights in that they use a thin ribbon instead of two electrical wires.  This ribbon is connected to a small circuit board that has a yellow and a gray wire, electronics and a small clip.

A small hole is bored in the layout top and the light is glued in place. I inserted the thin ribbon partially and then put a small dab of super glue afterward to avoid getting any glue on the ribbon conducting surfaces.

The end of the ribbon has two exposed conducting surfaces; these are placed against the small circuit board’s corresponding power conducting surfaces:

A small plastic clip snaps into place, holding the electric ribbon onto the circuit board. The instructions show this circuit board being held in place with a small screw, but the ones that I had used small pieces of double sided tape.

Regardless, this process looks a lot easier than it is.  I don’t usually ask for help, but it seems that this would be the right time to ask someone to hold the ribbon with a pair of tweezers while you sneak up from behind and try to get the clip, wire and circuit board all into harmonious alignment.  This process tried my patience, but, in the end, everything worked out. At this writing, the little clips seem to be holding the conducting ribbons in place.

I know that the Germans just love this sort of wiring layout:

For the Germans, an orderly layout reflects an orderly mind. Fine enough, but for a small railroad such as the 6.2.1, going to this great length seems unnecessary since there are relatively few wires, they are color coded and they have been group together in a logical order.

Oh, that I was as orderly as the Germans, but I’m not:

A Distraction

Earlier on this page, I mention connecting the yellow distribution strips with a wire rather than directly connecting them together. This was done to eliminate a problem with interior lighting that is part of a circuit that also includes solenoids (such as track switches, uncouplers and relays). One of the things that has always bothered me about model railroad wiring is that if you use the accessory tap of a transformer for all of the accessory power, an odd problem rears its head.  When you operate a solenoid device, it draws so much power that the rest of the building briefly dims.  It’s only momentary, but I view this to be a distraction.

On larger railroads, ones that have more than one transformer for train power, there is a simple solution.  One transformer operates the solenoid devices and a second transformer supplies power for the building lights. For a small, one transformer railroad such as the 6.2.1, this is not possible.  Initially, I had hoped that the LED lighting would not succumb to the dimming problem, but that was not the case. For the moment, I’ve chosen to live with this, but in the future, I plan on connecting up the building and street lighting to a separate 10 volt power supply. Doing so will simply involve disconnecting the yellow jumper wire and connecting the additional power supply to the 72090’s that distribute the lighting power.

We’re almost done:

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