A while back I outlined the struggle (that may have been largely in my head!) with wiring the single slip into the MPD. After some frantic reappraisal of this as the layout was being set up at Scaleforum (thanks Chris!), it was fully operational.
Given this is a further blog post on this slip, you can tell there is a but……….. In this case it was that route setting the turnout such that it was electrically correct was not intuitive. The difficulty lay in the straight through route – to set it electrically for the route through on the main required a different arrangement of the switches to that for the straight run from the loop to the MPD. This was even though the physical route setting could be exactly the same, so it become quite confusing! Not having a power district breaker meant that the layout locked down rather too frequently as a result.
Although I don’t see it myself, the guys think that one of my main operating crew has a bit of a reputation for being a moaner when things aren’t as easy as they could be…… With this in mind, it is clear that I have to do something about this to keep the peace. In addition to the use of LED route identification lights on the control panel, I have found a third way of powering the crossings on the slip. Its this
This is a frog juicer (apologies for the Americanism!) and is simply a device that detects a short-circuit when a vehicle hits the crossing. Instead of tripping out (as a power district breaker would), it swaps the polarity. This happens faster than a circuit breaker can trip or the locomotive motor react so can be relied upon to switch the crossing without any visible effect on operation.
The net impact of this is that my slip only needs to be set for the route that is being used. The crossings will not be changed by this route setting, instead as the first wheel touches each crossing it gets switched to the correct polarity.