JohnGaltLine posted:I'm going to have to assume that you are planning on routinely running the prewar trains alongside, and on the same power districts, as the ones with modern electronics, otherwise you could simply use one output set to 18V for the modern engines and adjust a second output as needed for the prewar ones.
I can think of two solutions (well, one solution with two ways to get the desired result), neither of which is a ready made product and would require some component level electronics work. I mention this because it might scare some folks off, where as others are perfectly comfortable with "complex" solutions.
Basically what I would do is use a micro-controller to constantly read the voltage of the track in either option. from there my 'simple' solution would be to have a large load bank made with large wire-wound resistors, or perhaps car head light bulbs, that would switch on if the voltage rose over a certain point to pull it back down . The more complex option would be, rather than load down your transformer, to use a pair of triacs to regulate the output, much the same way the "chopped sine wave' is produced on most modern transformers. This gets into some somewhat complex circuits but would be the better option I think if you are only occasionally running the prewar engines.
I'd be happy to help with more specific details of how this would work if they are needed, but don't want to spend too much time on it if there is no need.
JGL
JGL: thanks for the reply. Complex doesn't scare me (or I wouldn't have started this particular project!) My first/best thought was how can I have something power a SPDT relay to switch the power through a bidirectional (for AC) diode drop with about 3 each 10 amp silicone diodes on each side when voltage exceeds 20 or 21, which would create about a 2v constant drop under load (22 to 20 volts), then when the input voltage gets down to 20v or less the relay goes back to the NC terminals and feeds 22v again. It's what could I use to trip the relay coil that stumped me. Does your idea provide a way?
Don
