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Reply to "railking remote lock-on item no. 50-1013."

No, it was not amps that killed the MOSFETS. More likely, you killed the TVS diode. It's voltage spikes generated from the track, train, and wiring inductance and capacitance. Each time you open circuit an inductor after passing current- that creates a several hundred volt spike.

Both FETS are IRFZ34 https://www.vishay.com/docs/91290/91290.pdf

The TVS is a 1.5KE51CA https://www.digikey.com/en/pro...QDEsAVAWgDkAREAXQF8g

Thanks to @stan2004 for this previous post.

Okay, so flyback transient situation, overvolt protection in this case, not over-current.  Brings back memories of EE school , I remember the "Current can't change instanteously in an inductor and voltage cannot change instantaneously in a capacitor" concept.

Thank you for clearing that up!  Looking into this more, there seems to be a key trade-off design between the cross-sectional area of the PN junction of the TVS and tolerance for time exposed to a transient event.  I guess there's only so much energy than can be dissipated as heat before the component can't handle it anymore.  Since this has to fit in a tiny little lock-on, makes sense why there had to be a choice not to go bigger, even though it already seems fairly large.

I am sure they didn't think about having idiots like me overload their device 23 years after it was made.

Thanks for sharing your knowledge!  I am enjoying learning about this.

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