I decided to rewire so all the bridge power comes from the same power block at one end of the bridge. It requires more contacts so that I still get a dead rail at both ends when the bridge is out, but sounds electrically safer. I will post "Bridge Out" warning signs in the middle of the tracks when the lift out is open. Thanks Randy:
Capt. Brigg FranklinUSCG Licensed Marine OfficerCertified crazy train chaserCEO: Pacific Cascade Railway
Yeah don't do that, that could be potentially bad if something went wrong. It's actually possible to have double the voltage across the loco if things fail in a specific way. Wither cut it in half like I mentioned, or make the entire bridge all in one district. The approach contacts don;t have to electrically connect to the bridge rails, it can be as simple as a microswitch that is closed when the bridge is locked down, so the one apprach could be wired to cut off when the bridge is raised, yet not actually supply power to the bridge rails.
Cutting off the approach power is a reasonable sanity check - as long as all trains are moving forward. If one is backing and someone doesn't see that the bridge is out, it will shove half the train to the floor before the power hits the dead section. A physical barrier that pops up is the ultimate big wrech preventer - it may derail cars and pop a few couplers but it's less damage than a fall to the floor. Do both to keep locos from slamming full speed into the barrier, and protect the non-powered end of the train from the fall into the grand canyon.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy,
Thanks for responding. What I am proposing is one of the two bridge rails (all of it) is in one sub-district from the right side of the bridge and the other bridge rail (all of it) is in another sub-district from the left side of the bridge. The only gaps are at the ends of the bridge. That way an engine on the bridge will be getting power from two sub-districts. This will also happen when an engine crosses over a gap between two sub-districts and the pickup wheels are on both sides.
Yeah mean like split the bridge in the middle so when it's allin place, half gets it's power fromt he right arm of the U, and half gets its power from the left arm of the U? That will work just fine. In that sense, it's just like having multiple power districts around a complete donut, just with some extra gaps and jumpers to de-power the approach tracks. That's all you should need to go - gap the middle of the bridge, if you do not do that, then the bridge will also electrically bridge between two sections of the PM42, and it won;t work.
I have three power sub-districts and a reversing section using a Digitrax PM42. I also have a 24" lift out bridge for access to the center of a "U" shaped layout, and each arm of the "U" is a separate sub-district. I want to wire the bridge rails separately from each end of the lift out bridge, with a make or break contact, so that a short section of the approach rail goes dead when the bridge is lifted out. This requires that the bridge rails each have separately received their power from different sub-districts of the PM42. I am wondering is this "mix" of power sub-districts on the bridge will result in a short not being recognized by the PM42 or that the DB150 Command Station will see the short circuit? If this creates a big problem, I'll run a wire around the layout from the first sub-district so the bridge rails are all from the same sub-district. Suggestions, ideas? Thanks