Model Structures posted:Would you please give some detail on your use of bridge rectifiers and relays (circuit diagram)? Assuming the circuit is a momentary (wheels turn it on/ no wheels turn it off) then the length of the insulated track needs to be at least one car length long??
https://ogrforum.ogaugerr.com/t...74#40004359986239674
See above post and surrounding discussion which shows both off-the-shelf modules and a DIY circuit diagram of using a relay with the insulated rail method.
And yes, at least one axle must be straddling the insulated track section so at minimum the length must be the maximum distance between axles or practically speaking one car length as you say. In practice you will get intermittent axle-to-rail contact from dirty track/wheels or perhaps a lightweight caboose that doesn't make solid contact. To that a capacitor is added to hold the relay closed for brief (say, less than 1 second) loss of axle contact. With additional circuitry, a time delay can hold the relay closed for longer - ITADs have such longer time delays to keep the relay closed for many seconds to mask intermittent triggers.
