Model Railways

G Scale Coach Lighting

I have decided to put lights in 3 of my LGB passenger cars or rather ask Robert one of my sons, to do it for me.

Robert explained that it wasn't as easy as I thought it would be, certainly once Robert had worked on a 'wiring' diagram I realised just how complex this easy task was…..

The Technical Details First:

I have both analogue and digital G scale locomotives and use an LGB MTS (multi train system) control with a Massoth remote controller, this can be set to either analogue or digital as required. For more information see HERE

The digital system is AC with the voltage from the track to the locomotive remaining constant. In the case of the analogue system there is only DC from the track, and the voltage is variable, set by the controller. I want the coaches to be lit on either system and also forward and reverse, not as simple as I thought that it would be, but what do I know. Fortunately for me Robert has all the necessary qualifications needed to do the work, and many more.

Each coach needs the following components:

Included in the photograph are the plastic wheels that I am replacing. I think that they do look better than the replacement wheels but unfortunately are not suitable.

2 sets of LGB ball bearing wheels

The LGB ball bearings wheels help decrease friction, they include built-in electrical pickups for easy wiring of lights and accessories in coaches and come with crimp-on connectors, but these won't be used the connection will be made by soldering the wires direct to the pickups

10 Constant, LEDs: Size: 3mm, colour: Warm White.

These require a fixed voltage of 2.9 volts. Any more and they can be damaged or have lifespan shortened. Too little voltage and they will not light at all.

4 x 1A Silicon Rectifier Diodes

A rectifier is a type of diode that converts alternating current (AC) into direct current (DC). An alternative use is for polarity protection of positive and negative track rails providing the power to the coaches. The diodes perform both of these functions as they are used for AC and DC locomotives.

Diodes only allow current to flow in one direction, and they're always polarized. A diode has two terminals. The positive side is called the anode, and the negative one is called the cathode.

The diodes are used in the case for the (AC) digital signal controlled layout as this operates on an AC voltage and then provides the correct DC polarity to the coaches.

In summary, the diodes change the digital AC to DC, then ensure the circuit has the correct polarity. In the DC analogue system, the diodes only provide the function of correct circuit polarity.

1 x Adjustable Voltage Regulator (DC Step down buck converter)

Adjustable voltage regulator circuit maintains a fixed voltage output. This guarantees that no matter the fluctuation in voltage, the voltage driven to the LED will be maintained at the specified level. In my coaches the output level needs to be set to 2.6 volts

The voltage regulator regulates the higher track voltage down to a fixed low voltage output to protect the LED's. A voltage regulator maintains a constant output voltage for a circuit, regardless of any changes in connected devices or electrical load as long as its input is a couple of volts greater than the required output

Radial Capacitor 105C

An electrolytic capacitor is a polarized capacitor which uses an electrolyte to achieve a larger capacitance than other capacitor types. The word “radial” refers to the lead configuration. Both leads exit the capacitor from the same side.

In my circuit it is used to store some brief energy, similar to a rechargeable battery to maintain constant illumination of the LEDs. The capacitor helps to maintain the illumination if any brief connection of the coach to the track is lost, for example local oxidisation of the track or across track joints. If the capacitor has to use any of its stored energy, it will quickly recharge when the coach receives good electrical connection again.

To prevent any damage it is vital this component is fitted correctly and also allowed to fully discharge before carrying out any works on the coach electrical circuits because of the energy it can store,

A basic wiring plan:1,new wheels - 2,diodes - 3,capacitor - 4,voltage regulator - 5.LED assembly.

The full wiring plan in detail, click to enlarge.

Step by step photographs of the works completed.

The coaches are LGB 31400 DR-Personenwagen 901-203. I will use the term coaches throughout this article but cars and carriages are also OK.

To show that I do things occasionally I have fitted the new wheels.

As you can see both wheels have pins on them but Robert will only be using 1 set, The other set can be used for anything else that I might want to add to the coaches that draw power from the track.