Thank you very much! I am a EE (PhD) and should have thought of that, but honestly, it has been SO long since I did circuit design that I did not even think of that. I think putting a self-resettable circuit breaker on the track input to the locomotive (especially these very old post-war F3 model) is probably the right thing to do. A post-mortem on the locomotive in question showed a severally melted front motor, partially melted rear motor, although both motors still turn and may still work, and severally melted wiring between the two motors and the e-unit. Surprisingly, no melting of the single wire from the track pick-up in the front to the e-unit. I would have expected that to have either melted or become a fuse by default. But, it did not. I have the parts on order to repair it, but it is my belief that I simply was pulling to much of a load, even though all cars were maintained. Normally, for this consist, I use two powered "A" F3 units to do the grunt work, but this time, I had just finished repainting this unit and only had the one powered A out of the ABA combination.
Now, the issue will be to determine the correct sized breaker that trips when needed, but not excessively during startup and or curves. I have Fluke multimeter that can measure current and a Fluke clamp on current meter, but I am not real sure how I am going to take those measurements while the train is moving. Perhaps measuring at the transformer will be sufficient, since there a no other loads on that track other than two LED lights (in the unpowered A and the caboose). That might be sufficient to give me the "peak" current and then add a slight factor to that so that it does not randomly trip.
Thank you for the great website. I looked over it and am very impressed. You have taken a lot of time in planning and designing (apparently) before you began to lay the first boards.
Scott
Allen, TX
