Hi!
So better don't reverse the direction when in analogue operation - this will charge the capacitor with 35+ V.

How did you measure the voltage? Is it peak-to-peak or RMS?

The rectified DC value can be much higher than the RMS AC voltage.

25 V is the effective reversing voltage. The peak voltage is higher by sqrt(2), factor 1.41. The capacitor will be charged with the peak voltage.

Try this with a 50 V capacitor (or 35 V), a diode and your multimeter.

Or set the track voltage to e.g. 16 V and measure the voltage you get in your capacitor.

Flickering lights is either caused by weak slider contact to the third rail or weak contact to the ground (wheel) contacts. This can be avoided by having return contacts on both bogies and by using a single slider and current conducting couplings. Most often, the use of contacts on both bogies will minimize this issue. If you want to do electronic modification, you can probably design a circuit that provides residual power that will allow the lights to keep burning for a few minutes after shut down, which will also serve to keep the coach lit during interruptions.
On the newest Maerklin lighting kits, one set of contacts is to be used for connections to the axle and slider and the other set is to be used for connection to the current conducting couplers. Installing a diode as shown may interfere with one or the other of those options.

Regards

Mike C

I can't answer that.
Many devices, including PC power supplies, have failed in the past years because cheap capacitors failed while being operated within the specified parameters.

It's a race condition: you exceed the nominal voltage but hope the voltage drops quickly before the capacitor gets too hot.
Could be dangerous if others, maybe children, play with your trains.

There is no guarantee the reversing voltage will be applied for fractions of a second only.
I think I would not take the risk.

Throw away the diode and connect the capacitor to where the Cx (where x is a number) label is on the pcb. 25v should be enough. You will need two capacitors per pcb. You can use smaller tantalum capacitors though.

I had a problem with flickering coach lights on my new Montreal Limited. I noticed that the long tabs extending down from the light bar assembly to current conducting base plate did not seem to contact very well with the base plate. So I put a small piece of foil between to the end of the tab and the top of the base plate. This seems to have improved the problem.
Take Care,
Steve