I recently added a K-Line SW-2 diesel for my 1950s Marx layout that I have had since I was a kid. In sharing this information elsewhere, I was advise that I was risking frying the engine circuit board with a short without a surge protection between the transformer, an AF 75 watt with working circuit breaker. I contacted the recommended seller who agreed.
I also add last year a FlyerChief diesel for my AF layout that is powered by an AF 100 watt transformer. Contacting the Lionel store, I received two different answers to the same question, referring to the Lionel engine. One was definite- any short is to be avoided. The other said the circuit breaker in the transformer is sufficient.
Both engines have experience shorts, especially the FlyerChief. Both layouts are small. Marx would fit under the bed, the S scale 5 x 9. Would appreciate any feedback or experience with this problem.
Bob
Hi Bob, welcome to the forum. Sorry for the delay in replying to your questions.
There are two different issues to be addressed with your request for help. Voltage and current.
Voltage spikes are usually caused on a model railroad layout by derailments and the collapsing magnetic fields in the coil windings of transformers, motors and electromagnets when the voltage is abruptly interrupted. Such voltage spikes can damage the sensitive electronics in FlyerChief locomotives and other command control devices. Voltage spikes can be protected against by installing TVS (Transient Voltage Suppression) diodes in parallel with each transformer's outputs. One or two additional TVS diodes distributed around the layout, with one lead of each connected to one track rail and the other lead connected to the opposite rail.
With regards to current (measured in Amps) the circuit breakers built into the transformers are designed to prevent the transformer from delivering so much current that it's windings overheat and melt the insulation between them. This built-in circuit protection is sometimes insufficient to protect the wire insulation and circuitry inside locomotives and powered train cars from melting in the event of a derailment where one set of wheels comes into contact with the opposite rail. This type of derailment is fairly common in O gauge 3-rail, but may or may not be as common with 2 rail S gauge. If you want to protect against this condition, installing some inline fast acting (sometimes called fast blow) fuses rated for somewhere in the neighborhood of 3 - 5 amps (either 125 or 250Volt rating) would be fine. You may want to experiment a little with which fuse amperage rating works best for your applications so that the fuses only blow when a short across the rails occurs, but doesn't blow under normal operating conditions.
