HI all,
I recently completed a home made wireless controlled transfer table project and in the process I used a number of different sized LEDs in the panel on my control board. I have powered the whole project directly from my track power ( Ecos in my case) so I wanted to keep the current draw as low as possible.

Most of the LEDs were driven via a small series resistor as usual which makes for simplicity but has the drawback of flicker, worse in your peripheral vision and more so on video. So I wanted to make a small easily constructed device to stop the flicker. I have used a bridge rectifier for some years but they have been a little bulky. Recently small 800 mA SMD versions are easily available and are a lot easier to hide but a little more tricky to solder.



Both these are simply mounted on their back with double sided sticky and their feet in the air.They are wired like so.

The capacitor is not really needed for a normal LED but if you want to use a flashing type it will be necessary, otherwise the LED simply stays lit. Note the capacitor is mounted directly across the LED and need only be a low voltage type as the voltage drop is about 1.5-2 volts. More LEDs can be mounted in SERIES but the voltage rating of the capacitor needed is then higher as more voltage appears across the LEDs. I drove five LEDs happily. Simpler to use capacitors with 16 volt rating for all scenarios.
Another approach I felt was neater and could be constructed on the work bench then transferred to under the track or wherever is shown below.



Note here the capacitor is wired across the LED and series resistor. It needs to be 16 volt rated at least. The three versions are my attempt to reduce the package to the smallest footprint. Brown and yellow wires to stud and track, red and black to LED. A single series resistor is OK even with 5 LEDS in series.A few more photos.


This is all that is required for the smallest version.


[Much neater than directly soldering to the track underside.



In this case the LED is an occupancy detector and the LED return is connected to the short piece of isolated rail nearby.

This type of device is small enough for carriages, wagons, locos and under track where LEDs would be useful
Low key electronics but could be useful?
Cheers,
Howard.

Hi, Howard,
Thanks for your effort.
IMHO 16 V is on the risky side (with CU 6021 the track voltage will be around 22 V).
For digital use the capacitor should be the 25 V type to be on the safe side. For analogue use, the 35 V type will probably be enough for grey transformers, a 50 V type will be on the safe side.

It should be noted that the resistor may draw more than 0.25 W if you want to have a single, bright LED.

Aaahhh it's me again!
I have reviewed this post and the very valid comments made and it is apparent to me that I made an omission in the first posting which was not to state the circuits were designed around my setup of Ecos set at 18.8 volts. I forgot that other users could have their supply set higher and I don't know what the Marklin CS actually puts out.
This being the case please take note of the above discussion and Tom's valid comment on 25 Volt rated capacitors.
I also meant to mention that five LEDs in series will drop 10 or so volts which means the resistor only has to drop a much lower voltage and consequently will not get hot ( checked on the bench).
I reiterate the design was for "digital track power" and not for analogue as voltages are quite different.
Thank you and I hope this makes things a little clearer.
Howard.

I would do one of these:

a) Power the LEDs with a separate DC power supply so that you are NOT using valuable digital current. (Unless you do not expect to expand consumption from the track and you have plenty)

b) install one bridge rectifier (or 4 Diodes) (and possible a smoothing capacitor) and use that to drive all the LEDs on the panel, each 'set' with their own resistor sized accordingly. If there is one one rectifier/smoothing circuit, it can be positioned away from the tight confines of the panel and just bring the DC power in with a wire.

ah, I now have a better understanding of what you are doing. Sounds good. I like the fire extinguisher installation next to the turntable...

BTW in one of your wiring diagrams you show two 1N4148 diodes. Why two ???

BTW2, I used to use a 0,7V voltage drop for diodes in my calculations.
The other day I measured the voltage drop and the batch of 1N4048 diodes that I have, and they only drop 0.56V

Little do I know. I think one diode will be enough in that case. The second diode reduces the voltage a bit further.

The voltage drop of a diode grows with the current. A bridge rectifier with just a digital multimeter attached will have a small voltage drop. With a light bulb attached, the voltage drop should be close to 1.4 V.

So 0.7 V per diode is a good approximation if motors or light bulbs are involved. I don't know what the voltage drop will be if an LED only just draws 1 or 2 mA.
Three white LEDs in series with 30 kOhm are still bright enough for loco headlights, the efficiency is astounding. Same for modern LEDs in red.