Actually, I like the idea of running the fan slow, then hitting it with a shot for the chuff, that might eliminate the issue of it overheating. The output of the R2LC is not full 18 volts, it's actually half-wave. When you apply the boost, you get the full wave output voltage, but I don't believe that's 18V either. FWIW, the smoke unit in this PS/1 locomotive is connected directly to track power, so it's getting whatever it takes to move the locomotive and cars.
Got the schematic for the PS/1 smoke unit, it's more complicated than it would appear. The smoke resistors are in series, and they have a voltage switch to bypass to a single one when the voltage goes low, I guess to keep the smoke output up at slow speed by heating it hotter.
I had no idea how to find the service note you mention over at MTH, not the best designed site on the planet. 
