Greg,A basic understanding of electronics is needed before making some of the statements you have both made.
First: faulty circuit breaker: that Bridgewerks will deliver 15 amps all day. If you have a SITUATION where you are drawing 15 amps, it will go on FOREVER and the circuit breaker will not trip, and well it should not.
If you manage to put the loco in a SITUATION where it DRAWS 15 amps, you will indeed destroy something.
The lack of understanding here is how to make the SITUATION where you can DRAW 15 amps. Clearly with the wheels turning, it was not drawing 15 amps, 15 amps going through that motor would destroy stuff. So there is NOTHING wrong with the circuit breaker.
Current is drawn in proportion to the voltage and resistance in the circuit. Please read about Ohms Law.
So, in the NORMAL SITUATION, the motor's resistance is such that it will only DRAW about 1 ampere... so no damage will occur. (you could have a 1 million ampere supply and this would still be the same)
Now, if the VOLTAGE from the Bridgewerks suddenly went almost triple, that would triple the current, i.e. the locomotive would DRAW more amps, and this could damage it.
locking or impeding the drive train will reduce the resistance of the motor and then it will DRAW more amperage, and that is a common mode of damage, BUT you say the wheels were turning... (this part of the story does not compute)
a SHORT CIRCUIT, i.e. bypassing the motor (the circuit becomes shorter) would DRAW a lot of current, and normally exceed the 15 amp rating and then the circuit breaker would trip, BUT you say the wheels were turning, so there was NO short circuit.
Again, the story still does not "jive" with what happened... it the loco was mechanically stalled or "binding" the story would make sense, or a short circuit somewhere... BUT if the loco derailed and the wheels were turning it cannot be..
Is there any chance that the wheels were turning, but really slowly and binding? This is about the only guess I can make where you could draw a lot more current to cause the motor / brushes to be damaged.
Really appreciate your explanation and with you explaining Ohms Law, it makes sense that the engine would only draw current in proportion to the voltage and resistance in the circuit.
The question then becomes, what caused the engine to pull up to 15 amps because if it pulled more, the circuit breaker on the Bridgewerks would have tripped but since it was not tripped
the amps did not exceed 15 but that would destroy stuff like the motor and gears. Engine had a strong burnt smell.
The wheels were turning but slowly so I think you have pinpointed the problem. The drive train was impeded during the derailment reducing the resistance of the motor which caused it to draw
more amperage which could have gone up to 15 amps with my Bridgewerks which would have caused the motor and gears to burn out.
With the problem probably identified in that it was not a short circuit and that it doesn't matter how big a transformer I have because of Ohms Law, it sounds like Pete had a great suggestion when
he suggested I put a 3 amp polyswitch in one leg of the connectors between the transformer and track. This would pop at 3 amps and save the motor from burning out because of the extra amps the engine is calling for because of the binding of the wheels or impending the drive train.
Does that make sense?