I have recently completed the installation of a buffer capacitor (stay alive) on my BR64 (N scale). The exact model is Fleischmann 706183, factory equipped with DCC decoder (ZIMO MX617). This loco is very small and that does not help when it comes to current pickup from the rails. Just an unpowered frog or a bit of dirt causes the train to stop, often in critical spots of the layout.
To mitigate the issue I opted to install a capacitor. That was impossible on the locomotive, witch barely had the space for the decoder. I bought 4 freight wagons at sale (for a total of 50€) and decided to use one of them as a capacitor trailer. That meant that the wagon had to be kept connected to the engine, but I had no issues regarding that.
The first step was to solder the two wires (positive and negative) to the correct pads on the decoder. Instructions are available on the ZIMO website. I used 24AWG black wires.
I drilled two holes in the back of the locomotive, where there was a provision for backlights. At the same height, I also drilled holes in the wagon.
As the capacitor, I have chosen a 2200µF/25V electrolytic one, complemented with an 80 Ohm/0.25W resistor and a diode in the charging circuit, and a 10k Ohm/0.25W resistor as a discharge feature. Once that was ready, I fitted the wagon and closed the lid.
The BR64 is much smoother especially at lower speeds. From simple tests I have determined that with that capacitor the loco is working for 0.5s after power loss, witch is almost perfect as a stay alive solution. A more powerful engine might require more capacity.
