PLCProf posted:...I'm guessing that the DC supplies were intended to permit the use of 12 VDC sense relays, but the filter caps in the supplies caused the sense relays to hold in for a while after the power was lost, so the 8.x volt setting was chosen to put the relays right on the edge of dropout to speed up the response to a power loss.
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Just talking........
Agreed. We are just talking. 
So if these are indeed the LY series relays, note that for the 12V DC version it Must Operate at 9.6V and Must Release at 1.2V. I think that would be walking quite the fine line (i.e., delicate balancing act) to trim the DC voltage to 8.7V, or 8.8V, or 8.9V, whatever to drive a 12V DC coil that will hold until the capacitor drops to what could be as low as 1.2V!
Practically speaking, other than ASAP, how quickly must a safety system respond to one brick tripping? Given momentum, if you instantly remove power the consist might nevertheless coast several car lengths...and of course the prototypes much further without dynamic braking. So for a model train setup, I'd think maybe 1 second is a reasonable goal? That is, consider a human operator visually watching. A derailment is detected. Now, in a panic, find the E-stop button on the remote fob which was supposed to be hanging on your neck but in all likelihood left somewhere because you had meant to change the battery! 
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