First digital operation…

Okay, it was a simple but oh so vital test with a couple of locos. Nonetheless, the first ‘trains’ ran yesterday, up and down the yard reception roads. Digitrax is the chosen digital system for my MRL 4th Sub project and the Super Chief base station together with a PM42 Power Management Module were installed. Power is supplied from an On Tracks 5amp transformer.

In case you are wondering what a PM42 is going to do for the layout, here’s an explanation. It’s an add-on device which manages power distribution around the layout. It has four circuits and four circuit breakers. The track (power) bus is connected in one end (actually you split it into 4 and connect to four pairs of terminals in the connector, one for Rail A and one for Rail B). The output is four separate runs of track bus cable which powers four ‘sub-power’ districts (the running line rails are double gapped where it crosses from one sub-power district into the next in the same manner as power districts are separated from each other). Each is independent of the others and if a short occurs in any one sub-district, the circuit trips leaving the remaining three unaffected. Short circuit detection is intercepted by the PM42 before it reaches the base station booster. This has obvious operating benefits although, unlike providing additional power districts using additional boosters and power supplies, there is no extra power made available.

Definitely blows the two-wire myth of DCC right out of the window but it is a two-wire supply of power to each sub power district one red and the other is black. The wiring consists of the power in and four pairs out together with a power supply for the PM42 and a single earth to the command station (yellow). What really interests me in the PM42 is that they can have one or all of the circuits programmed to provide the required polarity switching for reverse loops, such as the two I have in my layout plans. I allocated two circuits to reverse loop management and the remainder to manage two sub-power districts. I may need more as the project develops, but this is sufficient for Phase 1 of the layout.

The blue edge connector on the PM42 was wired on the work bench and then assembled on top of the baseboard like this for testing and programming through OPS Switching. Once working reliably, which took no time at all, everything was installed in the layout.

That looks a great deal neater. The base station is located in the balloon track seen in previous pictures so it can be reached easily. The programming track will also occupy this space too. Two wiring runs are routed to the upper deck and the other two run under the lower deck baseboards. Note the labelling over the PM42 which was mounted on the wall out of harm’s way but where indicator LEDs can be clearly seen (Note that all cable runs should be clearly labelled and cable colours for Rail A together with Rail B clearly identified).

The DT400 throttle was connected directly to the command station for testing the circuits as seen. With this work complete and functioning correctly, the track bus was installed under the baseboards and throttle (cab) bus faceplates together with the correct cabling prepared for fitting to the front of the layout. With that, it’s back to track!


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