DC-wired track logic issues

Discussion in 'HO Scale Model Trains' started by Santa Fe Jack, Jan 5, 2007.

  1. Santa Fe Jack

    Santa Fe Jack Member

    Yes, I am aware of the advantages of DCC, and am still considering that as an option.

    In this thread, however, I'm attempting to completely vet the issues with DC. It comes down to economics, and although more complex (and complex can actually be more fun at times) DC is still a good bit cheaper, considering I have several engines that would need conversion and would want at least two controllers.

    So - the recommendations to go DCC are noted, but are not particularly useful for this thread. This thread is about working out some details of a DC system, not about the merits of DC vs DCC.

    That said, I would be interested, in the interst of fairness, to hear arguments in favor of DC over DCC besides the fact that it is cheaper. I already know the arguments in favor of DCC.
  2. MasonJar

    MasonJar It's not rocket surgery

    In that case, would it make any difference if the rotaries were wired from each power pack, versus each block? I.e. the switch is for sending power from a specific pack to any block, rather than selecting a pack to run a specific block. I am not sure that that scheme would work though, as the idea is that a powerpack run the "current" block, plus the one "ahead" of the locomotive.

    I believe that to operate properly, the "block ahead" should be empty. If it is not, then any loco running in it will come under the control of the new cab, rather than the one that is supposed to be controlling it. I don't see that there is any problem with a particular block "seeing" another powerpack momentarily given that it should be empty.

    Hope that helps.

  3. Santa Fe Jack

    Santa Fe Jack Member

    This is actually where I had started in my mind, but it was pointed out to me earlier in this thread that having the block-centric switch was how most people would do it. I hadn't even thought that way before, but in doing some thought experiments in running imagined trains around a layout drawing, I can see the advantages. Also, this requires 12 5-position switches instead of 5 12-position switches.

    I agree. In thinking through the operations, it becomes apparent that a rule of thumb ought to be that one is not allowed to switch a block between power controllers (cabs) if there is an engine on the block. That seems simple enough, and obviates the "switching through cabs" problem.

    I can see that any operator of the layout will require training on how to use it. :)
  4. pgandw

    pgandw Active Member

    From a wiring perspective - DC is pretty simple with 2 cabs or throttles. You can use SPDT or DPDT center off toggle switches to select which throttle attaches to a given block. It's even fairly reasonable to parallel the block and switch machine controls to remote areas of the layout to allow walk-around control using DC.

    But when 3 or more throttles are in use, DCC really shines. As you have discovered, even when you find the appropriate rotary block selectors, you still need a block on/off switch so you don't momentarily connect the wrong throttle when selecting with the rotary. The panel wiring gets very complex very quickly. Also, remoting to local panels further increases complexity. The DC solutions to these issues, route cab control and MZL (main, zone, local) control where written up in the '50s and early '60s in Model Railroader. If the subject interests you, I suggest those article series.

    Route cab control uses a master rotary, usually 3 or more poles and typically 20 positions or more, for each cab that you advance one stop as you go from one block to the next. The master cab rotary connects and disconnects each block in a pre-programmed (toggle and hardware logic, not software!) route set up in advance for the train.

    MZL sets up zones for local control of particular towns or switching areas, while leaving the rest of the layout controlled at the master panel.

    From an operator perspective, constantly monitoring block toggle status on a smaller layout is actually quite a bit more hassle than on a larger layout. On the smaller layout the blocks are smaller, and the trains are closer together, and must share critical blocks more often. Larger layouts with multiple operators would often put block power assignment in the dispatcher's task list.

    With DCC, because the locomotives are selectively addressed by the throttles no matter where they are, block control, toggles, rotaries, and associated wiring are no longer needed. Even though I am a confirmed DC user (still), I highly recommend DCC on any layout that regularly has more than one operator simultaneously - just for the operational convenience of not having to monitor and throw block toggles.

    The real costs of DCC for a 3 operator layout is on the order of $400+/-$50 (starter system plus 2 additional throttles) plus $30 per locomotive. There is a time cost of installing decoders, but there is a huge time cost of planning and installing the wiring of a 3 operator layout in DC.

    just my thoughts, your choices
  5. MasonJar

    MasonJar It's not rocket surgery

    The only way I can see to use the "cab-centric" rotary (great terminology, BTW), is to have each position power two blocks - i.e. position 1 powers Blocks 1 & 2, position 2 is for Blocks 2 & 3, position 3 for 3 & 4, etc. How well this might work is highly dependent on the layout of the track. It would be no problem for an oval with two powerpacks, but I can see it rapidly getting extremely complex in short order... ;)

  6. Santa Fe Jack

    Santa Fe Jack Member

    Right. I don't think cab-centric switches will work as well as block-centric ones. I intend to have block-centric rotary switches installed in a small "map" of the layout that also includes switches controlling the switch machines, and the occasional branch or end track that could be either OFF or electrically connected to the adjacent track.

    The "map", by the way, will actually take the form of a 1-900 scale park train, with track and a passenger train that does not move, but has people standing in line to board it for a ride. That sort of thing. Should be very cute.
  7. NYNH&H

    NYNH&H Member

    Engineer control is cab-centric switching. basically, each cab can turn on or off for each block. Then, an indicator light shows if someone else if using a block. This way, you can enter a block, and then turn off the one behind you for another operator. Forget about walk-around with this though. This method is for stationary cabs. In reality, DC block wiring for new layouts is dead. Either use a single power-pack, or start with a small DCC system like the Zephyr. It is $160, and you can use two of your existing power packs as throttles, and/or add walkaround DCC throttles. DCC decders are $13/loco if you buy 10 decoders from NCE, about $16/loco otherwise, NCE or Digitrax. I personally prefer Digitrax, as they are shrink-wrapped, so they don't short on exposed wiring or electified parts. You only need to convert two locos in the beginning, and do more as time/money permits. DCC is the way to go. As for those annoying block toggles, you can havea cutoff switch, that works just fine. In Easy Model Railroad Wiring, there is some way to use a pushbutton, must be a usually ON, not a usually OFF. Don't worry about that though, go DCC.
  8. 60103

    60103 Pooh Bah

    Jack: the disadvantage of the rotary is as you indicated. And the only solution I see is the "clutch" pushbutton.
    The other method is called route cab control and it was described in Model Railroader about 1958. I didn't understand it then, and I think I know what they were doing now, but I wouldn't want to try it. What I think happens is that your rotary on the cab follows the train along, block by block, and the wiring somehow follows it through the way turnouts are set.
    If you want to try it, find someone who is dismantling an early dial telephone exchange, and salvage the relays.

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