What are the advantages of using 2 wire block wiring from the control panel DPDT switch over common rail wiring on a straight DC HO layout as it relates to train control, signaling and future part DCC control (part DC part DCC)at a later date? Thanks
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subman What are the advantages of using 2 wire block wiring from the control panel DPDT switch over common rail wiring on a straight DC HO layout as it relates to train control, signaling and future part DCC control (part DC part DCC)at a later date? Thanks
I have always used a two rail block sytem because it is really a must if you want signalling. I just have two cabs and use a DPDT center off toggle for block selection. One can hook to all of the A pair and the other to the B pair. Using that method one can line up a series of blocks for a route rather than have to turn a rotary selector switch as the train advances.
If you want to operate in DCC you need only connect it to the A side and instead of the A cab and you can then select either DC or DCC operation.
I use 2 rail block because it's somewhat difficult to feed + to the common rail of a block when it's being charged with - in the very next block. Been there and done that.
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I have been using common rail for analog DC control for a long time - better than half a century - and there is one key to making it work (or fail to work, if this is ignored):
Every train must be controlled from its own, totally independent power supply!
By independent, I mean no common connection to ANYTHING between the 120vac line cord and the reverse switch that controls locomotive direction. NO two throttles on one power pack, unless each has its own, totally independent transformer winding.
Also, while the common rail is all connected to a single bus (sort of anticipating DCC wiring!) it is good practice to gap that rail, and arrange drops that can be disconnected for troubleshooting.
In analog DC wiring, common rail just about halves the amount of control wiring and the number of contacts on panel switches, simplifying the wiring and reducing the cost. This may not mean much on a simple layout with four electrical blocks. It's a credit rating saver when the layout's electrical blocks are counted in the hundreds.
(How MZL shrinks that down to a manageable number of power selectors is another, very long, story that I don't intend to tell here.)
Chuck (Modeling Central Japan in September, 1964 - analog DC, MZL, common rail)
Chuck,
MZL, as in Master, Zone, Layout control by Ed Ravenscroft? Great stuff, I use a similar system partially based on his work.
To the orignal poster, there can be some other andvantages to not using common rail, but they depend on the throttles and other equipment you are using. Just like explaining MZL, explaining reasons for not using common rail would take a small book. When I finish mine, I'll let you know. But both aproaches have merit.
Chuck's advice about throttles applies to all DC layouts for good performance and design.
Sheldon
The major problem for common rail in DCC is if you have more than one booster. You can potentially get a differential of double the track voltage across a gap in the not-common rail.
For a small layout with no extra boosters, it matters no one whit if you use common rail or gap both. I've always gapped both, even with DC, and never used common rail. DPDT toggles for DC with both rails gapped cost only a few cents more than SPDT - if you have hundreds of blocks it matters cost wise, but for smaller layouts - no big deal. I've always double gapped my blocks in DC and so switching to DCC there was no change in the way I laid the track, other then that there were far fewer gaps.
For a larger DCC layotu with signalling and detection, you really end up with a series of common rail sections. Most detectors only connect into one side of the track power wiring. Say your detection block is 12 feet long, and you follow the rule of thumb of a track feeder ever 3 feet. So you have gap----feed---feed---feed---gap. The detector hooks to one side of all 3 feeders. The other three go straight to the main power bus. In essence - a 12 foot long section with common rail wiring. Each detection section is double gapped from every other detection section, but within the detection section, you end up with common rail wiring. Even if you don't add signalling right away you can plan ahead by making two track busses, one tied to the track feeders and one tied to the DCC system, with jumpers between the two. When you gap the rails for detection later, also 'gap' the bus that's attached to the rail feeders. The detectors themselves get wired into the 'jumpers'.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
The biggest advantages of common rail wiring is that it's simpler and cheaper. Now any time you get simpler and cheaper this hobby, there has to be a trade off. With common rail and DC you lose the ability to have two trains running in opposite directions in different blocks at the same time. You can do it if one of the trains is completely stopped. That's because to do that with DC requires making the wire that's positive on one block negative on the other block which can't be done without doing some extra special wiring.
So if special wiring is needed to do the above, then just wire it that way in the first place and be done with it. 2 wires and DPDT block switches will allow more options and make trouble shooting much simpler.
OK, more on the advantages of not using common rail.
If you: Gap both rails, stagger those rail gaps 12” to 18”, double switch your cab wiring using no common bus and use separate power supplies for each cab, you make it impossible for trains to over run their territory. When two adjacent sections are assigned to different cabs the area of the staggered rail joints will be a dead zone because any loco will only be on one rail powered by its power supply and the other power supply is isolated from it.
When both sections are assigned to the same cab the loco sees its power supply the whole time and travels right through. No more “who’s got my train” and no more loosing control, if the proper sections are not selected, the train just stops.
If you extend this idea to X-sections or “floating blocks” as some call them, creating this same staggered powering by connecting one rail to the east and the other to the west for the route selected, then you extend this protection to interlocks, crossovers, sidings, etc. Again this makes it impossible to over run your assigned sections.
Add to this wireless radio throttles and the ability to assign a cab to a given section from more than one location and you have complete walk around flexibility with DC.
mfm37...With common rail and DC you lose the ability to have two trains running in opposite directions in different blocks at the same time. You can do it if one of the trains is completely stopped. That's because to do that with DC requires making the wire that's positive on one block negative on the other block which can't be done without doing some extra special wiring...
ATLANTIC CENTRAL OK, more on the advantages of not using common rail. If you: Gap both rails, stagger those rail gaps 12” to 18”, double switch your cab wiring using no common bus and use separate power supplies for each cab, you make it impossible for trains to over run their territory. When two adjacent sections are assigned to different cabs the area of the staggered rail joints will be a dead zone because any loco will only be on one rail powered by its power supply and the other power supply is isolated from it. When both sections are assigned to the same cab the loco sees its power supply the whole time and travels right through. No more “who’s got my train” and no more loosing control, if the proper sections are not selected, the train just stops. If you extend this idea to X-sections or “floating blocks” as some call them, creating this same staggered powering by connecting one rail to the east and the other to the west for the route selected, then you extend this protection to interlocks, crossovers, sidings, etc. Again this makes it impossible to over run your assigned sections. Add to this wireless radio throttles and the ability to assign a cab to a given section from more than one location and you have complete walk around flexibility with DC. Sheldon
I like that idea. If I have a single cross over between a double track line where would the gaps be to create a "floating" block?
Russell,
It is much easier to understand in a drawing than in words. This will be covered in the info I am sending you as a result of our prior conversation. It should be off to you in a day or two.
It seems to me that gapping both rails to create blocks is more straightforward, especially since you have a couple of reversing blocks. The dollar amount saved in wire and switch contacts on a small-to-medium sized layout is negligible and I've found (personally) that having both rails gapped makes for easier troubleshooting. Both can work, but particularly if you are thinking of having both DC and DCC at the same time at some future date, gapping both rails now could save headaches (and toasted gear) later.
Byron
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