Carriage lighting for less than €2
Notice: A friendly expert advises modifying the circuit below, especially when used for long trains with interior lighting.
When power is supplied to a long train (e.g., when turning on your layout), all capacitors are charged at once, resulting in high electric currents. To ensure a more gradual charging process, it is recommended to add a resistor between the rectifier and the capacitor. However, this adjustment will impact the brightness of the carriage lights. The optimal resistor values are still under evaluation, which is why the circuit design below has not yet been updated.
For lighting passenger carriages, pre-made LED strips are available that can be easily attached to the interior of the carriage roof. However, creating the lighting yourself is not only more cost-effective but also more rewarding. Using the components described here, you can craft a simple yet efficient lighting solution for less than 2 €. This guide is based on a digital layout, but it should also work with analogue systems. Keep in mind, for analogue setups, the brightness of the lights will correspond to the transformer settings—meaning the lights will dim or turn off as the train slows down or comes to a stop.
I used these LED strips from a Pound Store as the foundation for this project. However, feel free to use any other strips with a fixed, unchanging color (so ones that don’t come with a remote control).
If you'd like a detailed PDF guide for building this carriage lighting—complete with additional tips and important considerations—you can request it through the Contact page. Below, I’ll only provide a brief overview.
Disclaimer: The information provided below is for your reference only, and any use of it is entirely at your own risk.
I strongly recommend starting with higher resistor values, especially if you deviate from the circuit shown below, use alternative components, or have a diffrent number of LEDs. If the LEDs are too dim or do not light up at all, gradually decrease the resistor values in small increments until you achieve the desired brightness.
Additionally, it's a good idea to test the lighting setup outside the carriage first to ensure none of the components overheat. After all, you wouldn't want the roof of your valuable model carriage to melt!
Circuit for carriage Lights
The primary circuit for the carriage lights is shown alongside in black. The grey section illustrates an optional extension for tail lights (details provided below).
At the bottom, you'll find the power feed, which provides a variable square wave pattern (often mistaken for 'alternating current') coming from the wheels. I recommend adding a switch (S) here to give you the option to turn off the carriage lighting. Without a switch, the lights will remain on continuously since a digital layout is always powered. However, adding a switch is optional if you prefer to keep things simpler.
Since LEDs do not withstand alternating current (AC) well, the power from the rails is first passed through a bridge rectifier (bridge cell B) to convert it into a sot of 'direct current '(DC). Any bridge rectifier rated for at least 24V will do.
Between the positive (+) and negative (-) terminals of the bridge rectifier, we install an electrolytic capacitor (commonly referred to as an "elco") with a minimum rating of 220μF and 24V. However, if space allows, it's recommended to use a 470μF and 35V capacitor, as a higher capacitance will yield better performance. Due to the bridge rectifier, the voltage rises considerably higher than the 16V supplied by the power source.
An elco ensures stable lighting by preventing flickering caused by poor rail contact. Acting as a buffer, it temporarily stores energy and instantly releases it when the power supply from the rails becomes unstable.
Caution: When mounting a capacitor, always ensure the positive terminal of the elco is connected to the positive side of the bridge rectifier, and the negative terminal to the negative side (refer to the circuit diagram above). An improperly installed capacitor can cause an explosion and/or a fire!
The final component in the circuit is the 4.7kΩ (kilo-ohm) resistor. This resistor is essential because LED strips cannot handle the high voltage output from the rectifier. The exact value of the resistor depends on the number of LEDs in the circuit and their configuration (series or parallel). In my setup, which consists of 2 series of 7 parallel LEDs, I determined through experimentation that a 4.7kΩ resistor works best. However, using a slightly lower value is also an option—it will cause the LEDs to shine a bit brighter. It doesn't matter whether you install the resistor on the positive or negative side of the circuit; the key is to ensure it is connected in series with the LED strips.
As illustrated in the image, I solder the components onto a small piece of circuit board. This simplifies installation within a carriage. Before installing the bridge cell, ensure you cut the copper strips on the board as indicated by the small arrows. (Note: the strip in the middle is not used.) Again, pay close attention to the correct polarity of the elco; the negative side is generally marked. To prevent short circuits, it is highly recommended to wrap the circuit board in insulating tape or standard cellotape before securing it inside the carriage.
Tail Lights
In the diagram above, a few additional components are shown in grey. This part is optional; I only install tail lights on the last carriage. These are the two red 'rear lights' that mark the end of a train.
The 3mm red LEDs can only handle a maximum voltage of 1,8V. To ensure proper operation, an additional 10 kΩ resistor is required in combination with the standard 4,7 kΩ resistor used for the carriage lighting. These two resistors must be connected in series. It's important to note that the power supply for the carriage lighting is connected between the two resistors. This ensures that the LED strips receive power only through the 4,7 kΩ resistor. If you were to connect the LED strips directly at the top of the circuit, the total resistance (14.7 kΩ) would be excessively high, preventing the LED strips from lighting up.
Wiring to the wheels
Begin by verifying that the wheel axes are installed correctly. The insulation on the wheels (highlighted in the photo with a red line) must be positioned on opposite sides at each end of the carriage. This ensures that one wire of the lighting system connects to one rail, while the other wire connects to the opposite rail.
Connect the feeder wires from the print to the collector shoe of the wheels when present (shown on the left). Alternatively, you can create your own connection by loosely wrapping a thin, uninsulated copper wire around the carriage axle a few times, as shown on the right. The photo also shows switch S, which can be used to turn off the lighting. Personally, I like using the sliding switch from the original LED strip battery pack for this purpose.
Mounting the LED strips
If your carriage has plastic roofs, it’s recommended to first attach a lightproof material such as aluminum tape, to the interior surface. This helps enhance the lighting effect and prevents any light leakage.
In my case, the LEDs on the strips were spaced quite far apart, so I glued two strips side by side as shown in the photo. This ensured that each compartment in the train received illumination from at least one LED. Keep in mind that many LED strips have adhesive backing that doesn’t stick well. So it’s a good idea to reinforce them with all-purpose glue.
Additionally, make sure to insulate the aluminum tape with non-conductive tape in areas where you’ve soldered connections. This will help prevent short circuits. Of course extra caution should be taken when working with metal carriage roofs.
Result
Place some figurines inside the train. Then carefully close the roof, ensuring that no wires are visible through the windows. The result is a beautifully illuminated carriage. The masked windows between the 2nd and 1st class sections conceal the printboard almost completely unnoticed.
