Thanks, your real-world experience (that these relays work for trains) is really helpful. Those are exactly the relays I was talking about -- if you look at the data sheet, they are rated at 10A for resistive loads but only 3A for inductive loads (motors) at 120VAC. As I understand it, the lower rating for inductive loads is because when the relay opens the circuit the energy stored in the magnetic field in the motor coil causes a voltage spike that can fry the relay contacts. I think a TVS would protect the contacts by limiting the voltage spike from the motor, just like like the diode on the relay board protects the relay coil. And maybe it's not important in our application since the relay contacts are rated for much higher AC voltage than the <20V we're using. If you're powering a 120V AC motor you of course don't have as much headroom for voltage spikes from the motor. In any case, I will give the 10A relay modules a try.
Thanks again for all the help! I think I'm on the right track now.
